On Apr 20, 2014 8:28 AM, "Tom Wilshaw" <[email protected]> wrote:
> I see what you mean now about the colour wheel. Is there a projected time for fixing this issue? https://developer.blender.org/T39707 > "The issue is that with scene referred data it is deadly tricky to calculate > the out of gamut values. " > > Could you elaborate on this? Is it because sRGB or REC.709 assumes things are normalised? If you down gamut a scene referred (0..infinity) image to sRGB / 709 primaries from a wider gamut, it isn't terribly easy to spot the out of gamut channels on the positive side without checking the transformed RGB values against max() and 0. My suggestion of normalizing the values is nothing more than an easier way to spot them; anything less than zero or greater than one. > "So is XYZ. If you look at ACES primaries sources dumped raw to sRGB, it looks equally wonk." > > It does, but code values are still rather more intuitive in ACES by virtue of it being RGB based. For example, a mid grey card, an inportant reference in visual effects, should read 0.18, 0.18, 0.18 in ACES. In XYZ, it reads 0.1715, 0.1800, 0.1816. 0.18 is a convention of course, and any RGB set could theoretically align in XYZ as you described (Warning: Guess math alert!) by normalizing your RGB white point to xy 0.333333 0.333333 via a Bradford. In a scene referred image of course, many grey cards may land at random value levels depending on whatever convention you implement. Value 103.1 is equally valid. Again, a single exposure data value of 0.18 for a grey card is a pure convention. > A move to XYZ would fulfill our own needs well enough for working with the cameras that we do, however it doesn't seem like the best long term decision for Blender itself. ACES is an open standard which is set to become increasingly common. Blender might do better to be ahead of this trend, rather than effect a move to XYZ only to have to move to ACES at a later date in order to satisfy users in these fields. The issue is that ACES _currently_ does not easily fulfill the broad range of needs. Deviating from the specification would effectively negate the upside of the standard. All we can do is wait until either ACES evolves further. Until that time, in my estimation, it is a sub-optimal decision. XYZ on the other hand, is going nowhere and is a universal standard as well, so _if_ there is a debate about internal representations, it is not entirely without merit. It is perhaps the first de facto open standard in color. > Do you think it would be worth trying to gather the opinions of other users who use Blender for visual effects or postproduction (or even animation)? We might start a Blender Artists thread and see what a few other people think? Many artists don't follow the mailing list. My experience is that the color theory discussions on BA have resulted in underwhelming participation. Color still confuses the heck out of folks, and can be an intimidating topic. It certainly is for me. With respect, TJS _______________________________________________ Bf-committers mailing list [email protected] http://lists.blender.org/mailman/listinfo/bf-committers
