man page of webhdr_jpgheatmap


webhdr_jpgheatmap - Produce image from an exposure-bracketed JPG sequence indicating pixels from which reliable photometric HDR information cannot be derived.


webhdr_jpgheatmap [options] file1.jpg file2.jpg .. fileN.jpg

Options: --help brief help message --man full documentation --versions print version info of loaded modules --debug output intermediate image files for debugging -d|--dim dimensions of output image -u|--upper upper threshold -l|--lower lower threshold -o|--output output file name


webhdr_jpgheatmap will read an exposure-bracketed sequence of digital photographs and analyse the pixel values in the brightest and darkest photographs.

Pixels which lie below the lower threshold in the brightest image or above the upper threshold in the darkest image are shown in blue and red, resp. against a background which is a contrast-reduced and brightness-increased version of the photograph whose average brightness is closest to 50%.

The thresholding is done separately for the Red, Green, and Blue channels of the source images.

webhdr_jpgheatmap is meant to produce relatively small preview images. All operations are 'infectious' in that channel-merging and downsampling will produce the worst possible result, i.e. the highest number of hot or cold pixels. Resizing is done with a cubic filter. This is slower than linear sampling, but doesn't result in the artefacts that a linear operator is prone of.



Print a brief help message and exit.


Print the manual page and exit.


Print version information of the program, loaded modules, Perl, and the OS.


Write out the intermediate image files for debugging. This also prints additional information that might be helpful for troubleshooting.


Image dimensions. The output image will be resized so that its longest dimension is equal to this value. The default for this option is 512 pixels.


Output file. The default here is 'heatmap.png', which the software will attempt to write to the working directory.


Upper threshold. This level is the range between 100 and 255, and marks the bright pixels on the darkest photograph above which reliable photometric information cannot be determined. The default for this is 228. Pixels above this value will be shown as 'hot' pixels. The thresholds used to be 20 (upper) and 200 (lower, see below) See


Lower threshold. This is the level of the darkest pixels on the brightest photograph below which reliable photometric information cannot be determined. The default for this is 27. Pixels below this value will be shown as 'cold' pixels.


To generate an image whose largest dimension is 400 px and output the result to a file named hotcold.png:

  webhdr_jpgheatmap -o hotcold.png --dim 400 sequences/DSCN286?.JPG


Perl bindings for ImageMagick (


webhdrtools's lib directory needs to be in PERL5LIB



Copyright 2013 Axel Jacobs

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see <>.