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Tuesday, July 28, 2009

Photoshop Quick Tips #2 – Curves

(Download link is at the end of the tutorial. Please note that the files are now password protected, and the password is also at the end of the tutorial.)
image showing the curveslayer in photoshopCurves allows you make adjustments to colour and contrast with a little more control than any auto function, and even a little more than the levels tool. Open up your "Brown Dog" photo and we'll play with this a bit. Although the colour and contrast isn't too bad, this will allow you to see what the curves function can do.

The first thing to do is duplicate your background (right click on the background layer in the layers palette, select duplicate layer) and name it "Curves Layer". Now open the curves tool - you'll find it in the menu under Image > Adjustments > Curves. You'll see a square divided into equal sections with a line from the bottom right corner to the top left, and a graph-like image in gray tones. This graph is the histogram - it represents light, dark and medium toned pixels in the image.
image showing the dialogue for curves box in photoshop
In the preset box at the top there should already be some settings. You can click on those. When you open the box it probably says "none". Click the little drop-down arrow and select a preset. Watch what it does to the image, and to the curves line.
image showing the result of the negative function in photoshopLet's try the preset "lighter". And then look at the preset for "Negative".

hmmm. This isn't really what we want. Click the "none" in the drop down box to return to the original image. There is another button to the left called "options". Click that and play with the choices a little. This box allows you to select "auto" color correction options. Click the different radio buttons to see what they do. Okay, close the
box without making any changes (cancel). If you click the auto button, you'll get a similar result to whatever was set in the options, but lets not do an auto right now.

Below the graph are three "eye droppers". These represent the white, gray and black in the image. What you click on using these eye droppers can have a huge effect on your picture in terms of colour correctness and white balance. Select the eye dropper on the right - that one is for white. To use this, click on the whitest part of your photo - in this case it is probably the bit of tooth to left of the dog's tongue.

image showing the white dropper in the curves function in photoshop
Now select the dropper in the middle. That's for grays. You should select a part of your image that seems to be as neutral a gray as you can find. Let's try the dog collar with this one. That gives the image a different colour cast. If you pick something else now, like the grayish-blue line along the background, you'll get something different. (don't do it right now).

image showing the gray dropper in the curves function in photoshop
You'll notice changes in the curve line over the histogram with each selection you make. Now try the black one. Click on a really black part of the image, like the front part of the dog's nose.

image showing the black dropper in the curves function in photoshop
If you look over in the layer palette and look closely at the background and the curves layer, you'll what look like some slight changes in colour and brights/contrast. Okay, for the moment, we'll accept these changes. Click "okay" in the curves box to make the changes to the curves layer. Now, click on the little eye beside the curves layer in the palette - that will make your layer "invisible". This is where you see the difference between the beginning image and the changes we made with curves. Turn the curves layer on and off a few times by clicking the little eye to see the differences.

image showing the curves layer on
image showing the curves layer off

To my eye, this "auto-ish" type of colour correction doesn't always give you the result you want, and highlights in the dog's fur look to have a pinkish cast to me. If you open the curves box again, You'll likely notice some crenellations in the histogram - these represent the changes we made. We can reduce the red a little in the fur by selecting the "red" channel instead of the RGB channel. Notice the histogram in the background changes to red?

image showing the red channel in curves
In the upper right hand corner, grab the "line" and pull it slightly downwards and watch as the pink tones change slightly. The output reads at 246 on my sample. That's still not quite enough, and I don't like the pink that's still there. Let's change the figure in the output box to 240. Click in the box and type in 240. Now click okay in the curves box to accept the change. Being able to type in a value
gives you even more control than dragging the line. If you like the image the way it is, you can flatten and save it. But let's try a couple of other adjustments.

Open the curves box again. I'd still like to lighten the mid-tones a little in this. One way is to put your cursor in the middle of the box, right in the center when the curves line crosses over the group of squares. First lift gently upwards, just a little...now move to the right, just a little. In the sample, the input box reads 138 and the output box reads 147. Another way is to add a couple of "points" along the curve line to make even more controlled changes. That's a little more in depth than what we want to do in this Quick-Tip tutorial. For now, lets accept the current values by clicking okay.
image showing the BrownDog adjusted having used the curves functionNow you can flatten your image and save it with the name
"Brown_Dog_Curves.jpg".


Practice playing with the curves tool on your own. And remember - you learn by doing. Don't be afraid to explore the tool further. Try it on some of your own images. You might be surprised at the results.

Feel free to send me your before and after images of your own work and I'll whip up a page of comparison's to show people! (small size please)

DOWNLOAD THE FULL TUTORIAL WITH ADDITIONAL PICTURES TO HELP YOU FOLLOW THE STEPS – CLICK HERE

PLEASE NOTE! – THE PDF IS PASSWORD PROTECTED. The Password to open the file is notheft

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