The first step in retouching a photograph in Photoshop is to make sure that the image is the correct resolution. The termresolution refers to the number of small squares known aspixels that describe an image and establish its detail. Resolution is determined by pixel dimensions, or the number of pixels along the width and height of an image.
In computer graphics, there are different types of resolution:
The number of pixels per unit of length in an image is called the image resolution, usually measured in pixels per inch (ppi). An image with a high resolution has more pixels (and therefore a larger file size) than an image of the same dimensions with a low resolution. Images in Photoshop can vary from high resolution (300 ppi or higher) to low resolution (72 ppi or 96 ppi).
The number of pixels per unit of length on a monitor is themonitor resolution, also usually measured in pixels per inch (ppi). Image pixels are translated directly into monitor pixels. In Photoshop, if the image resolution is higher than the monitor resolution, the image appears larger onscreen than its specified print dimensions. For example, when you display a 1-x-1-inch, 144-ppi image on a 72-ppi monitor, the image fills a 2-x-2-inch area of the screen.
4 x 6 inches at 72 ppi; file size 364.5
100% onscreen view
4 x 6 inches at 200 ppi; file size 2.75 MB
100% onscreen view
The number of ink dots per inch (dpi) produced by a platesetter or laser printer is the printer, or output, resolution. Of course, higher-resolution printers combined with higher-resolution images generally produce the best quality. The appropriate resolution for a printed image is determined both by the printer resolution and by the screen frequency, or lines per inch (lpi), of the halftone screens used to reproduce images.
Keep in mind that the higher the image resolution, the larger the file size and the longer the file takes to download from the Web.
For more information on resolution and image size, see Adobe Photoshop Help
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) on the tool options bar to open Adobe Bridge.)
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), and draw a selection border around the yellow tulip in the left foreground of the image. Don’t worry about making a perfect selection, but be sure to include all of the yellow flower.)
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), click anywhere in the yellow tulip in the image window to sample that color.)
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) to sample other areas of the yellow tulip until the entire flower is selected and highlighted in the mask display in the Replace Color dialog box.)
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) and click those areas in either the image window or in the Replace Color mask display to remove those stray pixels. (It’s OK if a few remain in the selection.))
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You got a jump start on learning about the zoom tool while we were studying the status bar in the last section. Now let's explore more of the Photoshop toolbox. If you have the Quick Reference Card that came with Photoshop, it would be a good idea to locate it now. If you cannot locate a copy, Version 6.0 users can find a PDF file of the Quick Reference card on the main level of your Photoshop installation CD. Version 5.x users can find a diagram of the toolbox and all hidden tools on page 25 of the Photoshop 5.0 User Guide.
When you look at the toolbox, notice how some of the buttons have a tiny arrow in the lower right corner. This arrow indicates that other tools are hidden under that tool. To access the other tools, click and hold down on a button and the other tools will pop out. Try this now by clicking on the rectangle marquee tool and changing to the elliptical marquee tool. The hidden marquee tools are shown here.
Now hold your cursor over one of the buttons and you should see a tooltip appear that tells you the name of the tool and its keyboard shortcut. All the marquee tools have a shortcut of M. An easier way to switch between the different hidden tools is to use the keyboard shortcut along with the Shift key modifier. For the marquee tools, the Shift-M combination toggles between the rectangular and elliptical marquee tools. The single row marquee tools are less often used and must be selected from the toolbox flyout. Another shortcut for cycling through the hidden tools is to 
Moving down in the toolbox, we come to the color swatches. This is where the foreground and background colors are displayed. The tiny arrow to the top right allows you to swap foreground and background colors. The tiny black and white swatch symbol to the lower left allows you to reset the colors to the default of black foreground and white background. Hold your cursor over those two areas to learn the keyboard shortcuts. To change a color, simply click on either the foreground or background color swatch and select a new color in the color picker. Experiment by changing the foreground and background colors and then resetting them back to defaults.
The next two buttons on the toolbox allow you to toggle between quick mask and selection mode. We'll learn more about this later in future lessons.
Below that you have a set of three buttons that allow you to change the appearance of the workspace. Hold your cursor over each button to see what it does. Notice the keyboard shortcut for all three is F. Hitting F repeatedly toggles between all three modes. Try it now.