In contradiction to what you might assume, the Canon DSLR cameras video conforms to the ITU-R BT.601 standard for SD video recommendations, instead of the ITU-R BT.709 HD standards. This means that several suppliers of software for video- and film-makes try to convert the color decoding matrix of the Canon DSLR video footage. An example is the new 5DtoRGB software that assumes (in it’s helpfile) that the Canon 5D (1D/7d/550d/T1…) uses the ITU-R BT.601 color decoding matrix (“Primary chromaticities”). THIS IS NOT THE CASE!
Canon conforms to the ITU-R BT.601 standard, but NOT in regard to the “Primary chromaticities”. The Canon DSLRs exclusively use the sRGB color space for video, which shares the ITU-R BT.709 primaries. So, no color space conversion or matrix conversion is needed for Canon DSLR video footage and ITU-R BT.709 should be maintained throughout the workflow as “Primary chromaticities”.
Confused?! Read on..!
In order to convert the “real world” colors recorded by the camera’s image sensor to electric (and digital) signals, the camera uses a Decoding Matrix to “map” colors to numbers. All digital cameras do this and the broadcast industry has provided several standards to the camera manufacturers, to make sure (this was the idea…) red is red and blue is blue… and sixpence is sixpence… So we ended up with tons of “standards”.
These standards are laid out in several ITU-R recommendations. They don’t only describe decoding matrices (“Color space” or “Primary chromaticities”), but also Pixel count, Frame rate, Digital representation, Standards Conversion, Luma coefficients and Transfer characteristics.
Manufacturers, leading broadcasters and standards institutes (i used to work for one…) flooded us with recommendations and Decoding Matrices that the industry and video producers should adhere to. With the age of digital HD video came a few new ITU-R standards that are generally in use for digital video cameras:
- ITU-R BT.709 recommendation -standardizes the format of high-definition television, having 16:9 (widescreen) aspect ratio
- ITU-R BT.601 recommendation – mainly used with SD images and Canon DSLR video having 4:3 or 16:9 (widescreen) aspect ratio
Primary chromaticities
BT.709:
CIE 1931 xy chromaticity diagram showing thegamut of the Rec. 709 color space and location of the primaries. The white point is shown in the center.
| Color space | White point | Primaries | ||||||
|---|---|---|---|---|---|---|---|---|
| xW | yW | xR | yR | xG | yG | xB | yB | |
| ITU-R BT.709 | 0.3127 | 0.3290 | 0.64 | 0.33 | 0.30 | 0.60 | 0.15 | 0.06 |
Note that red and blue are the same as the EBU Tech 3213 primaries while green is halfway between EBU Tech 3213 and SMPTE C.
The trained eye can see from the chromaticity diagram above that the ITU-R BT.709 decoding matrix (“color space” or or “Primary chromaticities”) is equal to that of the sRGB color space used by the Canon (video) DSLR cameras. The images are from different sources and are only here for illustration; it’s the numbers that count of course.
So, why do Canon DSLR cameras use the BT.601 recommendation for SD video, instead of the BT.701 recommendation for HD video, while using the latter’s color space?! The answer is simple… The Canon DSLR video can not comply with the BT.701 recommendation in regard to frame rates and maybe even pixel count (read the BT.709 specs via the link above)! Canon DSLR cameras can not be considered HD cameras following the BT.701 recommendation and that might also explain why broadcasters such as the BBC do not accept Canon DSLR footage for HD broadcast as such.
Hope that answers some of the questions i’ve received by mail the last few weeks.
Kind regards.
Jorg Escher
Jorgen Escher 