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Selecting Color Modes and Resolution
Selecting a Color Mode
A color mode , also known as color space , determines how Photoshop displays and prints an image. You choose a different color mode (based on models using in publishing) for different tasks. You can choose a color mode while you create a new document or change a color mode for an existing document. The common color modes include:Grayscale.
Best for printing black-and-white and duotone images. This mode uses one channel and has a maximum of 256 shades of gray.RGB (Red, Green, and Blue).
Best for online and multimedia color images. RGB are also the primary colors on a monitor.CMYK (Cyan, Magenta, Yellow, and Black).
Best for commercial printing color images.LAB (Luminosity A and B channels).
Best for performing image correction. This mode puts all grayscale information on the L channel and splits the colors on the A and B channels.For more information on color, see Chapter 8, "Understanding Colors and Channels."
Selecting Image Resolution
Photoshop works primarily with raster documents. Raster documents are images composed of pixels. A pixel is a unit of information that holds the color and detail information of the image. Thinking of a Photoshop image as a brick wall, with the individual bricks in the wall representing the individual pixels in the image, is an excellent way to envision a Photoshop document. Documents opened in Photoshop have a specific resolution. The resolution of the image, along with its width and height, represents how many pixels the image contains. Since pixels (the bricks in a wall) represent information, the more pixels a document contains, the more information Photoshop has to manipulate or enhance the image.A typical 17-inch monitor displays pixels at a resolution of 1024x768. You can figure out how many pixels are present on a monitor at 1024x768 by multiplying 1024 x 768, which equals to 786,432 pixels on the screen. The resolution is equal to how many pixels fit into each monitor inch, which is known as ppi (pixels per inch). A typical monitor displays pixels at 72ppi.To determine the size of an image in inches, we divide the pixels by the ppi. For example, for an image 1024 pixels wide, 1024 / 72 = 14.2 inches. To determine the pixels present in an image, you multiple the size by the ppi. For example, for a 3 inch image, 3 x 72 = 216. As the image resolution drops, so does the output quality of the image. Pixelization occurs when the resolution is so low that the edges of the pixel begin to appear. The higher the resolution (more pixels), the sharper the image. However, the higher the resolution, the larger the file size. To optimize the use of a file, you need to use the correct resolution for a specific task. Use 72ppi for Web pages, CD-ROMs, and Multimedia; use 150ppi for an Inkjet printer; use 200ppi for Photo printers; and use 300ppi for commercial printing.When working with images, it's always a good idea to start with a larger image size. You can always reduce the size of the image (subtract pixels) without losing any quality. If you need to enlarge an image, you run the risk of losing image quality. When you enlarge an image, the number of pixels doesn't increase as the image does, so the pixels become larger which mean a rougher image.
