When editing scanned or digital camera pictures, other programs can hardly top off Photoshop's excellent tools and features. Under Image > Adjust, you can manipulate the picture's hue and saturation, levels, contrast, curves, and color balance. These tools enable the user to enhance any picture. For the basic purposes of this site, we'll go over the main features when adjusting images.
When you open the Levels dialog, you are presented with a histogram that represents the pixels of your image in graph form. As shown from the gradient at the bottom, the number of pixels the image contains is charted from dark to bright tones in a left-to-right manner. The levels from which this picture was taken is from Photoshop's Waterfall(16bit).tif, which is included in the program's sample files directory. In this example, there are very few white pixels, as shown on the right-hand side of the histogram.
Open the example by going to File > Open, and find Waterfall(16bit).tif in Photoshop's samples directory. Once the image is opened, go to Image > Adjust > Levels, or use <Ctrl>L (Windows) or <Cmd>L (Mac OS). Sure, this is a nice waterfall with dark green foliage all around, but we want the image to portray a more lively forest. By clicking and dragging the white pointer slider in the histogram to the left until a value of 210 is reached, the number of white tones in the image will increase, making the image a little brighter.
You can change what is defined as black or white in an image using the Levels Eyedropper tools located in the bottom right-hand portion of the Levels dialog box. To designate what is black and white in an image, select the appropriate eyedropper and click on a color on the image itself. For our example, we'll select the Highlight Eyedropper, the right-hand one, and select the position circled in red. This creates a brilliant aura over the forest in a higher contrasting tone. If you want the trees to be a little more reddish, we can give it a blush by selecting the Midtones Eyedropper, the central one, and clicking on the position circled in red here. As you can see, the original image on the left has now been transformed into a lush, vibrant forest on the right.
The Curves dialog box is accessed by Image > Adjust > Curves, or <Ctrl>M (Windows) or <Cmd>M (Mac OS). Manipulating curves is similar to manipulating levels, but you are offered greater control when adjusting image tones. As you can see by the gradients, you can also adjust the shadows, midtones, and highlights. When working with curves, you can also add points for increased accuracy. To do this, click on the diagonal line and drag to the desired value. To add another point, click on another area of the line and repeat the procedure until you get the desired affect. The Curves Eyedropper work the same as the Levels Eyedroppers.
The Color Balance dialog box allows you to specifically changes the tonal colors of the image. Clicking and dragging the sliders to the left or right will change the tonal color of the whole image to that specific color. Again, you can adjust the shadows, midtones, or highlights of an image. The Color Balance dialog, however, does not have Eyedropper tools because you are changing the colors directly.
Brightness and Contrast
The Brightness and Contrast dialog is simple and is used just as often as the other image adjust features, if not more, for quick fixes. Simply, the higher the Brightness value, the brighter and lighter the image will be. The same goes for the Contrast value. A high Contrast value would imply that the whites are whiter and the darks are darker.