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

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

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

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