Picture of Quick Color Change
This is the fastest method I know for changing the color of something in a picture using GIMPPortable, or Photoshop. You make a hasty selection with the lasso tool, feather it, and then adjust the hue, using the option to adjust only the blues in the picture. This prevents unwanted color changes simply.

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Step 1: Make a Quick Selection

Picture of Make a Quick Selection
Open your picture in GIMP.

In my picture, I want the blue car to be green, but not the carpet, or anything in the background, so I need to roughly select the car.

Click on the lasso tool. Drag a quick selection around the car. Tweak the selection a bit using to add to the selection and to subtract from the selection. You do not have to be perfect with this. Not even close.

Great. Car selected.

Step 2: Adjust the Hue

Picture of Adjust the Hue
Go to Layer>Colors>Hue-Saturation

Select the blue swatch in the Hue Saturation window that pops up, and drag the hue slider around. Pretty good. Click OK.

Let us take a look at our picture without the crawling ants. Hit or go to Select>None.

Now I noticed a slight line on the floor near the selection edge. This is because there is a little blue light hitting the floor.

We can fix that by feathering the selection before adjusting the hue.

Step 3: Feather the Selection

Picture of Feather the Selection
Go back a few steps with or by going to Edit>Undo a couple times until you see the original picture with a selection.

Now go to Selection>Feather and change the value to, say 10 pixels. Click OK.

Adjust the hue again and look at your final picture. No line near the floor. Great.

Save your new picture.

Step 4: A Final Note

Picture of A Final Note
One final note on changing the hue of something in an image: In nature, some colors appear more saturated than others. So when you change a hue, tone down the saturation a bit to see if it looks more realistic.

So the steps again are:

1)Rough selection.

2)Feather the selection.

3)Adjust the Hue.

Happy shopping!
here mine hope you like it
derfman247 years ago
This is mine.
2006-Dodge-Viper-SRT10-SA-Top-Studio-1920x1440 green.jpg
glycerinate7 years ago
The first pic was red and the second was dark blue. these images were from google. GREAT INSTRUCTABLE!!!!!! you can do this on any computer with gimp portable!
my viper.jpgmy viper 2.jpg
royalestel (author)  glycerinate7 years ago
Hey, good job.
jinventive8 years ago
You could use this techniqe for background subtraction on still images.
royalestel (author)  jinventive8 years ago
How's that? I know of a few background subtraction techniques but one using a hue adjustment is news to me. Care to share?
Or maybe I was wrong I tried it later and it didn't work. Sorry :D
m-arijn8 years ago
nice to see how everbody uses your instructable for new instructables. but you can also download the normal version of gimp on www.gimp.org!!! it works alot faster!
royalestel (author)  m-arijn8 years ago
Who uses my instructables for new instructables? Anyhoo . . .I'm going to check out the new version of GIMP now.
asianwizard8 years ago
his bag is not green
hah, you misunderstand the effects of GI. or global illumination. If you look at the picture of the blue car, his bag is tinted blue thanks to the reflected light. He did this quite right, sorry asianwizard ;p.
royalestel (author)  ARVash8 years ago
You know, I didn't even notice the bounce light on the bag. Sharp eyes y'all!