Select-by-Color, A GIMP Tutorial…

As promised, a GIMP* tutorial for the image I did for the One-Four-Challenge-January-Week-1 (the Photoshop Tutorial can be found here).

*** Don’t Panic ***

*** I am a visual learner and have lots of screenshots, don’t let the length of this tutorial scare you. ***

My original raw image had a bit of a blown out sky, after trying to fix this in a raw editor, I had a blue edge to my leaves.  This is a tutorial to remove those blue edges.

The concepts here can be used for other applications as well, you are only limited by your own imagination. 😀


First, let me give a primer on selecting an area using the select-by-color tool… then we will move on to putting it all together to achieve what I have done in the image above.

Select-by-Color Primer

I suggest you duplicate the layer you are wanting to select from Shift-Ctrl-D, that way you can always go back if the need arises.  For the tutorial that follows, it is imperative that you have the original image as a background and each layer is stacked on top (you will be making many duplicates of that background layer).

select-by-color-toolThe select-by-color tool allows you to pick a color to select.  You can refine this selection by grow/shrink or even feathering out the selection area.


You can also add to your selection by changing the mode (reddish square icons), change the threshold level of the color being selected and much more…


Once you have your selection, add a mask layer… Layer->Mask->Add Layer Mask… click the radio button for Selection


You can invert the mask as you make it by clicking the button beside Invert mask… or you can invert it later by going to Colors->Invert

Deselect the marching ants by Shift-Ctrl-A.

Ok… Now that you have the basics, let’s get to the tutorial for this image…

GIMP Tutorial

I have created this little shortcut ‘post-it’ for quick reference…


Fix Blue Leaves Tutorial – Quick Glance:


  1. Duplicate base layer, select-by-color sky area, create mask (invert mask), fill with dark green, change blend mode to Color
  2. Duplicate base layer, select-by-color light green area, create mask, fill with light green, change blend mode to Color
  3. Duplicate base layer, add mask, paint in areas that need original color – tree trunks, foreground leaves
  4. Duplicate dark green layer, invert mask, fill with blue, change blend mode to Multiply

Detailed Notes:

1. Follow the select-by-color primer above… selecting the sky color and creating a mask layer… (base layer visibility has been turned off in the image below to show the masked layer).  Invert the mask by selecting the mask icon on the layer and then going to Colors->Invert


color-picker-toolPick a color from one of the dark leaves by using the Color-Picker-Tool.

Alternately, click on the foreground color block and change the color by setting the HTML notation to a known color.


Then fill the image with this color (NOT the mask) by clicking on the image icon and then going to Edit->Fill with FG Color, set the blend mode to Color


2. Duplicate the base layer then move it to the top of the stack…


This time select-by-color the light green leaves, I made sure that I had the tool mode set to add to selection (the icon that looks like two reddish squares on top of each other) and chose several different areas of light green…



Create a mask, fill with light green and change the blend mode to Color


3. This time duplicate the base layer and move it to the top of the stack, but instead of making a selection, only create a mask of black (black conceals, white reveals)… Layer->Mask->Add Layer Mask… click the radio button for Black


paint-toolThen use the paint-tool [P] and paint white on the black mask in the areas that you want the original color to reappear.

Also I wanted to note that you can change the paint-tool brush size by clicking on the area in the tool-options dock… if you wiggle the mouse over the size area it will change from an up-arrow to a two-pointed-arrow. The up-arrow will allow a big change in size, thus you can get to work faster — I prefer this method.  You can also hold down the square brackets [ ] but that change is very slow and can be frustrating.


It will look something like this…step3-screen
4. You could stop here, but I wanted a bit more oomph to my sky, so I duplicated the dk green layer, inverted the mask, filled it with the same blue that sky was currently, then adjusted the blue by playing with the color (added saturation)… or you could set the HTML notation to a known color.  Then set the blend mode to Multiply


And that’s it!


I hope you enjoyed this tutorial… I know it seems like a lot… but once you get the basic idea you just keep repeating it in different ways until you get the final image.  I do hope you try these concepts out.

Until next time…

* GIMP is Open Source software that is available for all platforms (Linux, Mac, and Windows), it is a photo editor that does many (if not all) of the things you can do in Photoshop.  You can download it for free here.  The GIMP online manual can be found here.

2 thoughts on “Select-by-Color, A GIMP Tutorial…

  1. Thank you for taking the time to post this tutorial but it still sounds overwhelming to me. I will have to sit down with a print out of this and a download of GIMP to figure it out!

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