HDR, color management, krita, luts and other apps

[Boudewijn Rempt]

On Wednesday 06 June 2012 Jun, Sven Langkamp wrote:

> I guess someone would get shot for the first sentence in Simon's place ;)
> Would be a bit strange if an application that costs a few thousand euro
> couldn't do that.

Er, no -- I think that Nuke users are supposed to assume that their monitors are all sRGB without serious deviations. That's a workflow that Krita will support, of course, by setting the monitor profile to sRGB.	

<...>

> I think you need to do more than just the lut docker. The image would have
> an ocio colorspace and we can't convert between icc based and ocic easily.
> 
> To make that easier we might limit the layer colospace to the image
> colospace to avoid conversion on lower levels too.

I'm assuming that any layer-internal colorspace conversions aren't relevant here. Down to the projection composition it's all lcms2. From there, I want the lut docker to enable some optional extra steps that replace the usual projection-to-monitor tranform:

* associate the projection with an ocio lut. I don't want to convert the projection using ocio, I want to disregard the existing colorspace. This will only work for float32 rgba color models, of course -- ocio supports nothing else in any case.

* implement the functionality of the mari toolbar in the lut docker

* implement the transforms from the image projection to 8 bit sRGB using ocio

* (optionally) use lcms2 to convert sRGB to the monitor profile (if different from from sRGB).

> Just if Krita is running in ocio mode, lcms would still need a shader or so.

There's existing code (in oyranos) that allows us to create a lookup texture from an icc profile, so the last transform (sRGB->monitor) can also be done in a shader.


> I think if you go with lcms->ocio->lcms, that defeats the whole purpose of
> using ocio in the first place. I think we could just assume that somebody
> who uses ocio will use opengl canvas.

Well, not, not quite, the purpose of ocio is to allow the familiar transforms (lut changes, gamma, exposure, channel selections). That can work in the qpainter canvas just as well.

In fact, I intend to implement it in the qpainter canvas first, since the opengl canvas is in a bit of a flux at the moment. 


-- 
Boudewijn Rempt
http://www.valdyas.org, http://www.krita.org, http://www.boudewijnrempt.nl