Adjustment Sub Menu: Contrast Controls

Controlling the color of an image is the ability to change the contrast. This is used either to correct the tonality or to increase or decr...

Controlling the color of an image is the ability to change the contrast. This is used either to correct the tonality or to increase or decrease contrast for effect. Other adjustment in colors,

• Contrast. Aside from color, the ability to change photograph's contrast is one of the most important controls of this program. Photoshop offers several different methods.
• Levels. By far the most useful contrast and tonal control is Levels. Use it for changing the contrast and tonality of shadows, mid-tones, and highlights, not only on a four color photograph, but also to each of the re, green, and blue channels. This, in turn, can also control color balance.
• Adjusting contrast. Beneath the histogram are three sliders, representing shadows, mid-tones, and highlights. When adjusted separately, they will change the brightness of that part of the tonal range. Moved to the left, it becomes brighter between the three parts of the tonal range determines the contrast of the image. Though each image will require individual correction, it is a good idea to adjust the shadows and highlights first, to set the darkest and lightest part, and then adjust the mid-tones.
• Histogram. The histogram is a diagram of the level of tones a photograph contains-running from left to right:shadows, mid-tones, and highlights. A low-key image with a large amount of shadow tones would show a high amount of activity on the left of the histogram. A high-key image, which would be very light , would show more activity on the right. Ideally, a photograph should have an even range of tones and show a smooth progression from left to right.
• Clipping. The histogram should ideally have information throughout the whole of the graph, even if in parts it is just a thin line, as this means that there are at least some pixels present in every part of the image. If either end of the histogram is just empty space, known as clipping, then it is advisable to move either the left or right slider until it just touches the start or end of the histogram.
• Spikes. Though a smooth histogram is desirable, often, long spikes will appear showing that there is some interference to the total range. This occurs particularly when the image has been heavily manipulated. It is sometimes possible to smooth this out by reducing the image size slightly before any manipulation. open the Image Size palette and reduce the length by 5 pixels to the length. Comparing the histogram before and after this final step should show a reduction in interference.
• Color controls with levels. Separate colors can be adjusted with levels by choosing red, Green, or Blue from the drop-down channel menu. Move the slider to the left to decrease the relevant tone while adding the chosen color. Move the slider to the right to lighten the tone but add the opposite color. This can be very effective in reducing a color cast or introducing a color such as yellow (the opposite of blue) to create a warm summer feel.
• Tonality. Beneath the histogram is a tonal scale, again running from left to right, that can be used to alter the overall density of the shadows and highlights. When the right hand slider is move to left, the highlights increase in density. When the left hand slider move to the right, the shadows decrease. By the time the two meet in the middle, the whole image will have turned gray. Use this control sparingly and in conjunction with the finer tonal controls described previously.
• Curves. As an alternative to levels, many photographers prefer to use Curves. it is based on the "characteristics curve" in the film photography to diagrammatically show the contrast of a processed negative. Bottom left represents the shadows, top right the highlights. In between, a straight line shows mid-tones, the more "contrast" the photograph. In Photoshop, points of the curve can be dragged to after sections of the tonal range.
• Shadow/Highlight exposure. Instead of using it to alter overall contrast, use shadow/highlight to improve the tonality at both ends of the contrast range. Lighten Shadows can bring a bit more detail into dark areas, but should be used sparingly. Darken Highlights is far more effective. If used carefully it will tone down highlights so they do not glare so much. However, no difference will be made to pure white tones.
• Avoid halos! Extreme changes to contrast are best avoided with the Shadow/Highlight command as they are prone to giving coarse results and sometimes a halo or soft line will appear between different tones.
• Brightness/Contrast. To decrease the level of brightness or contrast, drag each slider to the left. To increase the levels, drag to the right. However, other controls, such as levels, allow far finer contrast and tonal control. Brightness/Contrast does have its users when changing a selection (a part of an image), especially when there is only one flat tone involved. It is then best used as an Adjustment Layer.