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Xiaomi Redmi K40 Display Technology Shoot-Out

 

Dr. Raymond M. Soneira

President, DisplayMate Technologies Corporation

 

Copyright © 1990-2021 by DisplayMate Technologies Corporation. All Rights Reserved.

This article, or any part thereof, may not be copied, reproduced, mirrored, distributed or incorporated

into any other work without the prior written permission of DisplayMate Technologies Corporation

 

 

 

Redmi K40

 

POCO F3

 

Introduction and Overview

The key element for a great Smartphone has always been a truly innovative and top performing display, and the best leading edge Smartphones have always flaunted their super high tech displays. It is the display performance that determines how good and how beautiful everything on the Smartphone looks, including the camera photos, videos, movies, web content, plus all of your Apps, and also how readable and how usable the screen is in High Ambient Lighting. The Display is the Crown Jewel of the Smartphone!

 

In this Display Technology Shoot-Out article series we Only Test and Only Cover the Very Best State-of-the-Art Top Performing Top Tier Smartphone Displays. The articles are designed to promote Superior Display Performance so that reviewers, analysts, journalists, and consumers all Recognize and Appreciate Display Excellence, and also to reward and encourage manufacturers to produce top performing displays for their products.

 

In this article we lab test, measure, analyze, and evaluate in depth the display on the Redmi K40 and POCO F3.

The Redmi K40 and POCO F3 are the same Smartphone with the same display. The different names are for different sales regions.

Whenever we refer to the Redmi K40, the identical Results, Conclusions, and Ratings also apply to the POCO F3.

 

This is an independent scientific objective lab test and analysis of OLED displays written for reviewers, analysts, journalists, and consumers. It is the latest edition in our ten year article series that has lab tested, tracked and analyzed the development of mobile OLED displays and display technology, from its early beginnings in 2010, when OLED displays started out in last place, into a rapidly improving and evolving display technology that now has a commanding first place lead and continues pushing ahead aggressively.

 

All of the DisplayMate Display Performance Grades, Ratings and Awards are based entirely on the extensive objective Lab tests and measurements that we also publish, so that everyone can judge and compare the display performance data for themselves as well. As Display Performance continues to improve each year we have and will continue to raise the Performance Levels necessary to receive a DisplayMate Best Smartphone Display Award and A+ Display Rating. As a result, only the Very Best Displays will continue to receive A+ Ratings each year.

 

Xiaomi Redmi K40 Conclusion Summary

Below is a Summary of the Conclusion

See the Conclusion section for the details.

 

All of the DisplayMate Display Performance Grades, Ratings and Awards are based entirely on the extensive objective Lab tests and measurements that we also publish, so that everyone can judge and compare the display performance data for themselves as well.

 

Based on our extensive Lab Tests and Measurements the Redmi K40 delivers Uniformly Consistent Top Tier Display Performance and receives All Green [Very Good to Excellent] Ratings in All DisplayMate Lab Test Display Performance and Accuracy Categories. As a Result, the Redmi K40 has earned DisplayMate’s Highest Overall Display Assessment Rating and Highest Display Performance Grade of A+.

 

The Redmi K40 has a Very Impressive Excellent Top Tier World Class Smartphone Display with close to Text Book Perfect Calibration Accuracy and Performance that is Visually Indistinguishable From Perfect. Based on our objective Lab Tests and Measurements the Redmi K40 receives a DisplayMate Best Smartphone Display Award earning DisplayMate’s highest ever Display Performance Grade of A+ and setting or matching 11 Smartphone Display Performance Records including 5 that are Visually Indistinguishable From Perfect.

 

All of these Results, Conclusions, and Ratings also apply to the POCO F3. As a result, the Redmi K40 and POCO F3 join the very select Top Tier of the Best Smartphone Displays. This demonstrates that Xiaomi recognizes the importance of Display Excellence and has made a major commitment to improving Smartphone Display Performance.

 

Display Shoot-Out Lab Measurements Comparison Table

Below we examine in-depth the OLED display performance of the Xiaomi Redmi K40 based on objective Lab Measurement data

and criteria in the following sections:  Display SpecificationsOverall AssessmentsScreen Reflections,

Brightness and ContrastColors and IntensitiesAbsolute Color Accuracy,  Viewing AnglesOLED Spectra

 

For comparisons with the other leading Smartphone displays see our Mobile Display Technology Shoot-Out article series.

 

Categories

 Xiaomi Redmi K40

Comments

Display Technology

 

OLED Display with Diamond Pixels

6.65 inch Diagonal  /  16.9 cm Diagonal

Excluding the Rounded Corners

 

Organic Light Emitting Diode

Diamond Pixels with Diagonal Sub-Pixel Symmetry.

 

Screen Aspect Ratio

 

20 : 9 = 2.22

Higher Aspect Ratio

Most Smartphones and Widescreen TVs have 16 : 9 = 1.78

 

Height to Width Aspect Ratio

The Redmi K40 display screen is 25% longer than

most Smartphones and widescreen 16:9 TV content.

Screen Size

 

     2.73  x   6.07 inches

6.94  x 15.43 cm

 

Display Width and Height in inches and cm.

 Screen Area

 

16.6 square inches  /  107 square cm

After Subtracting the Camera Opening but not the Rounded Corners

 

A better measure of size than the Diagonal.

Front Camera Opening Size

Front Camera Opening has less than 0.1 percent of the Screen Area

Diameter is 0.13 inches  /  3.2 mm

Front Camera Opening is by the Top Left

of the Screen.

Supported Color Gamuts

 

                          Auto mode  –  Wide Color Gamut with Higher Contrast

           Original DCI-P3 mode  –  DCI-P3 Standard Color Gamut

            Original sRGB mode  –  sRGB / Rec.709 Standard Color Gamut

Saturated mode  –  Native OLED Color Gamut with Higher Contrast

Automatic Color Management for Content with ICC Color Profiles

 

The Redmi K40 supports 2 Standard Color Gamuts: sRGB and the new wider DCI-P3 Color Gamut that is used in 4K Ultra HD TV content.

 

 

Display Refresh Rates

Display Refresh Frames Per Second FPS

Normal FPS:  60 Hz Refresh

High  FPS:  120 Hz Refresh for Smoother Scrolling and Motion

 

Higher Refresh Rates improve image Scrolling

plus Video and Motion Performance in Apps,

and may reduce Screen Flicker that some

people experience.

 

Display Resolution

 

2400 x 1080 pixels

2K+   FHD+

 

Screen Pixel Resolution.

Standard Full HD is 1920x1080

Total Number of Pixels

 

2.6 Mega Pixels

 

Total Number of Display Pixels.

Pixels Per Inch  PPI

395 PPI with Diamond Pixels

Excellent

 

Sharpness depends on the viewing distance and PPI.

See this on the visual acuity for a true Retina Display

 

Sub-Pixels Per Inch  SPPI

   

    Red  279 SPPI

 Green  395 SPPI

   Blue  279 SPPI

 

Diamond Pixel displays have only half the number of

Red and Blue Sub-Pixels as RGB Stripe displays.

At High PPI this is generally not visible due to

the use of Sub-Pixel Rendering.

Total Number of Sub-Pixels

   Red  1.3 Million Sub-Pixels

Green  2.6 Million Sub-Pixels

  Blue  1.3 Million Sub-Pixels

Diamond Pixel displays have only half the number of

Red and Blue Sub-Pixels as RGB Stripe displays.

At High PPI this is generally not visible due to

the use of Sub-Pixel Rendering.

20/20 Vision Distance

where Pixels or Sub-Pixels

are Not Resolved

           8.7 inches / 22.1 cm  for White and Green Sub-Pixels with 20/20 Vision

   12.3 inches / 31.3 cm  for Red and Blue Sub-Pixels with 20/20 Vision

For 20/20 Vision the minimum Viewing Distance

where the screen appears perfectly sharp to the eye.

At 10 inches from the screen 20/20 Vision is 344 PPI.

Display Sharpness

at Typical Viewing Distances

Redmi K40 Display appears Perfectly Sharp

Pixels are not Resolved with 20/20 Vision

at Typical Viewing Distances of

     12 to 18 inches

30 to 46 cm

 

The Typical Viewing Distances for this screen size

are in the range of 12 to 18 inches or 25 to 46 cm.

 

Also note that eye’s resolution is much lower for

Red and Blue color content than White and Green.

 

 

Appears Perfectly Sharp

at Typical Viewing Distances

 

 Yes

Typical Viewing Distances are 12 to 18 inches

or 30 to 46 cm for this screen size.

 

Overall Display Performance Assessments

This section summarizes the results for all of the extensive Lab Measurements and Viewing Tests performed on the display.

See  Screen ReflectionsBrightness and ContrastColors and IntensitiesAbsolute Color AccuracyViewing AnglesOLED Spectra

 

The Redmi K40 has Automatic Color Management that switches to the appropriate Color Gamut for Content with ICC Color Profiles.

 

Here we provide results for the Auto Color mode, which has a Wide Color Gamut and Higher Image Contrast,

the Original DCI-P3 mode, which is calibrated for the new DCI-P3 Gamut that is used in 4K Ultra HD TVs,

and the Original sRGB mode, which is calibrated for the sRGB / Rec.709 Gamut that is used for most current

consumer photo, video, web, and computer content.

 

Categories

Auto Color mode

Wide Color Gamut

Original Color mode

DCI-P3 Content

Original Color mode

sRGB Content

Comments

Viewing Tests

in Subdued Ambient Lighting

 

 

 

 

Very Good Images

Photos and Videos

have Vivid Color

and Higher Contrast

 

Intentionally Vivid Colors

Excellent Images

Photos and Videos

have Excellent Color

and Accurate Contrast

 

Accurate DCI-P3 Content

Excellent Images

Photos and Videos

have Excellent Color

and Accurate Contrast

 

Accurate sRGB Content

The Viewing Tests examine the accuracy of

photographic images by comparing the displays

to a calibrated studio monitor and TV.

 

 

 

 

Variation with Viewing Angle

Colors and Brightness

 

See Viewing Angles

 

Color Shifts

Small to Medium

with Viewing Angle

 

Small Brightness Shifts

with Viewing Angle

Color Shifts

Small to Medium

with Viewing Angle

 

Small Brightness Shifts

with Viewing Angle

Color Shifts

Small to Medium

with Viewing Angle

 

Small Brightness Shifts

with Viewing Angle

The Redmi K40 display has a relatively small

decrease in Brightness with Viewing Angle and

relatively small Color Shifts with Viewing Angle.

 

See the Viewing Angles section for details.

 

 

Overall Display Assessment

Lab Tests and Measurements

Excellent OLED Display

Vivid Color Mode

Excellent OLED Display

Accurate DCI-P3 Content

Excellent OLED Display

Accurate sRGB Content

The Redmi K40 OLED Display performed

very well in the Lab Tests and Measurements.

 

 

Absolute Color Accuracy

Measured over Entire Gamut

 

See Figure 2 and Colors

 Good Color Accuracy

Colors More Saturated

Intentionally Vivid Colors

 

Excellent Color Accuracy

Color Errors are Very Small

Accurate DCI-P3 Content

 

Excellent Color Accuracy

Color Errors are Very Small

Accurate sRGB Content

 

Absolute Color Accuracy is measured with a

Spectroradiometer for 41 Reference Colors

uniformly distributed within the entire Color Gamut.

