NAME

       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 air photos so that color pixels can be treated as
       transparent when mosaicing. The output format must  use  lossless  compression  if  either
       alpha band or mask band is not set.

       -o <outfile>
              The name of the output file to be created.

       -of <format>
              Select  the output format.  Starting with GDAL 2.3, if not specified, the format is
              guessed from the extension (previously was ERDAS  Imagine  .img).   Use  the  short
              format name (GTiff for GeoTIFF for example).

       -co `"NAME=VALUE"`
              Passes  a creation option to the output format driver.  Multiple -co options may be
              listed. See raster_drivers 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>
              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
              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
              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     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.

C API

       This utility is also callable from C with GDALNearblack().

       New in version 2.1.

AUTHOR

       Frank Warmerdam <warmerdam@pobox.com>

COPYRIGHT

       1998-2021

                                           Dec 27, 2021                              NEARBLACK(1)