Histograms in Action

Recently we looked at how histograms show the tonal data of an image, now lets put them to some practical use.

Histograms are ideal to help us understand the contrast in our images. When a picture seems a bit “foggy”, we can look at the histogram and see exactly where the graph is unbalanced. Maybe the tonal information is mainly in the middle of the histogram, thereby showing a lack of both shadows and highlights; or perhaps the graph is mainly to the left of the centre showing that, while the dark tones are fine, the whites are underexposed.

Brightness/Contrast Tool

First of all I should mention that there’s a dedicated Brightness/Contrast slider in Photoshop, but I never touch the thing. This tool can be okay for quick fixes, but it’s difficult to make adjustments with any kind of precision.

The Brightness/Contrast tool basically darkens the darks and brightens the lights, making greater contrast between them. It does this broadly, with no way of adjusting the shadows or highlights separately from each other. This lack of control is frustrating to me, and this tool lies unused in my menus.

In case you do want to use the Brightness/Contrast slider, or just want to play with it and make your own decisions, you’ll find it here:

Rather than using Brightness/Contrast while adjusting the contrast in my photos, I generally use Levels. Adobe has added histograms to the Curves tool in CS4 but, while I love this change more than I can say, I’m used to the way Levels work with adjusting contrast and am happy to keep using them for this. Try following these next tutorial steps with the Curves tool as well as Levels and see what differences and similarities you find, you may find you prefer one over the other.

Contrast Adjustments – Levels

This is a very quick adjustment and is one of the first things I do when I start working on a photo.

Step One:

Open a photo that needs some contrast help.

Step Two:

Create a new Levels layer by clicking on the Adjustment Layer button at the base of the Layers palette and selecting Levels.

Step Three:

Take a look at where the main body of the histogram is, and where there are bald patches. Most of the histogram for this photo is fairly evenly distributed, but it trails off before the edges on both sides, especially on the white side.

Step Four:

This is where Levels proves its greatness vs. the Brightness/Contrast tool.

In Levels, instead of having to increase the overall contrast, affecting both shadows and highlights, you can adjust the dark and light tones separately.

To do this, you’ll be using the little adjustment arrows directly under the histogram. Slide the black arrow to the right, and the white arrow to the left, until they line up with the edges of the histogram. You’ll see the tones changing as you do this.

Step Five:

This step is optional. With some photos it makes all the difference, but for others it’s best left alone. Try it and see if you like the result.

You’ve shifted the white and black arrows, now try moving the grey one. This arrow controls the mid-tones in your photo. It tells Photoshop where the dark tones stop and the light tones begin. When I’m adjusting contrast I usually try moving the grey arrow towards the left of the histogram just a touch.

You’ll see your mid-tones start to lighten, it may look a little washed-out at first. To counteract this, I tweak the black arrow to the right a tiny bit to bring back the shadows. Play with all three arrows until the contrast is perfect.

This adjustment takes a couple seconds, and is good either as a standalone quick-fix, or as the starting point to doing more work.

Here’s my before and after:




You can see the improvement instantly.

This is how to make an overall contrast adjustment. In my next post I’ll show you how to use layer masks to make localised adjustments and bring out the best in every area of your photo.


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