levels – In Photos dot Org

GIMP For Photographers: Levels

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.

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?

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.

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

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.

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:

The Levels tool on gimp.org docs
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.

Simple steps to photo touch-up

In this post I’m going to show you how to go post-process this image:

By the end, we’ll have an image that looks like this:

This tutorial was created using the GIMP, but it’s equally applicable to your favourite editing software as long as it has the same tools. Photoshop, and other editing software should work equally well.
The steps described here are worth practising, and will apply equally well to any portrait!

First of all, I came across this photo on Flickr through my contacts page. Here’s the original photo, and Ayhtnic kindly let me use her image.

After you load the image, the first thing to do is use Auto Levels from the Layer->Colors menu. This tool alone does wonders for most photos, especially if they’ve been captured as Jpeg straight from the camera.

The image is a little noisy so let’s clean it up a bit. Use Selective Gaussian Blur from the Filters->Blur menu. Use small values as we just want to smudge the noise away without losing too much detail. A radius of 3, and delta of 10 worked fairly well here.

Let’s brighten it a bit and add contrast. Use the Curves tool from Layers->Colors for this. The classic “S” shape always adds life to a photo.

Open the Layers dialog and duplicate the background layer.

Select the new layer (called “background copy” here) and use the Curves tool again to brighten this layer a lot.

With the same layer selected (the top one, the “background copy”), we’ll apply some blur. Open up the Gaussian Blur tool, it’s in Filters->Blur. Apply a blur of 5 pixels to the top layer. Don’t worry, we’re not finished!

We’re going to change the “mode” of the top layer now. With the top layer selected, click on the dropdown box that says “Normal” and scroll down to “Soft Light”. You can also try other modes, they’ll make for interesting photos!
Notice how the image suddenly changed?

Even with the nice glowing effect, the image looks indistinct. Let’s sharpen the bottom layer. Select that layer in the Layers dialogue and load the “Unsharp Mask” filter. This is in Filters->Enhance->Unsharp Mask.
Don’t apply too much sharpening. Make it subtle. The settings in the screenshot work well.

All that’s left is to save the image, save it with a quality setting of 92%. Don’t bother with higher, as it’s practically impossible to see any difference in quality.