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No matter how new or old your slide is, your scanner will scan the gloss that comes off a slide.
This leaves you with flat, faded colours. Yes, time also fades colour. But the biggest issue is the scanning process itself -- it's not perfect.
To get rid of this without touching any of the real colours of your image, do the following...
GIMP > Colors > Auto > White Balance
What you're doing here is getting rid of the glare that your scanner picked up during the scan.
In other words, you BALANCED all the colours. And that flat look is now gone.
Now you can start to brighten and heighten the colours. Here's how...
Once you got rid of the glare, you can begin to brighten the colours. Go...
GIMP > Colors > Hue and Saturation
What you did here is, saturation brightens all the colours in one easy step.
To use Saturation, move the slider to the right, just a bit. I went to 19, but you adjust accordingly. Don't saturate too much, though. The colours will look "plastic".
Lets see a before and after...
Before GIMP colour fix -- colours look funny (blue looks purple) and the image is flat because of the glare off your slide film.
After GIMP colour fix -- colours look natural, and you got rid of the glare that made your scan look flat.
To make the colour pop even sharper, brighter, and more defined, you need one more step. You need to fix the exposure. Once you do that, then you'll see a huge difference.
Check out more free slide scanning tips below...
Here's those full tutorials again...
Step 1: Fix Dull, Flat, Unnatural Colours Using GIMP
Which of these scanning troubles do you want to overcome?
Hey, my name is Konrad. I've been scanning professionally since 2005. I've helped multi-billion dollar companies, pro sports teams, pro photographers, artists, museums, book publishers, etc. I've scanned over 930,000 slides, negatives, photos.
The reason I'm telling you this is because no matter what challenge or frustration you're having, I know exactly what you're going through. So, to help you RIGHT NOW, I've put together a super simple scanning guide to get you started.