E-LEARNING- PHOTOSHOP CS4

Bitmap (raster) and vector:
A bitmap, or raster, image gets its detail from the number of pixels it contains, which is called resolution.
Since they depend on the number of pixels for detail, bitmap images are said to be resolution- dependent. Resolution is commonly expressed in Photoshop as the number of pixels per inch (ppi). Choose Image ➪ Image Size to see the resolution of an image.

A vector image gets its detail from shapes and lines that are mathematically calculated. The shapes and lines in vector images retain their smoothness no matter how much they are resized, regardless of how many pixels are in the image. Although there are pixels in a vector image that display color, a vector imageís detail does not depend on the number of pixels in the image. Therefore, vector images are resolution-independent.

Color mode:
The color mode of an image specifies which basic set of colors is used to make up an image. You can specify the color mode in the Image ➪ Mode menu. Colors within most color modes are stored in color channels. You can view the channels in the Channels palette. The color modes available in Photoshop are: n RGB color mode. Red, Green, and Blue are used to make up the image’s color. In 8-bpc images, tonal values range from 0 (black) to 255 (white), for each of the three colors. When the values for all three colors are equal, the resulting color is a neutral color
black, white, or a shade of gray with no color hue. RGB mode (see Figure 1.9) is used to display images on-screen because monitors use Red, Green, and Blue light to display color. It is also commonly used when color-correcting images.

CMYK color mode:
Cyan, Magenta, Yellow, and Black are used to make up the image’s color. Tonal values range from 0 percent (no color) to 100 percent (maximum amount of color) for each of the four colors. In CMYK-colors that are neutral, Magenta and Yellow have equal values and Cyan has a higher value than either Magenta or Yellow; the amount of Black determines the lightness of the color. when printing images with Cyan, Magenta, Yellow, and Black inks. Typically, RGB mode is used to color-correct images in order to preserve the maximum amount of colors and to make assigning neutral color values easier (all three color values are equal in neutral colors in RGB mode), then the image is converted to CMYK mode. But color correction can also take place in CMYK mode.

Lab color mode:
The Lab color mode (pronounced el, ay, bee, not lab) is based on a standardized way to describe color that corresponds to the way a person with normal vision sees it. It is used by color management systems
as an intermediate color reference to help accurately convert colors from one color space to another. It is sometimes used in color correction and image manipulation. Lab color (see Figure 1.11) uses the following components
to make colors: an L (lightness) component, an a component that contains green and red, and a b component that contains blue and yellow. L values range from 0 to 100; a and b values range from +127 to –128.

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