How To Use the Levels Tool in GIMP {Complete Guide}

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The Levels tool is like a Swiss Army knife… it has multiple tools built-in. Levels have three main functions; adjust the exposure, tones, and color balance. The great thing about Levels is, it makes some other tools in GIMP redundant.

Using Levels can speed up your workflow since you don’t have to jump around to different tools. Oh, and it’s nice to preview all those edits in one place to see how they complement each other!

Table of Contents

Levels Tool Deep Dive

levels

Let’s explore the Levels window in-depth, to discover its extraordinary magical editing powers! To pull up the Levels window, go to the menu under Colors > Levels. To expand the window, click a side or corner and drag it out to make it larger.

Channel

Next to “Channel,” you’ll find a drop-down menu labeled “Value.” From here, you can select one of the three RGB channels (red, green, or blue) to target for editing. If you find your image has a red color cast, you can adjust the Red channel to remove it!

Input Levels

The Input Levels displays the histogram of your photo and will update according to the channel you select. By default, it’s showing the luminosity (brightness) of your tonal range… or the dark, middle, and light pixel values of your image.

As mentioned in this tutorial, the histogram comprises five segments consisting of your images tonal range. This includes the Black point (pure black), Shadows, Midtones, Highlights, and the White point (pure white).

Adjustments can be made to set the Black + White Point, increase or decrease the exposure, color balance a specific channel, and adjust contrast. That’s a lot of editing options built into one tool!

Just below the histogram, you’ll find a bar with three marks, one on each end and another in the middle. These markers are used for adjusting the Black + White points, contrast, and exposure.

Below the bar, you’ll see an eyedropper tool on each end. One is for the Black point, and the other is for the White point. To use the eyedropper tool, click on either icon to activate it. Then, you can set the tone point by clicking on your image.

The numbers next to each eyedropper tool represent the far ends of the tonal range. Zero is for the Black point, and 255 is the White point.

Output Levels

The Output Levels bar will allow you to change your Black point to a lighter gray and the White point to a darker gray. 99.9% of the time, you’ll never use this! One application would be used for creative adjustments. Another would be if your in-home printer, for example, can’t output pure black. Or maybe you want to conserve the black ink!

All Channels

The Auto Input Levels button gives creative control over to GIMP, and it will “auto” adjust your Levels settings. To the right, you’ll find three eyedropper tools. With them, you can set the Black, Gray, + White points automatically when clicked.

Edit These Settings as Curves

The Curves tool provides more precision and control vs. the Levels tool. If you’d like to switch your current settings to work with the Curves tool instead, click this button. GIMP will then open the Curves tool with your settings accordingly.

Blending Options

Blending Options allow you to choose a layer Mode to be applied with your settings. Expanding this section will reveal an Opacity slider.

How To Fix An Overexposed Image With Levels

over exposed image sooc

This image is slightly overexposed and can be fixed with the Levels tool.

I shot this image on a bright sunny day, and the photo turned out to be a bit overexposed. It’s an easy fix with Levels.

fixed with levels

First, review the histogram in the image above and notice the shape. It’s showing detail in the majority of the tonal range. There’s a small gap on the left (Black point) that needs to be filled. Overall the exposure isn’t that bad.

The first step for editing this image would be adjusting the Black point. Notice how I moved the left marker to the right and aligned it to the histogram’s edge. Any further to the right and detail would have started to be clipped.

The middle marker was also moved to the right. This time, there isn’t an edge to align to. Instead, I adjusted what I thought looked good… on my monitor.

I trust that when I send this to a pro lab for printing, it will come back correctly exposed. This is due to having calibrated my monitor and having test prints done with my favorite lab.

How To Fix An Underexposed Image With Levels

under exposed image

This image is underexposed and the dark areas (hair, clothes) are blending in with the background.

Fixing an underexposed image isn’t that much different from the last edit. Again, let’s review the next picture and its histogram first.

fixing the under exposed photo

It’s hard to see in this image, but his hair is no longer blending in with the background.

Notice how the prominent peak is concentrated on the left side. This is an excellent indication that the image is underexposed. There’s also a small gap on the left and a slightly larger one on the right side.

The question is, should the gaps be filled? Yes and no! I don’t mind adjusting the White point to fill the void. Which you can see was done with the right marker… again along the edge of the histogram.

The other gap is teeny tiny. Filling it would close the gap, but it would also make the image darker! Take a close look at his hair in the original. You can see it’s blending in with the interior of the building. If I were to adjust the Black point, it would make this happen again. So, I decided to leave the gap this time.

This time, for the middle marker, the adjustments were to the left to increase the exposure. On another note, a vignette was added to this image, which you can learn to do here.

Pro Tip:

There’s one problem with the edit of the underexposed image above… it’s now overexposed! How do I know? GIMP told me so. To ensure you’re not over editing, it’s a good idea to have the “Pointer” panel visible while editing. Go to Windows > Dockable Dialogs > Pointer to reveal the panel.

When you hover over your image with any tool (I prefer the Move tool), the Pointer panel will reveal data about the picture’s pixels. The data you want to be mindful of is the RGB info. Personally, I prefer the percentage data since the overedits stand out like a sore thumb.

checking over under exposure with pointer panel

For this edit, the young lady’s skin was sampled, and you can see the percentages for each channel as follows…

If you look at the RGB data to the left, you can see red is at 255. 255 equals pure white or 100%. Pure white means no data… or no detail! The edit of the White point overexposed her skin… which isn’t a good thing. The solution is to move the white marker back to the right until the red channel drops below 100%.

How To Color Correct An Image With Levels

green tint

A green color cast is present in the original image and was fixed with the Levels tool.

The Pointer panel shows that there’s a green tint.  Click to enlarge.

Pointer panel shows the RGB channels are now equal.

Our next image has a green tint. It might be hard to see it, but it’s there. If you’re having a hard time seeing color casts use the Pointer panel to tell you which color is dominant. Let’s review the data that was sampled from his shirt…

The green channel is clearly dominant! To remove a color cast, you want all three channels similar to each other in percentages.

To fix the green tint, go to the Channel value drop-down menu and choose “Green.” Adjust the middle marker to the right to add Red. Then, use the Pointer panel to ensure the RGB channels are closer to equal.

After the edit, you can see that the channels are now all in the 82% range (see second image in left column). The color cast has now been removed!

What's Next?

The Levels tool provides multiple editing options in one and can streamline your workflow. But you know what’s even more powerful? The Curves tool! 

It, too, has the same editing options but provides a magical element, not even the Levels tool has. Find out more about the Curves tool here.

Like this article? If so, please share!

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Hello! My name is Chris Parker and I run this place. But, more importantly, what’s in it for you? Well, my passion is to help you achieve your creative vision.

With 30 years experience I believe I can help you do just that. So, if you’re ready… let’s do it!

 

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