 

See Figure 2 and Colors for details.

Image Contrast Accuracy

 

See Figure 3 and Contrast

Very Good Accuracy

Image Contrast

Intentionally Higher

Excellent Accuracy

Image Contrast

Very Accurate

Excellent Accuracy

Image Contrast

Very Accurate

The Image Contrast Accuracy is determined by

measuring the Log Intensity Scale and Gamma.

 

See Figure 3 and Contrast for details.

Performance in Ambient Light

Display Brightness

Screen Reflectance

Contrast Rating

 

See Brightness and Contrast

See Screen Reflections

High Display Brightness

Very Low Reflectance

 

High Contrast Rating

for Ambient Light

 

Higher Brightness with

Auto Brightness On

High Display Brightness

Very Low Reflectance

 

High Contrast Rating

for Ambient Light

 

Higher Brightness with

Auto Brightness On

High Display Brightness

Very Low Reflectance

 

High Contrast Rating

for Ambient Light

 

Higher Brightness with

Auto Brightness On

Smartphones are seldom used in the dark.

 

Screen Brightness and Reflectance determine

the Contrast Rating for High Ambient Light.

 

See the Brightness and Contrast section for details.

See the Screen Reflections section for details.

 

 

Overall Display Calibration

Image and Picture Quality

Lab Tests and Viewing Tests

Vivid Color Mode

Intentionally Vivid Colors

and Higher Image Contrast

Excellent Calibration

Accurate DCI-P3 Content 

 

Excellent Calibration

Accurate sRGB Content

 

The Redmi K40 has sRGB and DCI-P3 modes

that deliver accurately calibrated colors and images

and a Vivid Color mode that is preferred by

some users and for some applications.

 

Overall Display Grade

Overall Assessment

 

Overall Xiaomi Redmi K40 Display Grade is Excellent A+

DisplayMate Best Smartphone Display Award

with 11 Smartphone Display Performance Records

including 5 that are Visually Indistinguishable From Perfect

An Excellent Top Tier World Class Smartphone Display

 

The Redmi K40 display delivers Excellent

Image Quality, has both Original sRGB and

Original DCI-P3 modes and an Auto Color mode with

a Wide Color Gamut, has High Screen Brightness

and low Reflectance, has good Viewing Angles, and

is an all around Top Performing Smartphone Display.

 

Vivid Color Mode

Also Best for Viewing in

High Ambient Light

Accurate DCI-P3 Content

For Viewing 4K UHD TV

DCI-P3 Cinema Content

Accurate sRGB mode

For Viewing Most Content

Photo Video Movie Web

Categories

Auto Color mode

Wide Color Gamut

Original Color mode

DCI-P3 Content

Original Color mode

sRGB Content

Comments

 

Xiaomi Redmi K40 Conclusions:   A Record Setting Impressive Smartphone Display…

The primary goal of this Display Technology Shoot-Out article series has always been to publicize and promote display excellence so that consumers, journalists, reviewers, and even manufacturers are aware of and appreciate the very best in displays and display technology. We point out which manufacturers and display technologies are leading and advancing the state-of-the-art for displays by performing comprehensive and objective scientific Lab Tests and Measurements together with in-depth analysis. We point out who is leading, who is behind, who is improving, and sometimes (unfortunately) who is back pedaling.

 

All of the DisplayMate Display Performance Grades, Ratings and Awards are based entirely on the extensive objective Lab tests and measurements that we also publish, so that everyone can judge and compare the display performance data for themselves as well.

 

With consumers now spending rapidly increasing amounts of time watching content on their Smartphones, the shift in emphasis from primarily improving Display Hardware Performance to enhancing the overall Display Picture Quality and Color Accuracy is an important step that DisplayMate Technologies has been pushing for many years in our Display Technology Shoot-Out article series, so it is great to see manufactures improving and then competing on these DisplayMate Lab Measurement Objective Display Performance Metrics.

 

· All of these Results, Conclusions, and Ratings also apply to the POCO F3.

 

The Xiaomi Redmi K40 sets or matches 11 Smartphone Display Performance Records for:

Numerical Display Performance Differences that are Visually Indistinguishable are considered Matched and Tied Performance Records.

 

· Highest   Absolute Color Accuracy  (0.6 JNCD)  –  Visually Indistinguishable From Perfect.

 

· Highest   Image Contrast Accuracy and Intensity Scale Accuracy  (2.24 Gamma)  –  Visually Indistinguishable From Perfect.

 

· Smallest  Shift in Color Accuracy and Intensity Scale with the Image Content APL  (0.2 JNCD)  –  Visually Indistinguishable From Perfect.

 

· Smallest  Shift in Image Contrast and Intensity Scale with the Image Content APL  (0.02 Gamma)  –  Visually Indistinguishable From Perfect.

 

· Smallest  Change in Peak Luminance with the Image Content Average Picture Level APL  (2 percent)  –  Visually Indistinguishable From Perfect.

 

· Highest   Full Screen Brightness for OLED Smartphones  (905 nits at 100% APL).

 

· Highest   Peak Display Brightness  (1,340 nits for Low APL).

 

· Largest   Native Color Gamut  (113% DCI-P3 and 142% sRGB / Rec.709 for the Saturated Color Mode).

 

· Highest   Contrast Ratio  (Infinite).

 

· Lowest    Screen Reflectance  (4.6 percent).

 

· Highest   Contrast Rating in Ambient Light  (197 for 100% APL and 291 for Peak Brightness).

.

