If I scan black and white lines, it usually works out fine, but watercolours never come out right; the images always look very bleached loosing all the vibrancy of the original. I asked other illustrators what they do, and here’s the answers I got:
I scan my watercolour (using Vuescan usually at 300 dpi); then adjust in Photoshop using Curves. I find for RGB that I need to increase below the diagonal; and for CYMK I need to increase above the diagonal. This gives me results that whilst not identical to my original watercolours, do have qualities that I like and print well. – Clare Tovey
… and from Lorna Eynsham:
Increasing Colour Range in Photoshop
• Scan image at least 300dpi. This will not work well if you have painted on
very textured paper.
• Open in Photoshop and create a new adjustment layer. (Layer > New Adjustment
Layer > Levels).
• Adjust the middle slider so the mid tones look right. Pale areas will bleach
but this is fixed later.
• Adjust the darks.
Click on the thumbnail of the level adjustment layer. Should have a white
outline if selected.
• Open Apply Image tool (Image> Apply Image).
The layer mask thumbnail will look like a film negative.
• Duplicate the darks layer, select layer mask and then invert.
• Now double click “Levels icon’ in the light layer to open levels tools.
Adjust the middle slider to the lights are good.
• Create a brightness/contrast layer. (Layer> New Adjustment Layer>
Brightness/Contrast) Increase Contrast and put this on the top layer.
• Duplicate original background layer and move to the top of the layers. Adjust
opacity of layer to suit.
These are the simplest steps I know to improve the colour range and I hope they
make sees to you. However, like all recipes, adjust to suit. The best source of
information is this index site;
which I heartily recommend. It was here that I found the best way of getting rid
of a colour cast in an image etc.
All the best