8-bit coding space limitations
The inherent problem with 8-bit encoded image data is its lack to store enough color values to accurately represent subtle tonal gradations. 8-bit means 255 distinct values for each of the R, G and B channels.
By transforming linear RAW sensor data to a logarithmic curve and thereby further compressing the range to even less values, all tonal gradation in the 8-bit coding space is sacrificed.
Chroma banding and severe image degradation are often the result when color grading logarithmically encoded 8-bit comressed footage back to a regular Rec709 or sRGB viewing gamma.
Comparison chart:14-bit linear RAW sensor data to
- 12-bit losslessly compressed ProRes (Arri LOG-C encoded) - 4096 values
- 8-bit h.264 compressed video (Cinestyle) - 150 values
- 8-bit h.264 compressed video (VisionColor) - 255 values
It is therefore recommended to shoot with camera profiles which utilize the entire 8-bit tonal range while preserving as much usable dynamic range and color information the image sensors have to offer. Subtle adjustments in post production are key to retaining image fidelity.
While the VisionColor profile utilizes the entire tonal range available in the 8-bit coding space, clipping at 0 and 100% IRE (RGB 0-255) VisionTech performs a slight boost of the blackpoint to 3% IRE. (RGB 9-255).
This enables the camera to encode hue and saturation information where in other profiles no such data could be encoded due to a luminance value of 0. (Black can't hold color values)
In video compression schemes, chrominance data is processed separately from luminance to exploit the limited resolution of color over relative brightness perception in the human visual system. However as our ability to accurately distinguish between subtle luma differences falls roughly into the range around 'middle grey' (18% reflectance) and gets worse as brightness drops, compression algorithms assign less data to the lower parts of the gamma range.
An estimated luminance/data-compression correlation of the h.264 codec has been taken into account for the lift adjustment of the VisionTech curve to prevent any negative side effects like chroma banding and other poterization artifacts that are commonly introduced in the midtones and highlights by profiles from other developers due to poor data distribution across the luminance range.
Dual Illuminant Profiling
All of our camera profiles are dual illuminant camera profiles. This means that your camera will automatically interpolate between two distinct transform tables, one for daylight temperature, one for fluorecent, based on your white balance setting. The method used by Canon internally is inverse correlated color temperature.