Computer Science 1033 Topic 3 Notes

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Computer Science
Computer Science 1033A/B
Vivi Tryphonopolous

Graphics Continued Image Optimization  For printing, quality comes before file size.  For web pages, file size comes before quality, because the webpage has to be downloaded fast to be competitive. The challenge of webpage creation is to keep file size small, and maintain the quality as much as possible.  File formats: o USE:  .GIF (Graphics Interchange Format)  Commonplace image format used on the internet  Cross platform  Supports a maximum of 8-bit color scheme (256 colors)  Best for solid, flat colors, such as illustration, animation, text, and buttons.  Not best for photos, and does not support sound.  Tiny file size in comparison to .jpg  Saving an image with 24 bit color as a GIF will lower the quality immediately.  .JPG / .JPEG (Joint Photographic Experts Group):  Common image format used on the internet  Cross platform  Supports maximum of 24-bit color scheme (16 million colors)  Good for photos, computer games, screen shots, stills from movie  Best for blends of colors, softer shadow effects, subtle changes in color.  Not best for well-defined lines or sharp contrasts between colors.  Much larger size in comparison to .GIF  .PNG o DON’T USE.TIFF .BMP (uncompressed format), .RAW (digital camera uncompressed) .PSD  Compression: o Reduces the redundancy of the image data to be able to store or transmit data in an efficient form o Compress as much as possible without sacrificing quality (by losing bits information) o Lossless:  Every time the user saves a file.  Compress the original bytes into less byte without losing any of the original quality.  No information is lost. When the file is reopened, all the original information is still there.  Used by .GIF. Uses a simple technique called LZW compression to reduce the file size of images by finding repeated patterns of pixels. o Lossy:  Every time the user saves a file, they can choose to control compression  Discard selected portions of the image, which cannot be retrieved once discarded.  Used by .JPG  Attempts to find and save information about the brightness, because the human eye is more sensitive to brightness details than to fine color details  If it finds two adjacent pixels with very similar colors, it stores them as the same color, and the other color is discarded.  It is possible to select the quality (compression ratio) of the final image.
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