Bitmap Representation Divide an image into a grid Pick the - - PowerPoint PPT Presentation

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Bitmap Representation Divide an image into a grid Pick the average color in each cell (pixel) Remember that color 1 Remember Average Pixel Color 2 Wednesday, November 2, 2011 Pixels are very small! 3 428 How Much Memory 1 RGB value

SLIDE 1

Bitmap Representation

Divide an image into a grid Pick the average color in each cell (pixel) Remember that color

Remember Average Pixel Color

1 2 Wednesday, November 2, 2011

SLIDE 2

Pixels are very small! How Much Memory

428 640 1 RGB value = 3 bytes 428 x 640 x 3 = 821,760 bytes (821 KB) But file size is just 90 KB !!

3 4 Wednesday, November 2, 2011

SLIDE 3

Idea!

Remember the 256 most frequent colors used in the picture Assign each of these colors a number from 0-255 (which fits in 1 byte) Remember this 1-byte number for each pixel.

Indexed Representation

20 162 230 181 220 222 68 ... 144 ... … ... ... ... ... 144 ... ... ... ... ... ... ... ...

5 6 Wednesday, November 2, 2011

SLIDE 4

Indexed Representation

Size = size of color table + size of indexed picture Color table size = Size of indexed picture = Total = 256 * 3 bytes = 768 bytes 428 x 640 = 273,920 bytes 768 + 273,920 = 274,688 bytes 7 Wednesday, November 2, 2011