NAME

       giftool - GIF transformation tool

SYNOPSIS

       giftool [-a aspect] [-b bgcolor] [-d delaytime] [-i interlacing] [-n imagelist]
               [-p left,top] [-s width,height] [-t transcolor] [-u sort-flag] [-x disposal]
               [-z sort-flag]

DESCRIPTION

       A filter for transforming GIFS. With no options, it's an expensive copy of a GIF in
       standard input to standard output. Options specify filtering operations and are performed
       in the order specified on the command line.

       The -n option selects images, allowing the tool to act on a subset of images in a
       multi-image GIF. This option takes a comma-separated list of decimal integers which are
       interpreted as 1-origin image indices; these are the images that will be acted on. If no
       -n option is specified, the tool will select and transform all images.

       The -b option takes a decimal integer argument and uses it to set the (0-origin) screen
       background color index.

       The -f option accepts a printf-style format string and substitutes into it the values of
       image-descriptor and graphics-control fields. The string is formatted and output once for
       each selected image. Normal C-style escapes \b, \f, \n, \r, \t. \v, and \xNN are
       interpreted; also \e produces ESC (ASCII 0x1b). The following format cookies are
       substituted:

       %a
           Pixel aspect byte.

       %b
           Screen background color.

       %d
           Image delay time

       %h
           Image height (y dimension)

       %n
           Image index

       %p
           Image position (as an x,y pair)

       %s
           Screen size (as an x,y pair)

       %t
           Image transparent-color index

       %u
           Image user-input flag (boolean)

       %v
           GIF version string

       %w
           Image width (x dimension)

       %x
           Image GIF89 disposal mode

       %z
           Image's color table sort flag (boolean, false if no local color map)

       Boolean substitutions may take a prefix to modify how they are displayed:

       1
           "1" or "0"

       o
           "on" or "off"

       t
           "t" or "f"

       y
           "yes" or "no"

       Thus, for example, "%oz" displays image sort flags using the strings "on" and "off". The
       default with no prefix is numeric.

       The -a option takes an unsigned decimal integer argument and uses it to set the
       aspect-ratio bye in the logical screen descriptor block.

       The -b option takes an unsigned decimal integer argument and uses it to set the background
       color index in the logical screen descriptor block.

       The -d option takes a decimal integer argument and uses it to set a delay time, in
       hundredths of a second, on selected images.

       The -i option sets or clears interlaccing in selected images. Acceptable arguments are
       "1", "0", "yes", "no", "on", "off", "t", "f"

       The -p option takes a (0-origin) x,y coordinate-pair and sets it as the preferred
       upper-left-corner coordinates of selected images.

       The -s option takes a (0-origin) x,y coordinate-pair and sets it as the expected display
       screen size.

       The -t option takes a decimal integer argument and uses it to set the (0-origin) index of
       the transparency color in selected images.

       The -u option sets or clears the user-input flag in selected images. Acceptable arguments
       are "1", "0", "yes", "no", "on", "off", "t", "f".

       The -x option takes a decimal integer argument and uses it to set the GIF89 disposal mode
       in selected images.

       The -z option sets or clears the color-table sort flag in selected images. Acceptable
       arguments are "1", "0", "yes", "no", "on", "off", "t", "f".

       Note that the -a, -b, -p, -s, and -z options are included to complete the ability to
       modify all fields defined in the GIF standard, but should have no effect on how an image
       renders on browsers or modern viewers.

AUTHOR

       Eric S. Raymond.