The Xiaomi Redmi K40 earns our Highest A+ Display Performance Assessment Rating

OLED has evolved into a highly refined and mature display technology that now produces the best and highest performance displays for Smartphones.

OLED Display Performance continues to provide major Record Setting improvements with every new generation.

 

Xiaomi has concentrated on significantly raising the on-screen Absolute Picture Quality and Absolute Color Accuracy of the OLED display by implementing Precision Factory Display Calibration, moving the overall Redmi K40 Display Performance up to Record Setting Outstanding Levels with close to Text Book Perfect Calibration Accuracy that is Visually Indistinguishable From Perfect.

 

DisplayMate Display Performance Ratings:

All of the Results in this article are based Entirely on our Objective and Extensive DisplayMate Lab Tests and Measurements that are all listed in the sections below.

 

· To get a DisplayMate A Display Performance Rating the display must get All Green [Very Good to Excellent] Ratings for All of the Display Tests and Measurements [except for Color Shifts at 30 degrees Viewing Angle, which are deemed less important].

 

· Then to get a DisplayMate A+ Display Performance Rating the Average Absolute Color Accuracy and the Average Absolute Color Accuracy Shifts with Average Picture Level APL must All be less than 1.0 JNCD, and the Largest Color Errors must All be less than 3.0 JNCD.

 

The Redmi K40 delivers Uniformly Consistent Top Tier Display Performance and receives All Green [Very Good to Excellent] Ratings in All DisplayMate Lab Test Display Performance and Accuracy Categories and has Absolute Color Accuracy much better than 1.0 JNCD.

 

The Redmi K40 display meets all of the criteria and requirements for a DisplayMate A+ Grade, earning DisplayMate’s Highest Overall Display Assessment Rating and Highest Display Performance Grade of A+.

 

· All of these Results, Conclusions, and Ratings also apply to the POCO F3.

 

DisplayMate Display Performance Rating and Best Smartphone Display Award

Based on our extensive Lab Tests and Measurements the Redmi K40 has a Very Impressive Excellent Top Tier World Class Smartphone Display with close to Text Book Perfect Calibration Accuracy and Performance that is Visually Indistinguishable From Perfect. Based on our objective Lab Tests and Measurements the Redmi K40 receives a DisplayMate Best Smartphone Display Award earning DisplayMate’s highest ever Display Performance Grade of A+ and setting or matching 11 Smartphone Display Performance Records including 5 that are Visually Indistinguishable From Perfect that are listed above.

 

· All of these Results, Conclusions, and Ratings also apply to the POCO F3.

 

The Redmi K40 and POCO F3 join the very select Top Tier of Smartphone Displays which all provide Close to Text Book Perfect Calibration Accuracy and Performance that is Visually Indistinguishable From Perfect, so they all received and maintain Concurrent DisplayMate Best Smartphone Display Awards. All are Excellent State-of-the-Art Displays, each is better in some Display Performance Categories, but None are Best in All the Display Performance Categories. Note that measured numerical display performance differences that are Visually Indistinguishable are equivalent.

 

As Display Performance continues to improve we have and will continue to raise the Performance Levels necessary to receive a DisplayMate Best Smartphone Display Award and an A+ Display Rating, so The Top Tier of Smartphone Displays will continue to evolve and change with each new display generation, but only the Very Best Displays will continue to receive A+ Ratings each year.

 

 

Screen Reflections

All display screens are mirrors good enough to use for personal grooming – but that is actually a very bad feature…

We measured the light reflected from all directions and also direct mirror (specular) reflections, which are much more

distracting and cause more eye strain. Many Smartphones still have greater than 10 percent reflections that make

the screen much harder to read even in moderate ambient light levels, requiring ever higher brightness settings that

waste precious battery power. Manufacturers should reduce the mirror reflections with anti-reflection coatings and

matte or haze surface finishes.

 

Our Lab Measurements include Average Reflectance for Ambient Light from All Directions and for Mirror Reflections.

We use an Integrating Hemisphere and a highly collimated pencil light beam together with a Spectroradiometer.

Note that the Screen Reflectance is exactly the same for all of the Redmi K40 Color Modes.

 

The Redmi K40 has close to the lowest Screen Reflectance level that we have ever measured for a Smartphone.

These results are extremely important for screen readability, picture quality, and color accuracy in ambient light.

 

Categories

 Redmi K40

Comments

Average Screen Reflection

Light From All Directions

4.6 percent

for Ambient Light Reflections

Excellent

Measured using an Integrating Hemisphere and

a Spectroradiometer.

The lowest value we have ever measured

for a Smartphone is 4.3 percent.

Mirror Reflections

Percentage of Light Reflected

 5.6 percent

for Mirror Reflections

Very Good

These are the most annoying types of Reflections.

Measured using a Spectroradiometer and a narrow

collimated pencil beam of light reflected off the screen.

The lowest value we have ever measured

for a Smartphone is 5.3 percent.

 

Brightness and Contrast

The Contrast Ratio is the specification that gets the most attention, but it only applies for low ambient light, which is seldom

the case for mobile displays.

 

Much more important is the Contrast Rating for High Ambient Light, which indicates how easy it is to read the screen under

high ambient lighting and depends on both the Maximum Brightness and the Screen Reflectance. The larger the better.

The display’s actual on-screen Contrast Ratio changes with the Ambient Light lux level and is proportional to the Contrast Rating.

 

Categories

Auto Color mode

Wide Color Gamut

Original Color mode

DCI-P3 Content

Original Color mode

sRGB Content

Comments

Home Screen Peak Brightness

Measured for White

Brightness 566 cd/m2

Excellent

Brightness 461 cd/m2

Very Good

Brightness 461 cd/m2

Very Good

The Peak Brightness for White on the Home Screen.

 

Measured Average Brightness

50% Average Picture Level

Brightness 551 cd/m2

Excellent

Brightness 466 cd/m2

Very Good

Brightness 466 cd/m2

Very Good

This is the Brightness for typical screen content

that has a 50% Average Picture Level.

Measured Full Brightness

100% Full Screen White

Brightness 497 cd/m2

Very Good

Brightness 470 cd/m2

Very Good

Brightness 471 cd/m2

Very Good

This is the Brightness for a screen that is entirely

all white with 100% Average Picture Level.

Measured Peak Brightness

1% Average Picture Level

Brightness 640 cd/m2

Excellent

Brightness 463 cd/m2

Very Good

Brightness 463 cd/m2

Very Good

This is the Peak Brightness for a screen that

has only a tiny 1% Average Picture Level.

Dynamic Brightness

Change in Luminance with

Average Picture Level APL

22 percent Decrease

Intentionally Large

2 percent Decrease

Excellent

2 percent Decrease

Excellent

This is the percent Brightness decrease with APL

Average Picture Level. Ideally should be 0 percent.

 

Low Ambient Light

Lowest Peak Brightness

Super Dimming Mode

Brightness Slider to Minimum

2 cd/m2

For Very Low Light

2 cd/m2

For Very Low Light

2 cd/m2

For Very Low Light

This is the Lowest Brightness with the Slider set to

Minimum. This is useful for working in very dark

environments. Picture Quality remains Excellent.

Black Brightness at 0 lux

at Maximum Brightness Setting

0 cd/m2

Outstanding

0 cd/m2

Outstanding

0 cd/m2

Outstanding

Black Brightness is important for Low Ambient Light,

which is seldom the case for mobile devices.

Contrast Ratio at 0 lux

Relevant for Low Ambient Light

Infinite

Outstanding

Infinite

Outstanding

Infinite

Outstanding

Only relevant for Low Ambient Light,

which is seldom the case for mobile devices.

Always-On Display Mode

White Luminance

Low    5 cd/m2

High 48 cd/m2

Low    5 cd/m2

High  46 cd/m2

Low    5 cd/m2

High  46 cd/m2

 

Displayed image content when the Smartphone

is in Standby Mode.

 

 

High Brightness Mode

Automatic Brightness in High Ambient Light

Measured High Brightness Mode

50% Average Picture Level

 

High Brightness Mode

1,051 cd/m2

Excellent

High Brightness Mode

1,008 cd/m2

Excellent

High Brightness Mode

1,008 cd/m2

Excellent

This is the Brightness for typical screen content

that has a 50% Average Picture Level.

 

Measured High Brightness Mode

100% Full screen White

 

High Brightness Mode

905 cd/m2

Excellent

High Brightness Mode

880 cd/m2

Excellent

High Brightness Mode

880 cd/m2

Excellent

This is the Brightness for a screen that is entirely

all white with 100% Average Picture Level.

 

Measured High Brightness Mode

1% Average Picture Level

 

High Brightness Mode

1,340 cd/m2

Excellent

High Brightness Mode

1,253 cd/m2

Excellent

High Brightness Mode

1,253 cd/m2

Excellent

This is the Peak Brightness for a screen that

has only a small 1% Average Picture Level.

 

 

High Ambient Light Contrast Rating

Contrast Rating

for High Ambient Light

 

The Higher the Better

for Screen Readability

in High Ambient Light

108 – 139

With Manual Brightness

Very Good

 

197 – 291

High Brightness Mode

Excellent

101 – 102

With Manual Brightness

Very Good

 

191 – 272

High Brightness Mode

Excellent

101 – 102

With Manual Brightness

Very Good

 

191 – 272

High Brightness Mode

Excellent

 

Depends on the Screen Reflectance and Brightness.

Defined as Maximum Brightness / Average Reflectance.

 

The display’s actual on-screen Contrast Ratio

changes with the Ambient Light lux level and

is proportional to the Contrast Rating.

Screen Readability

in High Ambient Light

Very Good  A

With Manual Brightness

 

Excellent  A+

With Auto Brightness On

Very Good  A

With Manual Brightness

 

Excellent  A+

With Auto Brightness On

Very Good  A

With Manual Brightness

 

Excellent  A+

With Auto Brightness On

 

Indicates how easy it is to read the screen

under High Ambient Lighting. Depends on

both the Screen Reflectance and Brightness.

See High Ambient Light Screen Shots

 

Colors and Intensities

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1

Color Gamuts

Click to Enlarge

 

Figure 2

Color Accuracy

Click to Enlarge

 

Figure 3

Intensity Scales

Click to Enlarge

 

Figure 4

Color Shifts

Click to Enlarge

 

 

The Color Gamut, Intensity Scale, and White Point determine the quality and accuracy of all displayed images and all

the image colors. Bigger is definitely Not Better because the display needs to match all the Standards that were used

when the content was produced.

 

The Redmi K40 has Automatic Color Management that switches to the appropriate Color Gamut for Content with ICC Color Profiles.

 

The Redmi K40 also has a Saturated Color mode with the Native Color Gamut of the OLED Display,

which is 113% of the DCI-P3 Gamut and 142% of the sRGB Gamut.

