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#!/usr/bin/env slsh
% This script prints the width and height of one or more jpeg image files.
if (__argc < 2)
{
() = fprintf (stderr, "Usage: %s files....\n", path_basename (__argv[0]));
exit (1);
}
private variable M_SOF0 = 0xC0; %/* Start Of Frame N */
private variable M_SOF1 = 0xC1; %/* N indicates which compression process */
private variable M_SOF2 = 0xC2; %/* Only SOF0-SOF2 are now in common use */
private variable M_SOF3 = 0xC3; %
private variable M_SOF5 = 0xC5; %/* NB: codes C4 and CC are NOT SOF markers */
private variable M_SOF6 = 0xC6; %
private variable M_SOF7 = 0xC7; %
private variable M_SOF9 = 0xC9; %
private variable M_SOF10 = 0xCA; %
private variable M_SOF11 = 0xCB; %
private variable M_SOF13 = 0xCD; %
private variable M_SOF14 = 0xCE; %
private variable M_SOF15 = 0xCF; %
private variable M_SOI = 0xD8; %/* Start Of Image (beginning of datastream) */
private variable M_EOI = 0xD9; %/* End Of Image (end of datastream) */
private variable M_SOI = 0xD8; % Start Of Image (beginning of datastream)
private define read_nbytes (fp, n)
{
variable b;
if (n != fread_bytes (&b, n, fp))
throw ReadError, "Failed to read $n bytes"$;
return b;
}
private define read_ushort (fp)
{
return unpack (">H", read_nbytes (fp, 2));
}
private define open_jpg_file_for_read (file)
{
variable fp = fopen (file, "rb");
variable b = read_nbytes (fp, 2);
if ((b[0] != 0xFF) or (b[1] != M_SOI))
return NULL;
return fp;
}
private define next_marker (fp)
{
variable c = read_nbytes (fp, 1);
while (c != 0xFF)
c = read_nbytes (fp, 1);
% Remove pad bytes
do
c = read_nbytes (fp, 1);
while (c == 0xFF);
return c;
}
private define skip_variable (fp)
{
variable len = read_ushort (fp);
if (len < 2)
throw DataError, "Erroneous JPEG marker length";
len -= 2;
while (len > 512)
{
() = read_nbytes (fp, 512);
len -= 512;
}
() = read_nbytes (fp, len);
}
public define jpeg_size (file, width, height)
{
variable fp = open_jpg_file_for_read (file);
if (fp == NULL)
return -1;
variable is_sof = UChar_Type[256];
is_sof[M_SOF0] = 1;
is_sof[M_SOF1] = 1;
is_sof[M_SOF2] = 1;
is_sof[M_SOF3] = 1;
is_sof[M_SOF5] = 1;
is_sof[M_SOF6] = 1;
is_sof[M_SOF7] = 1;
is_sof[M_SOF9] = 1;
is_sof[M_SOF10] = 1;
is_sof[M_SOF11] = 1;
is_sof[M_SOF13] = 1;
is_sof[M_SOF15] = 1;
while (0 == is_sof[next_marker(fp)])
{
skip_variable (fp);
}
variable len = read_ushort (fp);
variable data_precision = read_nbytes (fp, 1);
variable h = read_ushort (fp);
variable w = read_ushort (fp);
@width = w;
@height = h;
return 0;
}
private define main ()
{
variable file;
foreach file (__argv[[1:]])
{
try
{
variable width, height;
if (-1 == jpeg_size (file, &width, &height))
{
() = fprintf (stderr, "%s is not a jpeg file\n", file);
continue;
}
() = fprintf (stdout, "%s: %ux%u\n", file, width, height);
}
catch ReadError, DataError:
() = fprintf (stderr, "Caught error processing %s ...skipped\n", file);
}
exit (0);
}
main ();
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