[Digikam-devel] Adjusting filters to be deterministic

[Gilles Caulier]

2010/6/17 Marcel Wiesweg <marcel.wiesweg at gmx.de>:
>
>> JulienN raised a good idea in comments under my blogpost. Rewrite the
>> filters to be deterministic and thus fully reproducible. This would help a
>> lot for non-destruct. editng. I would go with leaving the random init part,
>> but alter the filters in such way, that we can store the output values and
>> reuse it later with those exact same values to get an exact same output.
>>
>> The benefits would be quite big for NDE as now the concept is such, that
>> with using any non-reproducible filter, new file must be created to
>> preserve this exact output and also, any edit you did prior that will be
>> unremovable without losing this output. Example: you use brightness,
>> contrast and raindrops and then some other filters. Now you see that the
>> initial brightness is not very good so you want to change/remove it. But
>> if you do so, you must reapply all the filters in the stack which are
>> after
>> brightness. But since you can't reapply the raindrops, you need to lose
>> this and that means you will lose any other edits you did after raindrops
>> too.
>>
>> What do you think? Would it be possible to alter all the filters so they
>> could be reproduced to get the exact same output? I don't have very good
>> code knowledge of them.
>
> Yes, it's a very interesting point.
>
> 1) Which filters are affected? A search for rand reveals:
> - BlurFX
> - DistortionFX
> - Filmgrain
> - Raindrop
> - localcontrast
> - in the CImg library
>
> I would separate out one group of filters: Those depending on very complex,
> possibly externally develop algorithms like CImg. For these, the algorithm can
> change with library updates, we dont have full control anyway.

CImg is included in digiKam. So the problem can be wrap around.

But... last CImg do not include GreyStoration algoritm now. a new
library have been developped and is named GMic... I already take a
look into this lib, and i lost. It's difficult to use with digiKam


> I am not sure which other plugins fall into this group; localcontrast? Gilles
> knows more about that.

I'm not sure to understand. Why localcontrast fall into this group. it
just a color correction tool as BCG, or HSL...

Gilles