Data Compression


Criteria

Survey Formats

Basics

Compression Methods

Data Formats


Run Length Encoding

General Principle

Control Characters

RLE for Image Data

Implementations

MS-Windows .bmp RLE8

Encoded Mode

Absolute Mode

Marker

Example "B"

MS-Windows .bmp RLE4


Glossary

Index


Download


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Marker


Marker will be initiated by the value 0 immediately followed by the byte value 0, 1, or 2 identifying the three markers available: "End of Line", "End of Bitmap" and "Delta".


Coding scheme marker:




End of Line (00 00)
The end of line marker indicates that the next code will apply to a new line. For the rest of the current line no further information is available. The default background colour has to be assigned to remaining pixels.

End of Bitmap (00 01)
The end of bitmap marker indicates the end of encoded data. Remaining parts will take over the background colour.

Delta (00 02)
The delta marker indicates a jump relative to the current position. The two bytes following quantify an unsigned horizontal and vertical offset. The next code words will be applied to the new position; the part in between will get the background colour.

Examples:

 encoded        decoded
 00 00          end of line
 00 02 0A B0    Delta-X = 10  pixel
                Delta-Y = 176 lines
 00 01          end of bitmap

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MS-Windows .bmp RLE8 Absolute Mode Example B compressed according to RLE8