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Saturday, December 13, 2014

Interpreted tutorial for fixing exposure and remove color cast and to fix blemishes

3:22 PM Posted by SnowSews
Rita, of TheCoffeeShopBlog has a brilliant, free tutorial on fixing exposure and removing color casts from a free photo of a lovely little model. Go see her tutorial here. I don't have Photoshop, which her tutorial is written for, but with a little patience and a lot of Google, I translated her Photoshop tutorial into GIMP. There are many differences between Photoshop and GIMP, the main one being that there are no actions in GIMP. In Photoshop, there are predefined, user created actions that are available (tons for free on TheCoffeeShopBlog) that perform complex tasks for you. I will be investigating how to translate those actions into GIMP as well, in the following tutorials.



From TheCoffeeShopBlog, I will be quoting her tutorial, and then giving succinct directions for GIMP. I do not take credit for anything written in italics, it's all Rita's hard work. 

Here is the before picture, found on Pixabay



"1.  Fix Exposure:  There are many ways to adjust the exposure of an image, and today I will show you how I do it using a level's adjustment layer.  As you can see from the screen capture above, I added some shadow (black slider), lightened the mid tones (gray slider), and brightened the highlights (white slider). 

Moving the sliders under the start of the curve on the left and right will usually add a nice boost of contrast to your image. Then move the middle slide to the left to lighten the mid tones and to the right to darken the mid tones.  This has to be adjusted for each image."

GIMP: Colors > Levels> Channel: Value, adjust the three input sliders to get desired effect

" 2. Remove Color Cast:  After adjusting the contrast I could really see that this image has too much red and yellow.  If you can't easily tell what color cast you are dealing with but know the image is "off", it is easy to play around with a level's adjustment layer until you get a nice skin tone. 

I added a new level's adjustment layer on top and selected "Blue" from the pull-down menubar.  If you add blue you remove yellow (you don't have to trust me on this one, play with the sliders to convince yourself).  I removed some of the yellow from the mid tones by  moving the middle (gray) slider to the right.  I also added a bit of blue to the shadows (black slider)."

GIMP: Duplicate previous layer, the one with exposure fixed. GIMP does not have adjustment layers.
On the new layer, select Colors > Levels > Channel: Blue as above.

"I used the same level's adjustment layer and selected "Red" in the pull-down menubar.  I removed some red from the mid tones (moved the middle slider toward the right).  Now I see a bit of green tint.  Argggh."

GIMP: Same dialog, Channel: Red, move middle slider to right.

"I selected "Green" and moved the middle slider a tiny bit to the right to reduce the green in the mid tones, and then added a tiny bit of green to the shadows.  Just eyeball these settings as you make the adjustments.

There is still a bit of red tint that is irritating me.  I know this seems like a lot of adjustments, but it only takes a minute or two at the most. "

GIMP:  Same dialog, Channel: Green, middle slider to right

"I selected the "Red" again and moved the middle slider from 0.84 down to 0.75 to reduce the reds in the mid tones.  Now I am pretty happy with the skin tone colors. At least for now.  ;-)"

GIMP:  Same dialog, Channel: Red, middle slider moved if necessary.

"This is something you will have to experiment with on your own images to get that perfect skin tone color.  Don't be afraid to play around with the sliders under the curve.  And make sure your monitor is calibrated."

"3.  Fix Blemishes:  There are many ways to fix blemishes on portraits, but I wanted to show you my favorite "quick and dirty way" to do it.

As you can see in the screen capture above, this adorable girl has a scratch under her right eye and a bit of skin discoloration under her left eye. 

Flatten your image after adjusting the exposure and color, and make a new layer over the background.  Use the eyedropper tool (I) (set to 3x3) and click on an area of clean skin around the reddish area.  Then select your brush (B) set at 0% Hardness and 20-30% opacity and click on the discolored areas until you remove them.

If you add too much skin tone paint you can erase it from the new layer and start over.  I often find this "painting" method works better than the patch or clone tools.  Don't worry too much about preserving all of the detailed skin tone as we are going to soften the skin some in the next tutorial."

GIMP: Layers: Merge down, duplicate layer. Select eye dropper tool (shortcut O), click on clean skin area. Select brush (shortcut P), set hardness to 0% and opacity to 30%. Paint over blemish in zoomed mode. This looks amazing.

This is my final image after following her tutorial in Gimp as described.