Reads a Portable Network Graphics as input.
Produces a portable anymap as output.
The type of the output file depends on the input file - if its
black & white, a
pbm file is written, else if its grayscale a
pgm file, else a
Display the format of the input file and the type of the output file. If
the chunks are part of the
png-file, the alpha, transparency and gamma-values will be indicated.
Output the alpha channel or transparency mask of the image. The result is either a
pbm file or
pgm file, depending on whether different levels of transparency appear.
Compose the image with the transparency or alpha mask against a the
background. When a background chunk is available that color is taken,
else black will do.
If no background color chunck is present in the
png-file, or when another color is required this parameter can be used to set the
background color of images. This is especially useful for alpha-channel
images or those with transparency chunks. The format, to specify the color in,
is either (in the case of orange) "1.0,0.5,0.0", where the values are floats
between zero and one, or with the syntax "#RGB", "#RRGGBB" or "#RRRRGGGGBBBB"
where R, G and B are hexa-decimal numbers.
Converts the image to a new display-gamma value. When a gAMA chunk is present
png-file, the image-gamma value will be used. When not, the image-gamma is considered
to be 1.0. Based on the image-gamma and the display-gamma given with this
option the colors written to the
pnm-file will be adjusted.
Because the gammas of uncompensated monitors are around 2.6, which results
in an image-gamma of 0.45, some typical situations are:
when the image-gamma is 0.45 (use -verbose to check) and the picture is too
light, your system is gamma-corrected, so convert with "-gamma 1.0".
When no gAMA chunk is present or the image-gamma is 1.0, use 2.2 to make the
picture lighter and 0.45 to make the picture darker.
Writes the tEXt and zTXt chunks to a file, in a format as described in the
pnmtopng man-page. These chunks contain text comments or annotations.
Prints the tIME chunk to stderr.
All flags can be abbreviated to their shortest unique prefix.