GIMP for photographers: use levels to improve your images!

In a series of blog post I will introduce you to the open-source software solution known as The Gimp! This series focuses on the Gimp features that are specifically related to photography. This post is an introduction to general adjustments using the Levels panel in The Gimp.

The image I use for this post, (almost) straight out of camera, can be downloaded here. It is nice to follow along in the start. If you feel like it go ahead and use your own images right away!

What will you show me in this tutorial?

In its simplest form: How I got from the image on the left to the image on the right in a few easy steps.

Can you see the difference? I bet you can! The image on the right is warmer, and the colors make you feel like it is a lovely summer day. Just as it was when I was out shooting. Actually, this was a bad shot. My white balance failed.

Read along and let us see how I corrected white balance and enhanced contrast. After reading this, you’ll have a fair idea how to try it on your own images.

Get started:

Open the image you want to adjust and your GIMP should look kinda like this (depending on your individual layout of the GIMP interface).

I think the image is to blue and cold, I miss the sense of the warm summerday where I went to the woods collecting mushrooms with my family.

Levels to the rescue!

To open the ‘Levels’ dialogue. Go to Colors –> Levels. Like this:

This should open up a dialogue looking like this:

Breaking it down: what’s in the ‘Levels’ dialogue box?

First you have the ‘Presets’ drop-down menu. It’s probably empty right now, but by clicking the blue + icon, you can easily add your own presets to the image.


Here you can choose which of the color channels (Red, Green or Blue) you want. By default it’s set to ‘Value’, letting you affect the whole picture.

If you choose a specific color channel, you’ll be adding or removing that color. Remember though, if you remove a color you will increase the amount of its complementary color.

(Red = Cyan, Green = Magenta, Blue = Yellow) (RGB = CMY)

Input Levels:

The main part of this area is the Histogram. The Histogram is a graphic representation of dark, midtones and highligts in the active layer.

So, how do you read the Histogram? Read it all <– insert link –>. It will help you to understand your pictures a lot better.

The sliders allow you to decide if more of the photo should be total black or peaked white.

The eyedropper tools:

The eyedropper tools in the bottom right corner allows you to correct the white balance of the image. You simply choose one of the eyedroppers (100% black, 18% gray or 100% white), and then click on a part of the picture you know is 100% black, 18% gray or 100% white. The Gimp will then correct the color channels automatically. You could also try your luck by pressing the Auto button next to the eyedropper tools. It’s the same feature as choosing Colors –> Auto –> White Balance.

Edit these Settings as Curves:

Simply opens up the ‘Curves’ dialogue, allowing you to edit the same stuff in a curves diagram. Which is nice if you want to add a quick S-curve for more contrast in your photo, I’ll get back to that later. Don’t worry.

What can I use all this for?

Now that you know the basics of the ‘Levels’ dialogue – and a bit more – you’re ready to make the dull, and boring image of mushrooms sparkle!

Here’s what I did, and why I did it – of course.

First, I wanted to get a warmer feeling in the image. To get a bit closer I’ve selected the ‘White’ eyedropper tool and tried clicking around in the sky – there is a little peak through the leafs in the upper left corner. I’ve marked the part in which I clicked to achieve this result.

Remember, you can always just click around in the white area until you get the desired result, or something close to it.

By clicking a white area with the ‘White’ eyedropper tool I’ve told The Gimp what is to be considered white in my photo.

Next I’d like a little more contrast in the image. So I added a little change to the ‘Input Levels’ on the ‘Value’ channel.

Resulting in this:

Okay. Getting closer. Now I’d like to get the moss a little more green.

By choosing the ‘Green’ channel I can increase the green in the picture with the furthest right slider. This can also be done with the other channels, of course. Here you can manually increase or decrease amounts of certain colors.

This little adjustment should result in this:

To enhance the brown colors of the mushrooms and the roots above I want to increase the red colors in the image.

I gave the ‘Red’ channel a little boost.

Resulting in this:

The last little change was to the ‘Blue’ channel.

Here I decreased the blue in order to get an even warmer more yellowish image.

Adjusting colors and setting the white balance can be a strong creative tool. You can really create a feeling, and like in my example you can even do it with a photo that would otherwise fail!

Remember, photo editing in The Gimp, and other software, is damaging the image quality a bit. You should always try getting as close as possible to the feeling you want when you have the camera in your hands. Sometimes it is just fun and super nice being able to save an otherwise dull image. And in The Gimp it’s all free