Brightness, Black Level, Contrast Ratio, And Gamma
Brightness
Brightness (also known as white level) measurements are taken by recording the luminance output of each device displaying a full white pattern, with the device's brightness slider set to both minimum and maximum values.
HTC's One (M8) has a high minimum brightness level, though it looks downright fantastic next to the Lumia Icon's three-stage brightness selection range. Separately, I've heard that an upcoming update to Windows Phone will address this with more configurable controls. In any case, the One (M8)'s maximum brightness level is second only to Apple's iPhone.
In order to make device comparisons possible, the rest of our display measurements (along with our battery testing) are performed with the screen set to a standardized 200 nits.
Black Level
Our black level measurement reflects the reading of a full black pattern after dialing in our 200-nit brightness. AMOLED displays always register zero, since their pixels simply turn off to render black. That's why the Galaxy Note 3 and Lumia Icon don't appear on our chart.
Traditionally, Samsung's AMOLED-equipped devices dominate, since AMOLED displays offer the best black levels. HTC's One (M8) delivers the best non-AMOLED result, though.
Contrast Ratio
Contrast ratio is the difference between a full white and full black patterns. Due to their zero reading on the black level tests, AMOLED displays are said to have an infinite contrast ratio.
The outcome isn't surprising, then. But HTC's One (M8) does perform excellently, demonstrating one of the best black level/contrast ratios we've seen from an IPS-based screen.
Gamma
A gamma curve of 2.2 is what we're looking for. The reason for this is that images captured in the sRGB color space are encoded in a gamma of about 1/2.2. A gamma curve of 2.2 allows the resulting images to be viewed at the ideal brightness and contrast.
The One (M8) falls shy of an ideal gamma reading, which could be surprising after seeing how much attention went into the exceptional black level and contrast.
Color Temperature
Color temperature is a measurement in Kelvin, which is used to describe how “warm” or “cool” a given display is. Ideally, as long as you're not viewing your device in direct sunlight, this should be in the 6500 range. Higher color temperatures result in a cool, bluish hue, while lower temperatures deliver a warm or reddish tone.
HTC's One (M8) appears in the middle of the pack. It's cooler than we'd like, but only one position away from Apple's lauded iPhone 5s, too.
Color Gamut
Our volume measurements are compared against both the sRGB and AdobeRGB color gamuts. A reading of 100 percent on sRGB and 72 percent on AdobeRGB is the optimal reading for viewing the vast majority of digital consumer content. A lower reading is typically accompanied by an overly red or yellow image, and a higher reading is usually too blue/green.
HTC's One (M8) does well in this metric, approaching the gamut volumes we'd like to see.
