Gimp 101: Levels

June 21, 2009

Well, I was planning on starting my “Photography 101″ posts next – exlpaining exposure, composition, etc. But a few people mentioned that they did download Gimp, so I’ll start with “Gimp 101″ first. We’ll move onto Photography 101 in the next post!

Today I’m going to talk about the Levels tool in Gimp, which is something I adjust in almost every single one of my photos – it’s a quick and easy tool that will make a huge difference in most of your photos. Let’s take this photo of mine that I took downtown recently:

Original Photo

I liked this picture as it was, but I thought it needed a bit more of a “pop”, so I opened it up in Gimp. The very first thing I always do in Gimp is create a Duplicate Layer. Layers are something very important and powerful in Gimp (and they’re the same as Photoshop Layers, so if you’ve used those, you know what I’m talking about). Imagine your picture is printed on a piece of paper. Then imagine that you created two of them on a piece of paper and laid one on top of the other. The top one covers up the bottom one and it looks like one piece of paper with your picture on it. Then you gave a three year-old a crayon and allowed him to go to town on the top piece of paper. What was your picture is now either a creative masterpiece or a bunch of scribbles, depending on whether or not that child was your son. The good news is, you can pick up the top piece of paper and your original image is left untouched underneath. And that’s the beauty of creating a duplicate layer. It’s not necessary, and I rarely ever go back to it, but when I do create a mess with my editing and I want to get back the original, having that original image untouched in a separate layer is really helpful. Of course, layers can be much more powerful than just keeping your original image hanging around, and we’ll get into how and why in some later entries.

To create a Duplicate Layer you can either go to the Layer Menu at the top of the screen and select Duplicate Layer:

Layer --> Duplicate Layer

…Or you can right click on the Background Layer in the Layer window and select Duplicate Layer:

Right Click --> Duplicate Layer

(on a side note, I can’t remember if that Layer window is there by default when you first install Gimp. If not, you’ll probably want to add it, it’s quite helpful. To do so, go to the Windows menu at the top of the screen and then select “Dockable Dialogs” and then select “Layers”. Voila!)

…or, if you’re into shortcuts, the other way to create a duplicate layer is to hit Shift+Ctrl+D.

However you did it, your Layers window should look like this now:

Layer Window with Two Layers

Now comes the exciting stuff. Go to the Colors menu and select Levels:

Colors --> Levels

You should now see this screen:

Levels Screen

That funky graph thing is your histogram. Here’s an article on the Digital Photography School website about what a histogram is. My short, simple definition is that it’s a bar graph showing you how many pixels of your photo are a certain tone. Essentially it means that the more stuff you have on the left, the darker the photo is, and the more stuff you have on the right, the lighter the photo is – often this means a photo is over and underexposed. So in my example, I have that big hump on the right, so a lot of my photo is light colored, which you can see mostly in the sky.

Typically you want your histogram to be relatively evenly dispersed – I hate even saying such a general rule like that, because it’s really not the case, but you should at least look at that first when you open the levels dialog. So let’s see what we can do to my photo. See those three triangles below the histogram? Those are sliders, and if I move the left-most one towards the right, that’s telling Gimp “See this point? The one you thought was dark, but not completely black? Well, it’s the new black”. So my pixels that were not completely black before now will be, and things that were dark, but not really dark, will get darker. It’s hard to explain, but easier to see, let’s slide the left-most slider (the black one), over to the right, to the first divider line:

Sliding Levels

Here’s the picture now:

After Layers Adjustment

The most noticeable difference is probably in the sky, but take a look at the windows both before and after. Until I adjusted the levels, I didn’t even realize how “washed out” the windows looked. After adjusting them, they look much more true to life – and the photo overall looks much more interesting.

So, let’s take a look at our levels now:

Levels After

It’s a bit more evenly distributed now, huh? You’ll notice, however, that there’s a sliver of a “bump” right along the left side, meaning that we have a lot more pixels and pure black than we did before the adjustment. This makes sense, though, because when I dragged the slider, I moved it past a lot of smaller humps in the histogram, so I turned all those things that before were just dark, but not pure black, into pure black. It could be argued that the histogram is even less “even” now. This is exactly why I said I didn’t like even mentioning that “evenly dispersed” rule, because I think the photo looks better like this.

Let’s try one more… here’s one of my favorite pictures:

Original Photo

It looks nice like that, but the details (like the veins on the leaf and the water droplets) aren’t really popping. Let’s take a look at the levels for this picture:

Levels (unchanged)

Notice how there’s (essentially) no pure black or pure white in this photo, so I fixed that by moving the black slider to the right and the white slider to the left:

First Levels Adjustment

It’s looking a little better now – the colors definitely pop more – but I’m still missing that detail I want:

First Layers adjustment

So now it’s time to mess with the middle slider – the midtone one. This is basically pure gray. It was a lot harder for me to grasp what to do with this slider than it was to figure out the left and right one, but here’s how I think of it: If I move the middle slider to the left, there will be a greater amount of pixels between the middle slider and the white slider, so more of the picture will be lighter. If I move the slider to the right, there will be a greater distance between the black slider and the middle slider, so more of the picture will be dark. And this is what I want to do. I want to make those midtones darker in order to bring out the detail of the leaf and droplets, so I move it right about here:

Adjusting Midtones

BTW, there was no science to wear I moved this, I just moved it until I thought it looked good in the photo, which now looks like this:

Final Picture

So there you have two examples of playing with levels. Try it out on your own photos!

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  • skydvr

    Very easy to understand examples. Thanks much! DPS led me here, and I really like your site so far.... I look forward to exploring it more...

  • Does gimp have a preview of the clipping in levels? This page explains it:

    http://www.zuberphotographi...

    It is literally the only thing I have in photoshop that I don't see in other programs. It lets you adjust the slider and get a visual indicator of what parts of the image are going to become pure black or pure white. This is useful for portraits because you can adjust the black and white levels until you see clipping on the person which ends up making the image "pop" a little.

  • Unfortunately, as far as I know, this can't be done in Gimp

  • emma

    wow, its so easy! never realised what to do with them earlier...

  • kvanbuskirk

    Thank you SO MUCH for giving a tutorial on this that I can actually understand! All of your entries are so helpful...keep it up! Pretty please?

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