Your message dated Sun, 14 Jan 2024 08:05:02 +0100
with message-id <[email protected]>
and subject line Re: Bug#130076: netpbm: pnmgamma could use a -srgbramp option
has caused the Debian Bug report #130076,
regarding netpbm: pnmgamma could use a -srgbramp option
to be marked as done.
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--
130076: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=130076
Debian Bug Tracking System
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--- Begin Message ---
Package: netpbm
Version: 2:9.20-4
Severity: wishlist
pnmgamma has a -cieramp option which uses the transfer function of a
Rec. 709 camera. It would be nice to also have a -srgbramp option that
uses the transfer function of an sRGB monitor (sRGB was designed to
describe almost all real CRTs).
The transfer function that relates camera input to camera output is not
the same function that relates monitor output to monitor input. Given a
gamma-encoded image (such as a "standard" ppm image), pnmgamma -ungamma
-cieramp will calculate the light intensity that must have gone into
the camera to produce those image samples. But if you want to know
the light intensity that will come out of a monitor when that image is
displayed, you need something like pnmgamma -ungamma -srgbramp.
The sRGB transfer function is described here:
http://www.srgb.com/basicsofsrgb.htm
In case you're wondering, the Rec. 709 transfer function, although it
uses an exponent of 0.45, approximates a power function with an exponent
of 0.52, because of the offset. The sRGB transfer function uses an
exponent of 2.4, but approximates a power function with an exponent of
2.2 because of the offset. The product 0.52 * 2.2 = 1.144 > 1 causes
the light coming out of the monitor to have greater contrast than the
light that went into the camera, which is necessary to make it look
the same to humans, who have a different response to low light levels
(typical of monitors) than to high light levels (typical of outdoors, TV
studios, and flash photography).
-- System Information
Debian Release: 3.0
Kernel Version: Linux arwen 2.4.13 #2 SMP Fri Nov 9 04:29:32 GMT 2001 i686
unknown
Versions of the packages netpbm depends on:
ii bc 1.06-7 The GNU bc arbitrary precision calculator la
ii libc6 2.2.4-7 GNU C Library: Shared libraries and Timezone
ii libjpeg62 6b-4 The Independent JPEG Group's JPEG runtime li
ii libnetpbm9 9.20-4 Shared libraries for netpbm.
ii libpng2 1.0.12-3 PNG library - runtime
ii libtiff3g 3.5.5-6 Tag Image File Format library
ii zlib1g 1.1.3-18 compression library - runtime
--- End Message ---
--- Begin Message ---
Version: 2:10.97.00-1
On 2002-01-20 "Adam M. Costello" <[email protected]> wrote:
> Package: netpbm
> Version: 2:9.20-4
> Severity: wishlist
> pnmgamma has a -cieramp option which uses the transfer function of a
> Rec. 709 camera. It would be nice to also have a -srgbramp option that
> uses the transfer function of an sRGB monitor (sRGB was designed to
> describe almost all real CRTs).
[...]
This was added upstream in 9.25.
cu Andreas
--- End Message ---