 

Categories

Auto Color mode

Wide Color Gamut

Original Color mode

DCI-P3 Content

Original Color mode

sRGB Content

Comments

Color of White

Color Temperature in degrees

Measured in the dark at 0 lux

 

The White Point is Adjustable

with the Reading Mode

Adaptive Colors Mode

Interactive Touch Screen

 

7,530 K

2.6 JNCD from D65 White

 

 

Intentionally Bluish Mode

 

 

See Figure 1

6,440 K

0.5 JNCD from D65 White

Very Close to Standard

 

Excellent

Accurate White Point

 

See Figure 1

6,450 K

0.5 JNCD from D65 White

Very Close to Standard

 

Excellent

Accurate White Point

 

See Figure 1

D65 with 6,500 K is the standard color of White

for most Consumer Content and needed for

accurate color reproduction of all images.

 

JNCD is a Just Noticeable Color Difference.

White Point accuracy is more critical than other colors.

 

See Figure 1 for the plotted White Points.

See Figure 2 for the definition of JNCD.

 

Color Gamut

Measured in the dark at 0 lux

 

See Figure 1

103 percent

DCI-P3 Cinema Gamut

Intentionally Vivid Colors

130 percent

sRGB / Rec.709 Gamut

Intentionally Vivid Colors

 

See Figure 1

 

101 percent

DCI-P3 Cinema Gamut

Very Close to Standard

 

Excellent

Accurate DCI-P3 Content

 

See Figure 1

104 percent

sRGB / Rec.709 Gamut

Very Close to Standard

 

Excellent

Accurate sRGB Content

 

See Figure 1

Most current consumer content uses sRGB / Rec.709.

The new 4K UHD TVs and Digital Cinema use DCI-P3.

 

A Wide Color Gamut is useful in High Ambient Light

and for some applications. It can be used with Color

Management to dynamically change the Gamut.

 

See Figure 1

 

Absolute Color Accuracy

Absolute Color Accuracy

Average Color Error at 0 lux

 

For 41 Reference Colors

Just Noticeable Color Difference

 

See Figure 2

Average Color Error

From sRGB / Rec.709

Δ(u’v’) = 0.0269

6.7 JNCD

 

Intentionally Vivid Colors

Vivid Color Mode

 

See Figure 2

Average Color Error

From DCI-P3

Δ(u’v’) = 0.0023

0.6 JNCD

 

Excellent Accuracy

Accurate DCI-P3 Content

 

See Figure 2

 Average Color Error

From sRGB / Rec.709

Δ(u’v’) = 0.0025

 0.6 JNCD

 

Excellent Accuracy

Accurate sRGB Content

 

See Figure 2

 

JNCD is a Just Noticeable Color Difference.

 

See Figure 2 for the definition of JNCD and for the

Accuracy Plots showing the measured Color Errors.

 

Color Errors below 2.0 JNCD are Excellent.

Color Errors below 3.5 JNCD are Very Good.

Color Errors 3.5 to 7.0 JNCD are Good.

Color Errors above 7.0 JNCD are Poor.

Absolute Color Accuracy

Largest Color Error at 0 lux

 

For 41 Reference Colors

Just Noticeable Color Difference

 

See Figure 2

Largest Color Error

From sRGB / Rec.709

Δ(u’v’) = 0.0788

19.7 JNCD

for 50% Blue

 

Intentionally Vivid Colors

Vivid Color Mode

 

See Figure 2

Largest Color Error

From DCI-P3

Δ(u’v’) = 0.0048

1.2 JNCD

for 75% Blue

 

Excellent Accuracy

Accurate DCI-P3 Content

 

See Figure 2

Largest Color Error

From sRGB / Rec.709

Δ(u’v’) = 0.0088

2.2 JNCD

for 100% Red

 

Very Good Accuracy

Accurate sRGB Content

 

See Figure 2

 

JNCD is a Just Noticeable Color Difference.

 

See Figure 2 for the definition of JNCD and for the

Accuracy Plots showing the measured Color Errors.

 

Color Errors below 2.0 JNCD are Excellent.

Color Errors below 3.5 JNCD are Very Good.

Color Errors 3.5 to 7.0 JNCD are Good.

Color Errors above 7.0 JNCD are Poor.

 

Changes in Absolute Color Accuracy with Average Picture Level APL

Measured Shifts in the Absolute Color Accuracy with Image Content from Low 1% APL to High 50% APL

Shift in the Color of White

 

Just Noticeable Color Difference

 

See Figure 4

White Point Color Shift

from Low to High APL

Δ(u’v’) = 0.0026

0.7 JNCD

 

Excellent

 

White Point Color Shift

from Low to High APL

Δ(u’v’) = 0.0011

0.3 JNCD

 

Excellent

 

See Figure 4

White Point Color Shift

from Low to High APL

Δ(u’v’) = 0.0017

0.4 JNCD

 

Excellent

 

See Figure 4

 

JNCD is a Just Noticeable Color Difference

 

See Figure 2 for the definition of JNCD.

See Figure 4 for the measured Color Shifts.

 

Color Shifts below 2.0 JNCD are Excellent

Color Shifts below 3.5 JNCD are Very Good.

Color Shifts 3.5 to 7.0 JNCD are Good.

Color Shifts above 7.0 JNCD are Poor.

Average Color Shift

 

For 41 Reference Colors

Just Noticeable Color Difference

 

See Figure 4

Auto Color mode

 

Intentionally Variable

 

 

 

Average Color Shift

from Low to High APL

Δ(u’v’) = 0.0008

0.2 JNCD

 

Excellent

 

See Figure 4

Average Color Shift

from Low to High APL

Δ(u’v’) = 0.0010

0.2 JNCD

 

Excellent

 

See Figure 4

 

JNCD is a Just Noticeable Color Difference.

 

See Figure 2 for the definition of JNCD.

See Figure 4 for the measured Color Shifts.

 

Color Shifts below 2.0 JNCD are Excellent

Color Shifts below 3.5 JNCD are Very Good.

Color Shifts 3.5 to 7.0 JNCD are Good.

