Re: [dev] Problems with farbfeld image editing tools

From: Laslo Hunhold <>
Date: Mon, 3 Jul 2017 18:55:42 +0200

On Mon, 3 Jul 2017 18:47:37 +0200
Mattias Andrée <> wrote:

Dear Mattias,

> Perhaps farbfeld should specify that it should use linear sRGB, right
> now it specifies sRGB, which implies non-linear. It wouldn't make
> the format less complicated in my opinion, but it would be easier to
> implemented editing tools.

It would make it easier to implement the tools, however, this would on
the other hand force everybody trying to display farbfeld images to
make the transformations back to non-linear sRGB.
As you already explained pretty well, the non-linear gamma curve is
there for a reason.

> The problem with treating non-linear colour models as linear is that
> the error accumulate. Whilst you may not notice the error after one
> edit unless you compare the image to the correct one, it will be
> noticeable if you apply multiple change.

This is correct, but only applies to cases where we need "exact"
transformations. Every non-integer arithmetic operation has the
potential to be erroneous. Given we have 16 bits per channel, the
accumulated error would be invisble in most cases, even for long
pipelines (if you don't do anything crazy).

> 50 % bright in the linear model is at 0.50, but at 0.74 in the
> non-linear model. The difference is almost 50 %, the difference is
> larger at darker colours.

When was the last time you needed to brighten up your picture by
"exactly factor 2"? Most of the time, people open GIMP and move the
slider until the brightness suits their taste.

With best regards

Laslo Hunhold

Laslo Hunhold <>
Received on Mon Jul 03 2017 - 18:55:42 CEST

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