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Image formats
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Basic terminologies…
• Pixels: Pixels are the building blocks of every digital image . • a pixel is a single point in a graphic image.
• Resolutions: We measure resolution in pixels per inch or more commonly, dots per inch (dpi).
• Resolution is the number of pixels per inch (or PPI), but it is most commonly referred to as dots per inch (DPI).
• The more pixels, or “dots,” per inch, the higher your image resolution will be.
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Memory cost of images• Large images consume large memory and make our computers
struggle. Memory cost for an image is computed from the image size.
• For a 6x4 inch image at 150 dpi, the image size is calculated as: (6 inches × 150 dpi) × (4 inches × 150 dpi) = 900 × 600 pixels • 900 × 600 pixels is 900 × 600 = 540,000 pixels. • The memory cost for this RGB color image is: • 900 × 600 × 3 = 1.6 million bytes. • The last "× 3" is for 3 bytes of RGB color information per pixel for 24
bit color (3 RGB values per pixel, one 8-bit byte for each RGB value, which totals 24 bit color).
• Assume 240 dpi is fine for our needs. 240 dpi means, there are 240 distinct pixels. Multiply 5" X 240 = 1,200 pixels. 7" X 240 = 1,680 pixels. Total number of pixels is width X length or 2,016,000 pixels.
• Mega is the short prefix for million... this is a 2 megapixel camera
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• Here's a chart to help get you started:• Resolution Max picture size w/interpolation• 640 x 480 (.3 mp) 3" x 4"• 960 x 1200 (1.1 mp) 5" x 7"• 1300 x 1600 (2 mp) 8" x 10"• 1600 x 2000 (3 mp) 9 1/2" X 11 1/2"• 2100 x 3100 (6.2 mp) 12 1/2" x 18 1/2"
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Basic image formatsImage file compression There are two types of image file compression algorithms: lossless
and loss.Lossless compression :algorithms reduce file size without losing
image quality, though they are not compressed into as small a file as a lossy compression file. When image quality is valued above file size, lossless algorithms are typically chosen.
Lossy compression :algorithms take advantage of the inherent limitations of the human eye and discard invisible information.
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Image formats.• BMP: (bitmap)
• TIFF: (Tagged Image File Format)
• PNG:(Portable Network Graphics)• GIF: (Graphics Interchange Format )
• JPEG: (Joint Photographic Experts Group )
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FORMAT NAME CHARACTERISTICS
BMP Windows bitmap Uncompressed format
TIFF Tagged Image File Format Lossless: Document scanning and
imaging format. Flexible
GIF Graphics Interchange Format
LOSSLESS: captures very limited color
PNG Portable Network Graphics Lossless: improve and replace GIF..
JPEG Joint Photographic ExpertsGroup
Lossy: big compression ratio, good for
photographic images
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• 1 bit (binary digit) = the value of 0 or 1
• 8 bits = 1 byte
• 1024 bytes = 1 kilobyte
• 1024 kilobytes = 1 megabyte
• 1024 megabytes = 1 gigabyte
• 1024 gigabytes = 1 terabyte
• 1024 terabytes = 1 petabyte