Color Shifts above 7.0 JNCD are Poor.

Largest Color Shift

 

For 41 Reference Colors

Just Noticeable Color Difference

 

See Figure 4

Auto Color mode

 

Intentionally Variable

 

 

 

Largest Color Shift

from Low to High APL

Δ(u’v’) = 0.0014

0.3 JNCD

for 75% Red

 

Excellent

 

See Figure 4

Largest Color Shift

from Low to High APL

Δ(u’v’) = 0.0019

0.5 JNCD

for 100% Cyan-Blue

 

Excellent

 

See Figure 4

 

JNCD is a Just Noticeable Color Difference

 

See Figure 2 for the definition of JNCD.

See Figure 4 for the measured Color Shifts.

 

Color Shifts below 2.0 JNCD are Excellent

Color Shifts below 3.5 JNCD are Very Good.

Color Shifts 3.5 to 7.0 JNCD are Good.

Color Shifts above 7.0 JNCD are Poor.

 

Intensity Scale and Image Contrast Accuracy

Dynamic Brightness

Change in Luminance with

Average Picture Level APL

22 percent Decrease

Intentionally Large

2 percent Decrease

Excellent

2 percent Decrease

Excellent

This is the percent Brightness decrease with APL

Average Picture Level. Ideally should be 0 percent.

Intensity Scale and

Image Contrast

 

See Figure 3

Smooth and Straight

Very Good

Slightly Too Steep

 

Intentionally Steeper

Very Smooth and Straight

Excellent

Very Accurate

 

See Figure 3

Very Smooth and Straight

Excellent

Very Accurate

 

See Figure 3

 

The Intensity Scale controls image contrast needed

for accurate Image Contrast and Color reproduction.

See Figure 3

Gamma for the Intensity Scale

Larger has more Image Contrast

 

See Figure 3

Gamma 2.45

Very Good

Gamma Intentionally High

Gamma 2.24

Excellent

Gamma Very Accurate

 Gamma 2.24

Excellent

Gamma Very Accurate

Gamma is the log slope of the Intensity Scale.

Gamma of 2.20 is the standard and needed for

accurate Image Contrast and Color reproduction.

See Figure 3

 

Image Contrast Accuracy

Very Good

Excellent

Excellent

See Figure 3

 

 

Viewing Angles

The variation of Brightness, Contrast, and Color with Viewing Angle is especially important for Smartphones because

of their larger screen and multiple viewers. The typical manufacturer 176+ degree specification for LCD Viewing Angle

is nonsense because that is where the Contrast Ratio falls to a miniscule 10. For most LCDs there are substantial

degradations at less than ±30 degrees, which is not an atypical Viewing Angle for Smartphones and Tablets.

 

The Viewing Angle variations are essentially identical for all of the Redmi K40 Color Modes.

 

Note that the Viewing Angle performance is also very important for a single viewer because the Viewing Angle can vary

significantly based on how the Smartphone is held. The Viewing Angle can be very large if resting on a table or desk.

 

· The Redmi K40 display has a Brightness (Luminance) fall off with Viewing Angle that is much smaller than the best LCD displays.

 

Color Shifts:

The variation of Brightness, Contrast, and Color with Viewing Angle is especially important for Smartphones because

of their larger screen and multiple viewers. The typical manufacturer 176+ degree specification for LCD Viewing Angle

is nonsense because that is where the Contrast Ratio falls to a miniscule 10. For most LCDs there are substantial

degradations at less than ±30 degrees, which is not an atypical Viewing Angle for Smartphones and Tablets.

 

· The White Point Color Shift is the most viewer noticeable Color Shift with Viewing Angle because it is often the screen background.

The Redmi K40 has a small White Shift of just 1.6 JNCD at 30 degrees, which is unlikely to be noticeable.

 

· The Color Shifts throughout the entire Color Gamut vary as combinations of the Primary Color Shifts.

· The Color Shifts for the Red and Green Primaries are both relatively small, with 2.0 JNCD for Green and 2.7 JNCD for Red at 30 degrees.

· The Color Shift for the Blue Primary at 30 degrees Viewing Angle is 5.7 JNCD, much greater than the 3.5 JNCD limit for a

Green Very Good Rating. But Color Shifts in the Blue Region are less visually noticeable as discussed in this article

 

Almost all current model OLED Smartphone Displays have either 1 or 2 Primary Color Shift Yellow ratings.

 

Categories

Auto Color mode

Wide Color Gamut

Original Color mode

DCI-P3 Content

Original Color mode

sRGB Content

Comments

Brightness Decrease

at a 30 degree Viewing Angle

29 percent Decrease

Small Decrease

Very Good

Most screens become less bright when tilted.

LCD decrease is generally greater than 50 percent.

Contrast Ratio at 0 lux

at a 30 degree Viewing Angle

Infinite Contrast Ratio

Outstanding

A measure of screen readability when the screen

is tilted under low ambient lighting.

 

White Point Color Shift

at a 30 degree Viewing Angle

Small Color Shift

Δ(u’v’) = 0.0064

 1.6 JNCD  Excellent

JNCD is a Just Noticeable Color Difference.

See Figure 2 for the definition of JNCD.

Color Shifts below 2.0 JNCD are Excellent

 

Color Shifts for the Primaries

Red Primary Color Shift

at a 30 degree Viewing Angle

Small Color Shift

Δ(u’v’) = 0.0106

2.7 JNCD  Very Good

JNCD is a Just Noticeable Color Difference.

See Figure 2 for the definition of JNCD.

Color Shifts below 3.5 JNCD are Very Good

Green Primary Color Shift

at a 30 degree Viewing Angle

Small Color Shift

Δ(u’v’) = 0.0079

 2.0 JNCD  Excellent

JNCD is a Just Noticeable Color Difference.

