[digiKam-users] Fwd: Hope this is not OT

[Sveinn í Felli]

Þann 12.5.2021 17:48, skrifaði Errol Sapir
> Hi Gilles
> 
> The idea isn't to invert colour but to enhance colour. The slides have faded and
> the original colours aren't alive. The link shows a photo that has faded.
> 
> Errol
> 
> https://mega.nz/file/QxlEAIbI#gwt5Omb5cSa1-WPeDxVlTdtyoNkwZYdeUC9xVp9L6b4
> 

Hi Errol,

Scanning and repairing old slides can be a complex matter; it depends on 
brands of film, on previous storage of the slides, and on type of mount 
(what kind of frame they've been mounted in), and possibly other factors 
too.

I've repaired several slides similar to the one you shared, guess this 
one is an AGFA-GEVAERT positive film, possibly a FUJIFILM. Sometimes a 
generic automatic filter like "Equalize" will do the trick; problem is 
that often a great deal of image info will be lost. Other problem is 
that usually not all the original photos were ever "correctly" exposed.
Existential problem; do you want to be faithful to the original images 
or just get decent usable photos right away?

I searched the web thoroughly for info on how to do this with 
FOSS-software; there are some scripts (mostly for GIMP) for certain 
types of film of certain age (yes, the year of production counts), but 
the majority of those doing such work resort to using the commercial 
extensions available for Photoshop. Those are sort of databases with 
measured decay of various types of film, along with commands for 
corresponding filters.

Nevertheless I found a neat procedure for doing this in GIMP (can't find 
the source right now); Take one of a batch similar slides (from one 
shooting, one year or similar exposure), demount it from the plastic 
frame (bad luck if it's glued into a paper frame) and scan the whole 
area, including the perforated strip on both sides, where normally there 
should be markings in clear letters with the brand name and number of 
the image.

In "Levels" histogram mode with the eyedropper-tool in "All channels" 
section, change the white-point to a decent sample of a letter on the 
strip (transparent = white), similarly take the black-point from the 
surrounding black/opaque frame, then pick a gray-point (where a gray 
area should be) from the image itself. This way you're compensating for 
the "natural" decay of the corresponding film (of a certain brand, 
certain age). You may then have to fiddle with all the color-components 
separately to further enhance colors. The most important is to save the 
result as a preset, and then use that preset manually on each image 
(with further enhancements like sharpening etc.) or use it on several 
images with GIMP --headless on the command line.

You could also use the values from this preset to make settings for the 
BatchQueue Manager in Digikam or some script for ImageMagick.

But as stated above, this procedure only compensates for the natural 
decay of the film itself, not the decoloration of the image due to 
sunlight or overuse (number of passages in a projector).

For those who like the technical side of things: 
<http://www.lionhouse.plus.com/photorestore/Restore2.pdf>

Good luck,

Just some thoughts - good luck restoring your slides,
Sveinn í Felli


> On 12/05/2021 11:50, Gilles Caulier wrote:
>>
>>
>> Le mer. 12 mai 2021 à 04:39, Errol Sapir <errol at tzora.co.il 
>> <mailto:errol at tzora.co.il>> a écrit :
>>
>>     Hi All
>>
>>     I am now trying Manjaro KDE after many years of Kununtu. Of course I am
>>     also planning to transfer (or redo) my Digikam from Kubuntu to Manjaro. I
>>     have however a photo question that doesn't specifically apply specifically
>>     to either of these programs. As I said in the subject I hope it isn't OT
>>     but as it is photo connected and I hope Digikam can help as well I would
>>     appreciate the help of anyone who can. If it is OT the moderators can
>>     remove my post and I will understand.
>>
>>     I am transferring all my slides (and eventually negatives) to digital
>>     format. I am looking for a one-click solution (program) that will restore
>>     colours back to normal.
>>
>>
>>
>> You want mean to invert color ? If yes, ImageMagick is your friend, especially 
>> -negate option:
>>
>> https://superuser.com/questions/1194468/invert-colors-with-imagemagick
>>
>> This can be scripted of course to parse and process automatically all files 
>> from your collection. And of course, all can be done de facto under Linux from 
>> command line.
>>
>> Else, In digiKam, Invert Color tool from Batch Queue Manager can be used. 
>> Create a new Queue, assign items to process, configure the output options 
>> (path, file name, etc...), assign Invert tool + the convert format if 
>> necessary, and... you can take a coffee.
>>
>> Best
>>
>> Gilles Caulier
>>
>