ximage vs. pcond

Hi ---

Why does pcond produce a (slightly) different tonemapping from ximage -e auto ? The contrast is better with ximage and I would like to take the output as my final image. Is there an easy way to do this ? I use the default values for all options.

A few things I've tried:

ximage -e auto hdr.pic
# produces nice high-contrast rendition of image

pcond hdr.pic ldr.pic
ximage ldr.pic
# tonemapping is inferior

ra_tiff ldr.pic ldr.tif
xview ldr,tif
# tonemapping is still not good. This suggests that it is not the 2.2 gamma of ximage that makes the images look good, because ra_tiff also uses 2.2 gamma correction (according to the documentation).

  ximage -e auto ldr,pic
# tonemapping is better, but still not quite as good as the original.

Thanks for any tips!
Roland Fleming

r o l a n d f l e m i n g p h d
r e s e a r c h s c i e n t i s t

m a x p l a n c k i n s t i t u t e f o r b i o l o g i c a l c y b e r n e t i c s
s p e m a n n s t r . 3 8
7 2 0 7 6 t u e b i n g e n
g e r m a n y

t e l :: [ + 4 9 ] 0 7 0 7 1 6 0 1 - 6 0 9

Hi Roland,

Pcond and ximage use completely different implementations of the histogram adjustment operator. By design, they should be reasonably well matched if you use the default options for pcond and "ximage -e auto", or "pcond -s -c" to match "ximage -e human". However, because the histograms are computed in a slightly different way, you can sometimes get discrepancies.

If you want your output to match the ximage display, I suggest you use normtiff rather than pcond, which performs tone-mapping using the same algorithms in ximage, and converts to a 24-bit RGB TIFF output.

-Greg

The bad thing about Radiance is its enormous depth.

The good thing about Radiance is its enormous depth.

Would you believe I've never used this program, normtiff?! Don't answer
that. I've always run pcond -h then used ra_tiff to get tiffs that I
could print. And wouldn't you know it, just today I'm working on some
images that needed to go through this process; I just used normtiff
instead and they look *much* better (and it's one less step, to boot).
Bliss.

···

On Mon, April 18, 2005 12:27 pm, Gregory J. Ward said:

If you want your output to match the ximage display, I suggest you use
normtiff rather than pcond, which performs tone-mapping using the same
algorithms in ximage, and converts to a 24-bit RGB TIFF output.

--
Rob Guglielmetti
www.rumblestrip.org

Bear in mind that normtiff (and ximage -e auto) don't do everything pcond can do. In particular, they cannot simulate human loss in acuity and veiling glare, so if you really want "pcond -h", don't expect "normtiff -h" to work as a substitute. Also, if you are converting animation frames and want all the frames to use the same tone-mapping, pcond -I works with the output of phisto, whereas there is no such option in normtiff.

Just had to throw in some caveats.
-Greg

···

From: "Rob Guglielmetti" <[email protected]>
Date: April 18, 2005 11:17:31 AM PDT

On Mon, April 18, 2005 12:27 pm, Gregory J. Ward said:

If you want your output to match the ximage display, I suggest you use
normtiff rather than pcond, which performs tone-mapping using the same
algorithms in ximage, and converts to a 24-bit RGB TIFF output.

The bad thing about Radiance is its enormous depth.

The good thing about Radiance is its enormous depth.

Would you believe I've never used this program, normtiff?! Don't answer
that. I've always run pcond -h then used ra_tiff to get tiffs that I
could print. And wouldn't you know it, just today I'm working on some
images that needed to go through this process; I just used normtiff
instead and they look *much* better (and it's one less step, to boot).
Bliss.

--
Rob Guglielmetti
www.rumblestrip.org

Yes, I noticed in the manpage that "normtiff -h" is a subset of "pcond
-h". In my case here, it worked well because these are nighttime exterior
images but made with crude representations for the luminaires, and pcond's
veiling glare treatment was not desirable for the purposes of these images
(and for some reason switching that off (pcond -h -v-) gave me some odd
artifacts). It was about then that your email about normtiff showed up.

Thanks for the heads up though. There should be a warning on the download
page for Radiance: "warning, entering DEEP water..." (or deep
*something*.)

···

On Mon, April 18, 2005 2:33 pm, Gregory J. Ward said:

Bear in mind that normtiff (and ximage -e auto) don't do everything
pcond can do. In particular, they cannot simulate human loss in acuity
and veiling glare, so if you really want "pcond -h", don't expect
"normtiff -h" to work as a substitute. Also, if you are converting
animation frames and want all the frames to use the same tone-mapping,
pcond -I works with the output of phisto, whereas there is no such
option in normtiff.

--
Rob Guglielmetti
www.rumblestrip.org