Ultra HDR (High Dynamic Range) is an image format that utilizes improved implementation of existing HDR technology to enhance the visual perception of photos on HDR displays via a luminance modulation technique called gain mapping which reallocates pixel intensity on a per-pixel basis based on its spatial factors. This format was engineered by Google in 2023 and first deployed on the Android 14 operating system.^[1]

Ultra HDR format is an enhancement of conventional HDR, where gain mapping technology allows further pushing the boundaries of existing HDR. However, not all displays can render the full capabilities of HDR and Ultra HDR formats. To overcome this issue, a tone mapping technique is used to adjust the brightness and contrast to match the quality of capable displays. HDR has the capability of recording a much wider color gamut in comparison to a traditional 24-bit RGB (SDR). Ultra HDR takes a step further, improving the visualization of the image. Moreover, it has a wider range of tones and subtle gradients, reaching the limits of the Rec.2020 color space, and providing a much wider spectrum than HDR10’s DCI-P3.^[2][3]

The distinctions in between SDR, HDR and Ultra HDR can be can be evaluated using the equation, where Color Volume is used as a metric for the range and richness of colours that each format can show. ^[4] ${\displaystyle {\text{Color Volume}}=\int _{\text{Color Space}}\left(L(R,G,B)\times C(R,G,B)\right)\,dR\,dG\,dB}$

Where:

• L(R,G,B) represents luminance function across the RBG colours.
• C(R,G,B) represents coverage function, which captures a color gamut boundaries and bit depth.

• dR represents differential of Red variable R, change in the red channel's intensity
• dG represents differential of Green variable G, change in the green channel's intensity
• dB represents differential of Blue variable B, change in the blue channel's intensity

Representative values are as follows:

• Luminance: 100 nits.^[5]
• Chromaticity: 16.7 million colors (sRGB color gamut).

Color Volume_SDR ≈ 1.67 billion

Referring to the calculation of Color Volume, we obtain an approximate value of 1.67 billion across the color space, representing 1.67 billion possible colors variations on RBG Model.

Representative values are as follows:

• Luminance: 1000 nits.^[6]
• Chromaticity: 1 billion colors (DCI-P3 color gamut).

Color Volume_SDR ≈ 1 trillion billion

Referring to the calculation of Color Volume, we obtain an approximate value of 1 trillion over the color space, representing 1 trillion possible color variations.

Representative values are as follows:

• Luminance: 4000-1000 nits.
• Chromaticity: ≥1 billion colors (DCI-P3 color gamut).

Color Volume_SDR (taking 4000 nits as luminance) ≈ 4.28 trillion billion

Referring to the calculation of Color Volume, we obtain an approximate value of 4.28 trillion over the color space, representing 4.28 trillion possible color variations.

V_{Ultra HDR} > V_HDR > V_SDR

Based on the previously expressed formula, the mathematical comparison can be seen in terms of Color volume capabilities.

• High Dynamic Range
• Brightness
• Image contrast
• Gamut
• Gain map
• Color volume
• sRGB

• Gain Mapping
• High Dynamic Range Television System
• Future of Photography- Ultra HDR, Google