Crop
Description
Assumes the image holds a non-rectangular shape that is padded with a uniform color and replaces all padding pixels with void.
Since the source image is read scanline after scanline, cropping is performed locally for each scanline: Beginning at the left and right image borders, all pixels having the same color as the color parameter are replaced with void until a consecutive run of pixels having different colors is found (see skip). The following figures illustrates this: Pixels that have the same color as the color parameter are shown as '.' characters, all others are indicated with X:
+-----------------------------------------------------------------------+ |.......................................................................| |.......................................................................| |............................XXX........................................| |...........................XXXXX.......................................| |.........................XXXXXXX.......................................| |.......................XXXXXXXXX.......................................| |.....................XXXXXXXXXXX.......................................| |...................XXXXXXXXXXXXXX......................................| |.................XXXXXXXXXXXXXXXX......................................| |................XXXXXXXXXXXXXXXXX......................................| |...............XXXXXXXXXXXXXXXXXXX.....................................| |................XXXXXXXXXXXXXXXXXXX....................................| |.................XXXXXXXXXXXXXXXXXXXXX.................................| |...................XXXXXXXXXXXXXXXXXXXXXXX.....X.......................| |...............XXXXXXXXXX..XXXXXXXXXXXXXXXXXXXXXXXXXXX.................| |..........XXXXXXXXXXXX.......XXXXXXXXXXXXXXXXXXXXXXXXXXX...............| |.............XXXXXXX..........XXXXXXXXXXXXXXXXXXXXXXXXXX...............| |...............XXX.............XXXXXXXXXXXXXXXXXXXXXXXX................| |................................XXXXXXXXXXXXXXXXXXXXX..................| |................................XXXXXXXXXXXXXXXXX......................| |...................................XXXXXXX.............................| |.......................................................................| |.......................................................................| |.......................................................................| |.......................................................................| +-----------------------------------------------------------------------+
The cropped image will look like this (whitespace represents void pixels):
+-----------------------------------------------------------------------+ | | | | | XXX | | XXXXX | | XXXXXXX | | XXXXXXXXX | | XXXXXXXXXXX | | XXXXXXXXXXXXXX | | XXXXXXXXXXXXXXXX | | XXXXXXXXXXXXXXXXX cropped because | | XXXXXXXXXXXXXXXXXXX of skipped pixels | | XXXXXXXXXXXXXXXXXXX | | | XXXXXXXXXXXXXXXXXXXXX V | | XXXXXXXXXXXXXXXXXXXXXXX | | XXXXXXXXXX..XXXXXXXXXXXXXXXXXXXXXXXXXXX | | XXXXXXXXXXXX.......XXXXXXXXXXXXXXXXXXXXXXXXXXX | | XXXXXXX..........XXXXXXXXXXXXXXXXXXXXXXXXXX | | XXX.............XXXXXXXXXXXXXXXXXXXXXXXX | | ^ XXXXXXXXXXXXXXXXXXXXX | | | XXXXXXXXXXXXXXXXX | | not reachable XXXXXXX | | from left or | | right border | | | | | +-----------------------------------------------------------------------+
Cropping will not change the image size or modify the georeference.