pfsabsolute(1) General Commands Manual pfsabsolute(1)NAME
pfsabsolute - Convert luminance in images to absolute measure
SYNOPSIS
pfsabsolute <dest Y> [<src Y>] [--verbose] [--help]
DESCRIPTION
pfsabsolute applies all necessary operations to convert an image from relative luminance (tag LUMINANCE is RELATIVE) or display-dependent
luma (tag LUMINANCE is DISPLAY) to absolute luminance values. When the luminance in an image is absolute (tag LUMINANCE set to ABSOLUTE),
the Y channel represents physical luminance in cd/m^2. Absolute luminance levels are useful for some tone mapping algorithms and also for
image or video compression.
The argument <dest Y> denotes the level of luminance that relative luminance <src Y> should be rescaled to. The luminance is in fact multi-
plied by the ratio <dst Y>/<src Y>. <src Y> is normally relative luminance checked with pfsview in the spot where the absolute luminance
<dest Y> is measured, known or guessed. If <src Y> is omitted, the value 1 is assumed, so <dest Y> is just a scaling factor.
In case if display-depended luma (tag LUMINANCE is DISPLAY), the inverse gamma correction is applied (assuming sRGB color space). In such
case <dest Y> is usually the maximum luminance of a display (e.g. 80 cd/m^2).
This command always sets LUMINANCE tag to ABSOLUTE.
EXAMPLES
pfsin memorial.hdr | pfsabsolute 20 0.04 | pfsview
Multiply luminance in memorial image, so that relative luminance 0.04 becomes 20 cd/m^2. Normally, the value 0.04 is check using
pfsview in the spot, where the absolute luminance (which equals in this case 20 cd/m^2) is known.
pfsin lena.png | pfsabsolute 80 | pfsview
Convert lena image from sRGB color space to absolute XYZ, assuming maximum luminance of the monitor 80 cd/m^2.
SEE ALSO pfsgamma(1)pfsinppm(1)BUGS
Please report bugs and comments to Rafal Mantiuk <mantiuk@mpi-sb.mpg.de>.
pfsabsolute(1)
Check Out this Related Man Page
pfsinppm(1) General Commands Manual pfsinppm(1)NAME
pfsinppm - Load images or frames in PBM formats
SYNOPSIS
pfsinppm (<file> [--linear] [--absolute <max_lum>] [--frames <range>] [--skip-missing]) [<file>...]
DESCRIPTION
pfsinppm command loads images in PBM formats (PPM, PNM or PGM) and writes pfs stream to the standard output. The pfs stream is usually
piped to another program for further processing. To detect the format automatically based on the extension, use pfsin command. For more
information on PBM formats, refer to the NetPBM web page (http://netpbm.sourceforge.net/).
Note that PPM or PNM images are low dynamic range. Therefore pixel values (0-255) are scaled to 0-1 before storing them in pfs stream. Sim-
ilarly, before writing low dynamic range image from pfs stream, pixel values are multiplied by 255. By default, the 'LUMINANCE' tag is set
to 'DISPLAY'. The '--linear' switch can force the inverse sRGB transformation and provide linear data. In this case the 'LUMINANCE' tag is
set to 'RELATIVE'. '--absolute' switch can be used to convert pixels to absolute luminance values.
To read images from standard input use a single dash '-' instead of filename. The images are read until EOF is reached.
Each file can contain a %d pattern, which is substituted with frame numbers. The pattern has the same syntax as C printf command. For exam-
ple, you can use %04d to make the frame number four digit with proceedings zeros. See the OPTIONS section below for details.
OPTIONS --frames <range>
Range is given in mathlab / octave format:
startframe:step:endframe
Frame numbers start with startframe (default 0), are increased by step (default 1) and stop at endframe You can skip one of those
values, for example 1:100 for frames 1,2,...,100 and 0:2: for frame 0,2,4,... up to the last file that exists.
--skip-missing
Skip up to ten frames in a row if corresponding files are missing. Otherwise the program stops reading sequence at the first file
that does not exists. This switch does not apply to the first frame in a sequence. This switch can be useful if there is a rendered
animation where some of the frame has not been generated.
--linear, -l
Converts pixel values to linear luminance (XYZ), assuming the sRGB color space for the input image. The maximum pixel value
(255,255,255) is mapped to Y=1. LUMINANCE tag is set to RELATIVE.
--absolute <max_lum>, -a <max_lum>
--absolute converts pixel values to an absolute linear luminance (XYZ), that is the color space, in which channel Y contains lumi-
nance given in cd/m^2. The sRGB color space is assumed for the input image. The maximum pixel value (255,255,255) is mapped to
Y=<max_lum>. <max_lum> is typically set to 80 [cd/m^2] for a CRT monitor. LUMINANCE tag is set to ABSOLUTE. --absolute process
images almost the same as --relative, but additionally it scales all pixels by <max_lum>.
EXAMPLES
pfsinppm frame%04d.ppm --frames 0:10 | pfsview
Read frames from files frame0000.ppm, frame0001.ppm, ..., frame0010.ppm and show them using pfsview.
BUGS
Please report bugs and comments on implementation to the discussion group http://groups.google.com/group/pfstools
SEE ALSO pfsin(1), pfsout(1)pfsinppm(1)