pfsabsolute − Convert luminance in images to absolute measure
pfsabsolute <dest Y> [<src Y>] [--verbose] [--help]
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.
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.
Please report bugs and comments to Rafal Mantiuk <firstname.lastname@example.org>.