See Figure 2 for the definition of JNCD.

Color Shifts below 2.0 JNCD are Excellent

Blue Primary Color Shift

at a 30 degree Viewing Angle

Medium Color Shift

Δ(u’v’) = 0.0227

 5.7 JNCD  Good

JNCD is a Just Noticeable Color Difference.

See Figure 2 for the definition of JNCD.

Color Shifts 3.5 to 7.0 JNCD are Good.

 

Color Shifts for Color Mixtures

at a 30 degree Viewing Angle

Reference Brown (255, 128, 0)

 Small Color Shift

Δ(u’v’) = 0.0014

0.3 JNCD  Excellent

JNCD is a Just Noticeable Color Difference.

Color Shifts for non-IPS LCDs are about 10 JNCD.

Reference Brown is a good indicator of color shifts

with angle because of unequal drive levels and

roughly equal luminance contributions from Red

and Green. See Figure 2 for the definition of JNCD.

 

 

Display Spectra

The Display Spectra for the Auto, sRGB, and DCI-P3 Color Modes and for the Reading Mode are measured in Figure 5 below.

 

The Display White Point is Adjustable:

with the Reading Mode, Adaptive Colors Mode, and Interactive Touch Screen.

 

· The Reading Mode is designed to change the color balance of the display in order to reduce the amount of Blue Light

produced by the display, which some recent research indicates can affect how well users sleep afterwards.

The White Point can shift down to a Warm 4,020 K. See Figure 5.

 

· The Adaptive Colors Mode automatically changes the White Point and color balance of the display based on real-time

measurements of the Color of the Ambient Light falling on the screen. The idea is to make the display behave more like

paper reflecting Ambient Light and taking on its Color. It is implemented with an Ambient Light Sensor that measures

the Color of the Ambient Light in addition to its Brightness.

The White Point can shift between 4,900 – 7,050 K for the Original sRGB and DCI-P3 Modes, and 5,150 – 7,600 K for the Auto Mode.

 

· The Interactive Touch Screen in Display Settings allows the White Point to be chosen from a Color Map or Buttons.

The White Point can shift between 5,950 – 6,900 K for the Original sRGB and DCI-P3 Modes, and 6,700 – 8,300 K for the Auto Mode.

 

 

 

Figure 5

Display Spectra

Click to Enlarge

 

 

 

 

 

About the Author

Dr. Raymond Soneira is President of DisplayMate Technologies Corporation of Amherst, New Hampshire, which produces display calibration, evaluation, and diagnostic products for consumers, technicians, and manufacturers. See www.displaymate.com. He is a research scientist with a career that spans physics, computer science, and television system design. Dr. Soneira obtained his Ph.D. in Theoretical Physics from Princeton University, spent 5 years as a Long-Term Member of the world famous Institute for Advanced Study in Princeton, another 5 years as a Principal Investigator in the Computer Systems Research Laboratory at AT&T Bell Laboratories, and has also designed, tested, and installed color television broadcast equipment for the CBS Television Network Engineering and Development Department. He has authored over 35 research articles in scientific journals in physics and computer science, including Scientific American. If you have any comments or questions about the article, you can contact him at dtso.info@displaymate.com.

 

DisplayMate Display Optimization Technology

All Smartphone, Tablet, Monitor and TV displays can be significantly improved using DisplayMate’s proprietary very advanced scientific analysis and mathematical display modeling and optimization of the display hardware, factory calibration, and driver parameters. We help manufacturers with expert display procurement, prototype development, display performance improvement and optimization, testing displays to meet contract specifications, and production quality control so that they don’t make mistakes similar to those that are exposed in our public Display Technology Shoot-Out series for consumers. This article is a lite version of our advanced scientific analysis – before the benefits of our DisplayMate Display Optimization Technology, which can correct or improve all of these issues. If you are a display or product manufacturer and want to significantly improve display performance for a competitive advantage then Contact DisplayMate Technologies.

 

About DisplayMate Technologies

DisplayMate Technologies specializes in proprietary advanced scientific display calibration and mathematical display optimization to deliver unsurpassed objective performance, picture quality and accuracy for all types of displays including video and computer monitors, projectors, TVs, mobile displays such as Smartphones and Tablets, and all display technologies including LCD, OLED, 3D, LED, LCoS, Plasma, DLP and CRT. This article is a lite version of our intensive scientific analysis of Smartphone and Smartphone mobile displays – before the benefits of our advanced mathematical DisplayMate Display Optimization Technology, which can correct or improve many of the display deficiencies. We offer DisplayMate display calibration software for consumers and advanced DisplayMate display diagnostic and calibration software for technicians and test labs.

 

For manufacturers we offer Consulting Services that include advanced Lab testing and evaluations, confidential Shoot-Outs with competing products, calibration and optimization for displays, cameras and their User Interface, plus on-site and factory visits. We help manufacturers with expert display procurement, prototype development, and production quality control so they don’t make mistakes similar to those that are exposed in our Display Technology Shoot-Out series. See our world renown Display Technology Shoot-Out public article series for an introduction and preview. DisplayMate’s advanced scientific optimizations can make lower cost panels look as good or better than more expensive higher performance displays. If you are a display or product manufacturer and want to turn your display into a spectacular one to surpass your competition then Contact DisplayMate Technologies to learn more.

 

Article Links:  Display Color Gamuts Shoot-Out NTSC to Rec.2021

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Article Links:  Mobile Display Shoot-Out Article Series Overview and Home Page

Article Links:  Display Technology Shoot-Out Article Series Overview and Home Page

 

 

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