Page #171 (137. Improve Brightness and Contrast)

138. Improve a Dull, Flat Photo

Before You Begin

136 About an Images Histogram

See Also

127 Restore Color and Tone to an Old Photograph

137 Improve Brightness and Contrast

144 Correct Color Manually

Perhaps the real revolution in computing has finally been realized with the introduction of color photocopying systems into the average home. Today, the everyday individual has it within her grasp to duplicate photographs and documents with astounding resolution and brilliance. But xerography is by no means a perfect science. In the act of copying a color photograph, so many translations of color tables and formulas take place that the initial product often ends up washed out, as if it had been left out in the sun for several weeks.

In this task, we'll restore some of a faded, scanned photograph's natural brilliance and contrast by narrowing the range of its input levels. A similar feat of restoration is demonstrated in 127 Restore Color and Tone to an Old Photograph, although the parts of the Levels dialog box we'll use here focus primarily on regulating the three primary color channels. When a photograph fadesas the one in this example didnot only does it take on a decided color cast, it loses its darkest darks. With the Levels command, this task demonstrates bringing those natural darks back, one channel at a time, paying attention to the histogram all the while, and relying on what you know about what color things should be to help you out.


The scanner drivers shipped with many flatbed scanners tend to use their own automatic levels correction when scanning faded photos, especially black-and-whites. More often than not, these drivers tend to overestimate their own corrections and perform too much contrast adjustment. Rather than wrestle with undoing in the Editor the errors that your scanner driver caused, try turning off the automatic correction feature before you proceed with the scan, and then make the right corrections yourself with the Levels command. See 6 Import a Scanned Image for more about bringing an image into the Editor or the Organizer from a scanner.


Choose Enhance, Adjust Lighting, Levels

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 Channel drop-down list, choose Colors. If there is more than one layer in the image, choose the layer you want to adjust from 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.

From the menu bar, select Enhance, Adjust Lighting, Levels. The Levels dialog box opens to display a histogram of the picture. Enable the Preview check box so that you can see the result of the adjustments you make in the actual image.


Choose a Channel

From the Channel drop-down list, choose whether you want to adjust the RGB channel (the combined brightness of all three color channels) or the color value of the Red, Green, or Blue channel independently. For a grayscale image (especially a grayscale TIFF), this setting will read Gray and will have been made for you.


Adjust the Input Levels

The histogram shown in the Levels dialog box represents a brightness scale, showing all possible brightness values in the image for the chosen channel, for all possible values between 0 and 255. A clear indication that an image can be lightened is when few or no pixels are registered in the rightmost region of the histogram.

The white point of an image represents the pixel or region of pixels that should be the brightest region, and therefore perhaps should be corrected to become pure white. The Levels dialog box begins by representing the theoretical white point as the white up-pointing arrow on the scale just below the histogram, on the far right side. To try brightening the image, slide the white point to the left, toward the right tail end of the charted pixels in the histogram. The white point on the histogram is like one side of a fence. Wherever you set it, all pixels represented on the histogram that are currently plotted at the white point or higher, will be altered to the maximum brightness level represented in the second box above the graph marked Output Levels. Then all the other pixels' brightness values from that point toward the left side are rescaled upward, rendering them brighter in the process. The Histogram palette shows the effects of this change the moment your preview of the image changes. No distinctions or contrasts between pixels are lost unless pixels on the histogram fall to the right of the white point.


Black and white points Pixels in a photo that should be pure white or pure black. By identifying these pixels, you can correct the color balance and tone throughout an image.

The black point on the histogram is on the other side of the scale. When the Levels dialog box first appears, the black point (the black up-pointing arrow on the scale just below the histogram, on the far left side) is set at 0. To darken the image, slide the black pointer to the right. Wherever you set it, all pixels represented on the histogram that are currently plotted at the black point or lower will be altered to the minimum brightness level represented in the first box above the graph marked Output Levels. Then all the other pixels' brightness from that point toward the right side will be rescaled downward, rendering them darker in the process. No contrasts will be lost unless pixels on the histogram fall to the left of the black point.


Adjusting the gamma will give you weird results if you don't adjust the white and black points first. The gamma describes an important geometric point on a curve. The white and black points are at opposite ends of this curve. Adjusting the gamma is almost pointless if you intend to adjust the white and black points later, which will move the curve.

By moving the white and black points, you're "fencing in" your photograph, ensuring that there is a black and a white somewhere. For most images, this is what you want.


Suppose that you are preparing an image for printing on a commercial press. You've been told that the press cannot reproduce detail in highlights where the amount of ink required is thinner than 5% of the maximum. You can use the white Output Levels slider to set the brightest point to 242which, when rounded off, is 5% less than the maximum of 255. This setting ensures that the press will reproduce all your highlight detail. You can make a similar adjustment to allow for press characteristics in printing shadow detail.

You can use the eyedroppers in the Levels dialog box to select black, white, and neutral gray points. Click the black eyedropper in the dialog box and then click a point in the image to identify that point as the blackest. Click the white eyedropper and then click in the image to identify that point as the whitest point in the image. The adjustment that Levels makes creates a new brightness curve between the two points you select. For more about using eyedroppers to set black, gray, and white points, see 127 Restore Color and Tone to an Old Photograph.


Adjust the Gamma If Necessary

The gray pointer in the middle of the scale represents the degree of bias in determining how to rescale the brightness values of pixels between the black and white pointers. As you move the black or white pointer, notice that the gray pointer also moves, registering the same gamma bias applied to the relocated scale. A gamma of 1.0 implies no bias toward either brights or darks. To make more room for bright pixelsbrightening the overall image and increasing the gammaslide the gray pointer to the left, toward the dark side. This reduces the interval between the black and gray pointers, indicating less room for darks and more for brights. To make room for dark pixelsdarkening the image and decreasing the gammaslide the gray pointer to the right.

For this example, noting how red this photo had become, I started off by making adjustments to the Blue channel. I moved its black point to 44, at the left cusp of the curve. I then tried several gamma settings before settling on a startlingly high 2.22 (up from the presumed normal setting of 1.00). In judging whether these settings were right, I kept an eye on the Histogram palette, which shows the increased spread in brightness in comparison to the other two channels. I also took note of my wife's collar. (Yes, that's my wife, circa 1975. No, that's my brother-in-law.) I knew she was supposed to be wearing a white pullover jacket with patriotic blue and red trim. What I tried to do was bring back as much blue as possible without making the pine tree behind them look like a blue spruce.


View the Result

When you're satisfied with the result, make any other changes you want and save the PSD file. Then resave the result in JPEG or TIFF format, leaving your PSD image with its layers intact so that you can return at a later time to make new adjustments.

For this example, after restoring the Blue channel, I proceeded to the Red channel, raising its black point to 92 and its gamma to 1.50. For the Green channel, I raised its black point to 46 and its gamma to 1.91. Those numbers, in and of themselves, probably seem pointless on the surface; but take a look at the Histogram palette for the result figure. The three color channels now begin and end at basically the same point on the graph, and their peaks and valleys are more in sync with one another. The numbers I just rattled at you were the ones that put this histogram in sync. Now the pine tree is green, the blue jeans are blue, the silver garland isn't wine-colored, Mike's hair is…there, and my wife is a striking brunette.

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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