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August 31, 2007

Adjusting Levels and Curves with Photoshop

When I was working with this photo of the sunset over the Grand Canyon last night, I realized that it was a perfect photo to demonstrate the power of the two quick Photoshop adjustments that improve almost any photo. They are adjusting the levels and curves. Almost all photos benefit from an adjustment to both of these elements.

I opened the photo of the sunset which I shot using Canon's raw format (CR2). A "raw" file is actually not an image file; it's a data file that has to be opened with a program that can read it and process it as an image file. Photoshop has plug-ins for handling the raw files for all the common brands of cameras.

Here's the before and after of the image:
Before and after adjusting Photoshop levels and curvesThe original unadjusted photo has an orange cast. A lot of photos have casts, and especially wide-angle landscape photos. You can think of the cast as something like a colored mesh or filter over the entire surface of the photo. Adjusting levels will remove the color cast.

So let's start out by adjusting the levels. Create a new Levels Adjustment Layer by right clicking on the adjustment layer icon at the bottom center of the Layers palette toolbar - highlighted in yellow below: Levels adjustment layer
Photoshop will display for you at this point the Levels histogram, which is a chart that represents the color information of the image. By default you will be shown the RGB histogram, which is the combination of all the color values from zero (black) to 255 (white) for red, green, and blue combined. A good histogram will have information that runs from the outer edges of black and white for each of the color channels. We want to adjust for any gaps at the outer edges color channel by color channel.

RGB Levels channel
The RGB histogram for this photo is actually very choppy with peaks and valleys right across the range of values, and there is also very little information out to the right or the "white" end of the value range so it's probably going to be a good candidate for adjustment.

You could actually adjust the image for the RGB combination, but it's better to do it each color at a time as you will get better results. So next change the channel to Red from the channel dropdown: Red levels channel
You can see that there's a bit of a gap at the left and a larger gap at the right of the histogram. I moved the black pointer slightly in to the right, and I moved the white pointer towards the center quite a bit to a point where the histogram starts to rise.

Now I do the same thing with the green channel: Photoshop green levels channel

And the blue channel: Photoshop blue levels channel

When I have adjusted each of the three color channels, I click OK. When you do that, Photoshop extrapolates the missing color information at the ends for you and fills in the gaps. Here's how the image looks now: Image after Photoshop levels adjustment
Quite a difference already!

Now I am going to adjust the Curves. Curves are a much more subjective adjustment as you won't be adjusting to a histogram as we just did with the Levels. Rather you will move the curves and make a judgment of where the best adjustment lies.

Create a new Adjustment Layer by right clicking the adjustment layer icon again, but this time pick Curves. Photoshop Curves adjustment layer
I always start out by slightly adjusting the white and black limits of the curve. Here's how I adjust the white limit - see where I have highlighted with yellow? I nudged that to the left until the input value changed from 255 to 250. Adjusting Photoshop curves output

Then I did a similar thing with the black limit - I moved it slightly to the right until the Input Value reads 5. Adjusting Photoshop curves input
Now click in the center of the curve line and continue to hold down the mouse button. A small square or handle with appear. Move it around until you find a point where the image looks more to your liking. If the image is too dark to start with, move it up into the "white" area. By doing this you are effectively increasing the exposure. If it is too exposed, move it down into the black quadrants and make the image darker. I found for this image it looked about right at one grid down along the vertical center line. Now you will see that what was a straight line is now curved, hence the name "Curves". Picture after Photoshop curves adjustment

Click OK. This is how my image now looks. Isn't that great! Picture adjusted with Photoshop levels and curves
So by adjusting just these two simple things, Levels and Curves, you will greatly improve almost every photo you take.

1 comment:

Unknown said...

This technique is great. Works perfect!!! Thanks a million!!!

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