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GIMP For Photographers: Levels

GIMP Colors Many people find using the GIMP or Photoshop a daunting prospect but in fact those packages are quite easy to use once you’ve practiced a few times. This will be the first in an occasional series to help photographers use the GIMP to post process their photos.

The Levels tool (right click on your image, select Colors, then Levels) is used to adjust the levels of the colours in your image by manipulating a histogram representing the image. In simple terms, you can make broad changes to the Red, Green, Blue and overall “Value” parts of your image.

The single most useful function of the Levels tool is the “Auto” button. Click that button and the histogram will be stretched out. Your image should look better. If the photo lacked contrast, it can suddenly become a lot “punchier”!

Here’s an example which will make things clearer.

GIMP Levels before example

This is a nice photo I took in Galway in 2005 with a Sony 717. Unfortunately, there’s a nasty yellowish sheen to the image. I probably shot this with the white balance set to cloudy. That can give a pleasing golden look to images but it’s not always welcome. The image also lacks contrast and looks under exposed. How do I fix that?

GIMP Levels

Fire up the GIMP Levels tool. Right click on the image, go to Colors, then Levels. This is the histogram for the image above. See how it’s all bunched into the middle? Now, click on the “Auto” button.

GIMP Levels after example

Wow! One click did that? The image looks so much better now! The swans actually look white and it’s brighter and shiny!

GIMP Levels

I opened the Levels tool again, just to see what effect “Auto” had on the histogram. Sure enough. It’s stretched from side to side.

Levels before and after
Before and After Auto Levels

Wasn’t that easy?

Advanced Usage
You may have noticed the eyedropper buttons next to to the Auto button. Those are “Black”, “Grey” and “White” selectors. Click on one of those, your cursor will change to a eyedropper and then click on the corresponding colour in your image. They work pretty well, but can be confused. If it all goes wrong, just click the Reset button, or CTRL-z to undo if you’ve clicked OK.

You can also manipulate the histogram manually. Just drag the sliders left and right until your image looks ok. You can change the channel with the drop down at the top of the Levels dialog. Changing individual channels does interesting “cross processing” things to an image.

External links:

  1. The Levels tool on docs
  2. Levels Tool – white, black and grey to the rescue! – a tutorial I wrote about the levels tool back in 2004!

Want to know more? Leave a comment. I’d love to hear what you’d like to know and learn about the GIMP.

By Donncha

Donncha Ó Caoimh is a software developer at Automattic and WordPress plugin developer. He posts photos at In Photos and can also be found on Twitter.

13 replies on “GIMP For Photographers: Levels”

Oh Man, youre giving away the tricks of the trade! 🙂 I said I was going to give GIMP a go ages back but I still havent. The last time I used it was years ago on Linux and it was kinda crap, it seems to have come on leaps and bounds now though. It will be very hard for me to break away from PSP because I’ve been using it for so long but free is free I guess. Right I’m downloading it.

Oh btw, which do you find yourself using more, levels or curves?

Hehe. Post processing is only half the battle. You have to take the photo first! Glad you’re going to give it a go again.

I use levels and curves for different tasks so it’s hard to say what I use more. I also shoot in RAW now and process the RAW files through Bibble Labs first which does it’s own auto levelling.

Curves will be the subject of my next tutorial! 🙂

Fantastic, you’re definitely helping some folks learn with this one. Those gaps in the histogram after you ran the test on “auto”…the worst, nobody wants gaps in their spectrum Thanks for sharing!

Thanks for the levels tute. I have been using GIMP for about 12 months now and i’m learning more all the time.

I would love to know what techniques you use to get your B&W photos looking so good. I’m sure there is more to it that just desaturating or changing the colour mode to grey. If you have the time and can manage a short tutorial that doens’t give away all of your trade secrets I would really appreciate it.

May I suggest a way to improve your tutorial?

You just explained how to click on “Auto”. Then, when it comes the real stuff, you just wrote:

“You can also manipulate the histogram manually. Just drag the sliders left and right until your image looks ok.”

Perhaps, it would be nice to know what does it mean to move those sliders for the image.

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