nearblack Man page

nearblack General Commands Manual nearblack

NAME

nearblack – nearblack convert nearly black/white borders to black

SYNOPSIS

nearblack [-of format] [-white | [-color c1,c2,c3…cn]*] [-near dist] [-nb non_black_pixels] [-setalpha] [-setmask] [-o outfile] [-q] [-co “NAME=VALUE”]* infile

DESCRIPTION

This utility will scan an image and try to set all pixels that are
nearly or exactly black, white or one or more custom colors around the
collar to black or white. This is often used to ‘fix up’ lossy
compressed airphotos so that color pixels can be treated as transparent
when mosaicking.

-o outfile:
The name of the output file to be created. Newly created files are
created with the HFA driver by default (Erdas Imagine – .img)

-of format:
(GDAL 1.8.0 or later) Select the output format. Use the short
format name (GTiff for GeoTIFF for examle).

-co ‘NAME=VALUE’:
(GDAL 1.8.0 or later) Passes a creation option to the output format
driver. Multiple -co options may be listed. See format specific
documentation for legal creation options for each format. Only
valid when creating a new file

-white:
Search for nearly white (255) pixels instead of nearly black
pixels.

-color c1,c2,c3…cn:
(GDAL >= 1.9.0) Search for pixels near the specified color. May be
specified multiple times. When -color is specified, the pixels that
are considered as the collar are set to 0.

-near dist:
Select how far from black, white or custom colors the pixel values
can be and still considered near black, white or custom color.
Defaults to 15.

-nb non_black_pixels:
number of non-black pixels that can be encountered before the
giving up search inwards. Defaults to 2.

-setalpha:
(GDAL 1.8.0 or later) Adds an alpha band if the output file is
specified and the input file has 3 bands, or sets the alpha band of
the output file if it is specified and the input file has 4 bands,
or sets the alpha band of the input file if it has 4 bands and no
output file is specified. The alpha band is set to 0 in the image
collar and to 255 elsewhere.

-setmask:
(GDAL 1.8.0 or later) Adds a mask band to the output file, or adds
a mask band to the input file if it does not already have one and
no output file is specified. The mask band is set to 0 in the image
collar and to 255 elsewhere.

-q:
(GDAL 1.8.0 or later) Suppress progress monitor and other non-error
output.

infile:
The input file. Any GDAL supported format, any number of bands,
normally 8bit Byte bands.

The algorithm processes the image one scanline at a time. A scan ‘in’
is done from either end setting pixels to black or white until at least
‘non_black_pixels’ pixels that are more than ‘dist’ gray levels away
from black, white or custom colors have been encountered at which point
the scan stops. The nearly black, white or custom color pixels are set
to black or white. The algorithm also scans from top to bottom and from
bottom to top to identify indentations in the top or bottom.

The processing is all done in 8bit (Bytes).

If the output file is omitted, the processed results will be written
back to the input file – which must support update.

AUTHORS
Frank Warmerdam warmerdam@pobox.com

GDAL Tue Apr 5 2016 nearblack

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