Re: [Gegl-developer] [Gimp-developer] babl roadmap

[Elle Stone <ellestone ninedegreesbelow com>]

On 10/15/2014 08:30 AM, Øyvind Kolås wrote:
> On Wed, Oct 15, 2014 at 2:11 PM, Elle Stone  wrote:

> > Will all color-managed image editing be done using the user's chosen
> > primaries, with absolutely no conversions to unbounded sRGB for image
> > editing?
> >
> > Or are the developers committing themselves to maintaining lists of which
> > operations should be done using fooRGB primaries and which should be done
> > using sRGB primaries?
>
> There is no plan to maintain lists in the end, this information would
> be self-contained within each individual operation,

If each individual operation will carry information about whether the 
operation should use fooRGB primaries or sRGB primaries, then at some 
point someone must compile a list for the devs to consult.

Unless you really mean to say:

*DevA working on Op1 decides whether to use fooRGB primaries or sRGB 
primaries for Op1.

*DevB working on Op2 decides whether to use fooRGB primaries or sRGB 
primaries for Op2.

*DevC can decide DevA and DevB were both wrong and change the code.

And so on.

Consider the following:

1. RGB editing operations performed on fooRGB images using fooRGB 
primaries are *always* correct.

2. More than half of all operations on linear RGB are 
chromaticity-dependent. Many more than half of all operations on 
perceptually encoded RGB are chromaticity-dependent. *All* of these 
operations WILL produce *wrong* results after the image is converted to 
unbounded sRGB.

So the developer choices are:

1. Either don't convert fooRGB images to unbounded sRGB for *any* RGB 
editing operations. Results will *always* be right.

2. Or else compile a list of all editing operations that "do work" and 
"don't work" in unbounded sRGB, and only convert the image to unbounded 
sRGB for the operations that "do work" in unbounded sRGB. And hope you 
get the list right, because you are messing with the user's RGB data for 
no good reason.

I will ask again:

For which specific RGB editing operations do you plan to convert the 
image from fooRGB to unbounded sRGB before performing the operation?

Either the answer is "None. For color-managed fooRGB images, all RGB 
operations will be done on data encoded using fooRGB primaries."

Or you are committing the devs to maintaining a formal or ad hoc list of 
operations on fooRGB data vs operations on unbounded sRGB data. And then 
you are committing the devs to writing per op code to implement entirely 
pointless conversions from fooRGB to unbounded sRGB and back again.

With respect,
Elle Stone