On Mon, 3 Jul 2017 19:11:46 +0200 Mattias Andrée <maand...@kth.se> wrote:
> On Mon, 3 Jul 2017 18:55:42 +0200 > Laslo Hunhold <d...@frign.de> wrote: > > > On Mon, 3 Jul 2017 18:47:37 +0200 > > Mattias Andrée <maand...@kth.se> 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. > > Yes. However, if this is not done, the error is probably less than if > multiple edits have been made to the image without considering this. > > > 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. > > That was just an example to illustrate how manipulations should be > applies. And indeed it is not common that you need exact changes. > If you need exact colours you probably don't want to use farbfeld > at all because it is restricted to colours in the sRGB gamut. > > To avoid the problem with the transfer function, it is probably > enough (since farbfeld uses 16-bit values) to add a tool applies > the inverse transfer function and a tool that applies the transfer > function. That way, the editing tools can be as simply as they are > today, but you can get rather exact results if you need it. I think some tools must still be aware of sRGB's non-linearity. For example, if you make a tool that draws a gradient, you probably want the colours in the gradient to increase linearly, so you have to be that the colour model is not linear. > > > > > With best regards > > > > Laslo Hunhold > > >
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