On Mon, 3 Jul 2017 19:11:46 +0200
Mattias Andrée <maandree_AT_kth.se> wrote:
> On Mon, 3 Jul 2017 18:55:42 +0200
> Laslo Hunhold <dev_AT_frign.de> wrote:
>
> > On Mon, 3 Jul 2017 18:47:37 +0200
> > Mattias Andrée <maandree_AT_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
> >
>
Received on Mon Jul 03 2017 - 19:29:41 CEST