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
multiplied 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>.