Page #170 (136. About an Image s Histogram)

137. Improve Brightness and Contrast

Before You Begin

136 About an Images Histogram

See Also

138 Improve a Dull, Flat Photo

If you grew up using a television set that had an old style of operating control called knobs, you'll recall there were two such gadgets, generally labeled Brightness and Contrast. And if you ever played with these knobs as a childand survived with your wrists unscathedyou remember that Brightness made your picture whiter while Contrast made the blacks and whites in your picture stand out.

With all due respect to Philco-Ford, Admiral, Magnavox, and the other great manufacturers of the past century, I'm going to show you here how to use Photoshop Elements' equivalent of the Brightness and Contrast knobs. And then I'm going to rap you on the wrists if you use them too much. Actually, I'm not kidding this time: Although it does help in some circumstances to restore a more natural appearance to an image, the Brightness/Contrast command, when used too liberally, can result in a washed-out look (too bright), a washed-down look (too dark), or an underexposed look (too much contrast). More importantly, because pixels cannot have a brightness value of greater than 255 or less than 0, when you brighten or darken pixels too much, you lose the distinguishing contrasts between the brightest or darkest pixels among them. Then when you try to get those contrasts back with a Levels adjustment, you can't. With the technique demonstrated here, you can use the Brightness/Contrast command effectively and safely, without losing information in your image.


With the Brightness/Contrast command, brightness is added to an image (or to a layer or selection) by adding equal amounts to, or subtracting from, the Brightness component of every pixel in the image. So, although you might be restoring the natural brightness level of the midtones, natural darks might be washed out. By comparison, a contrast adjustment mathematically redistributes brightness across the entire image, flattening the image's histogram and reducing its peaks. However, the same danger of losing bright and dark values remains valid with contrast adjustment, except on both sides of the histogram instead of one.


Choose Enhance, Adjust Lighting, Brightness/Contrast

Open the image you want to adjust in the Editor in Standard Edit mode and save it in Photoshop (*.psd) format. To display the histogram palette if it is not already showing, select Window, Histogram. From the palette's Channel drop-down list, choose RGB. If there is more than one layer in the image, choose the layer you want to adjust in the Layers palette. If you want to limit your adjustment to a region of the image, use a selection tool to select that region. See 70 About Making Selections for an explanation.

Choose Enhance, Adjust Lighting, Brightness/Contrast from the menu bar. The Brightness/Contrast dialog box opens. Enable the Preview check box so that you can see the results of the adjustments you're making in the actual image.

In this example, the photo was taken at dusk without a flash. Although it does capture the moment, it's the worst time of day to take a digital photo for many cameras. If the flash had been turned on, the subject would have been well lit, but the sky would no longer be a dreamy blue but a dreary clay color. My goal here, for now, is to make the subject matter clearly visible while losing as little of the original color scheme as possible.


Adjust Brightness or Contrast

To add brightness value to all the pixels in the designated region, slide the Brightness slider to the right, or enter a positive value in the Brightness text box. To reduce brightness in all the pixels in the designated region, slide the Brightness slider to the left, or enter a negative value in the Brightness text box.

To add contrast between pixels in the designated region (making light pixels lighter and darks darker), slide the Contrast slider to the right, or enter a positive value in the Contrast text box. To reduce contrast between pixels in the designated region (bringing all brightness values together toward a middle gray tone), slide the Contrast slider to the left, or enter a negative value in the Contrast text box.


As you increase contrast for an image, you might notice that the black curve in the Histogram palette has "teeth" in itspecifically, evenly spaced vertical stripes. This is natural, and is an accurate depiction of the brightness values in an adjusted image. For the sake of argument, suppose that there were only 10 levels of brightness in a given image, ranging in value from 10 to 20. After the adjustment, suppose that they now ranged in value from 5 to 25. Because all pixels were adjustednone are left behindthere are still only 10 levels of brightness. They've just been broken up, such that there are pixels with brightness of 5, 7, 9, and so on, but none with 6, 8, 10, and so on. Notice in the example how the contrast-adjusted image looks spotty, noisy, and unsmooth. What your eyes see is verified by the "teeth" in the contrast-adjusted histogram.

As you make adjustments, notice the instant change to the Histogram palette. The gray curve with the bright tip represents the image's existing histogram; the black curve represents the adjusted state as you see it in the preview. With a brightness change, the entire "mountain" of the graph shifts to the left or right. With a contrast change, the entire "mountain" is flattened, as if eroded by a rising tide. While you're making these changes, watch the Histogram palette, being mindful of two things:

  • Don't adjust the image so much that pixels on either or both sides of the histogram fall off the edge. When that happens, you're losing vital information which, when saved, cannot be retrieved.

  • In the interest of restoring one of the image's qualities to a natural or pleasing appearancefor example, distinguishing a little girl from her picnic basketdon't introduce negative qualities on the opposite end of the scale, such as a washed-out tone for the grass, or water that appears to glow as if it were emanating from a nuclear facility.

To finalize your adjustments, click OK.


View the Result


If you press the Alt key on your keyboard, the Cancel button changes to read Reset. Click that button to erase your changes to the image, leaving the dialog box open so that you can try again.

In the example, after adding +30 to brightness and +20 to contrast, the range of color now looks more natural. But the image has far to go before it's fixed. In the adjustment, I did lose some of the distinguishing bright values along the right side of the histogram, although not many.

Adobe Photoshop Elements 3 in a Snap
Adobe Photoshop Elements 3 in a Snap
ISBN: 067232668X
EAN: 2147483647
Year: 2006
Pages: 263 © 2008-2017.
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