Image Essentials; About Bitmap Images; About Vector Graphics; Combining Vector Graphics And Bitmap Images - Adobe Photoshop CS6 User Manual

Image essentials

About bitmap images

About vector graphics

Combining vector graphics and bitmap images

Color channels
Bit depth
Convert between bit depths
About bitmap images
Bitmap images—technically called raster images—use a rectangular grid of picture elements (pixels) to represent images. Each pixel is assigned a
specific location and color value. When working with bitmap images, you edit pixels rather than objects or shapes. Bitmap images are the most
common electronic medium for continuous-tone images, such as photographs or digital paintings, because they can more efficiently represent
subtle gradations of shades and color.
Bitmap images are resolution-dependent—that is, they contain a fixed number of pixels. As a result, they can lose detail and appear jagged if they
are scaled to high magnifications on-screen or if they are printed at a lower resolution than they were created for.
Example of a bitmap image at different levels of magnification
Bitmap images sometimes require large amounts of storage space, and often need to be compressed to keep file sizes down when used in certain
Creative Suite components. For instance, you compress an image file in its original application before you import it into a layout.
Note: In Adobe Illustrator, you can create bitmap effects in your artwork using effects and graphic styles.
About vector graphics
Vector graphics (sometimes called vector shapes or vector objects) are made up of lines and curves defined by mathematical objects called
vectors, which describe an image according to its geometric characteristics.
You can freely move or modify vector graphics without losing detail or clarity, because they are resolution-independent—they maintain crisp edges
when resized, printed to a PostScript printer, saved in a PDF file, or imported into a vector-based graphics application. As a result, vector graphics
are the best choice for artwork, such as logos, that will be used at various sizes and in various output media.
The vector objects you create using the drawing and shape tools in Adobe Creative Suite are examples of vector graphics. You can use the Copy
and Paste commands to duplicate vector graphics betweenCreative Suite components.
Combining vector graphics and bitmap images
When combining vector graphics and bitmap images in a document, it's important to remember that how your artwork looks on-screen isn't always
how it will look in its final medium (whether commercially printed, printed on a desktop printer, or viewed on the web). The following factors
influence the quality of your final artwork:
Transparency Many effects add partially transparent pixels to your artwork. When your artwork contains transparency, Photoshop performs a
process called flattening before printing or exporting. In most cases, the default flattening process produces excellent results. However, if your
artwork contains complex, overlapping areas and you require high-resolution output, you will probably want to preview the effects of flattening.
Image Resolution The number of pixels per inch (ppi) in a bitmap image. Using too low a resolution for a printed image results in pixelation—
output with large, coarse-looking pixels. Using too high a resolution (pixels smaller than what the output device can produce) increases the file size
without increasing the quality of the printed output, and slows the printing of the artwork.
Printer resolution and screen frequency The number of ink dots produced per inch (dpi) and the number of lines per inch (lpi) in a halftone
screen. The relationship between image resolution, printer resolution, and screen frequency determines the quality of detail in the printed image.
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