Very often I find that my cell phone photos have a grey wash to them or they just look flat in color. So, I use the Levels adjustment tool in Gimp to fix them. There’s lots of discussion about what levels are and what they do, etc. but I tend to focus on the practical. I simply adjust them until it looks right.

Open Gimp and then open an image you want to try this out on, preferably a photo that needs correction and/or has a grey wash to it. If you need an image to practice on, you can download this one.

Within Gimp, on the Image’s menu bar, select Colors | Levels and this dialog box will open up.

Notice the granular adjustments you can do, however correcting most photos I’ve found can be done with just pulling in the slider triangles from each edge to the beginning of the color levels for each photo/image, like so:

What’s nice about this tool, and Gimp in general, is that as you slide the triangles the image will change accordingly. I start by pulling the triangles in to the edges of the image’s color levels and check the image. If it looks good, just click OK and there you go, easy color adjustment with the Levels tool.

Notice that on different images the Level Input area will be different, so just adjust the triangle sliders in from each side to the beginning of the color level for each photo/image for quick color correction: