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.

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Histograms Demystified

Histograms are a much misunderstood species, but can be an incredibly useful tool for any photographer and Photoshop artist. In my previous tutorial about clearing a colour cast I have already shown one example of how you can use these graphs; there are countless other ways they make themselves invaluable. And it’s not just in Photoshop that histograms are a useful guide. They can also be found in the display options of all digital SLR cameras, and most point-and-shoot cameras, and can be a useful aid in achieving correctly exposed photos.

I use them constantly while I’m working in Photoshop, so before I write any more tutorials that use these I’d like to give a quick explanation as to what it is you’re looking at, and why they’re so helpful.

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Straightening using the Ruler Tool

Today’s tip is one that has saved me at least a couple minutes on every photo I’ve used it on… if I multiply all these minutes by the amount of photos I’ve edited, it equals a rather large amount of time saved.

When you’re shooting without a tripod, or on a boat as I was when I took the example photo, there will almost always be a slight angle to some of your horizons. I find that often when I have a niggling feeling of something being wrong with one of my photos, if I check the horizon I discover that it’s slightly tilted. Sometimes only by a degree or so, not enough that it’s obvious, but enough for me to feel that something’s not right.

To fix this problem you can either carefully rotate the photo to the right and left a degree here and there, until it starts to look straight. Or. You can use this very useful little tool to fix it in seconds.

Step One: Take a photo that needs straightening. In this example the waterline is only off kilter by a tiny amount, but it’s enough to make a difference.

Image in photoshop, crooked waterline

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Clearing a Colour Cast

This is a tutorial for one of the Photoshop techniques I use the most. It’s a great help in quick photo clean-ups.

So, let’s say you have a photo and the colours just aren’t quite right. Maybe there’s a bit of a haze, or there’s a slight colourcast over the image. Try this 30 second adjustment and see what happens.

As an example I will use a photo I took while flying over the Alps this summer. In my experience photos from the air, or across long distances, never look quite as striking and clear as the view when we took them. The moisture in the atmosphere clouds things a little. Before learning this little trick, I used to spend ages with masks, levels and selective colouring, trying to get my airplane photos looking like they should.

Try this:

Step One: Open a photo that needs some work (feel free to save my “before” image from the bottom of this tutorial and practice on that). Hazy and brown, not so nice. This is my CS4 workspace.

Step Two: Create a curves adjustment layer by clicking on the adjustment layer button at the bottom of the layers palette.

(Note: If you’re using CS2 or earlier, your curves palette won’t have the histogram that it does in CS3 or CS4. To do this tutorial and get the same result, open a Levels Layer here instead.)
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