From: gward@lmi.net (Greg Ward)
Date: Wed, 26 Nov 2003 09:54:08 -0800
Subject: [Tiff] Re: Bug in LogLuv
In-Reply-To: <6.0.1.1.0.20031126151401.01e45d98@mail.tecgraf.puc-rio.br>
Message-ID: <88674C3A-2039-11D8-B752-000A956D40C8@lmi.net>

Hi Scuri,

> From: Antonio Scuri <scuri@tecgraf.puc-rio.br>
> Date: Wed Nov 26, 2003  9:41:40  AM US/Pacific
>
> At 14:31 26/11/2003, you wrote:
>> Thanks very much for spotting this bug!  I must have never tested or 
>> used this particular routine, because as far as I know, it's never 
>> manifested a problem.  Surely, it would have had it been applied by 
>> someone.  The 48-bit LogLuv format is not used by any of my 
>> applications for communication with the library.  I always use 
>> floating point XYZ or one of the raw LogLuv encodings.
>
>   I started using the 48-bit format, but I missunderstood the name 
> LogLuv and didn't noticed that L is infact Y. Since 16 bits were not 
> enough to hold the linear Y, I end up using the conversion to XYZ. It 
> was easier to handle the data this way.

Actually, L is still log(Y), so 16 bits is enough.  You have to use the 
formula in the tif_luv.c header comments.  I agree, though, linear XYZ 
and letting the library do the conversion is much easier!  The Radiance 
source tree includes some handy routines in the ray/src/common 
directory for fast tone-mapping from LogLuv to 24-bit RGB, and this is 
what I use in Photosphere.

>> LogLuv TIFF format is used a number of places, notably by Renderpark 
>> <http://www.linux.org/apps/AppId_4060.html> and Radiance 
>> <http://www.radiance-online.org> (via the ra_tiff converter).  It is 
>> also supported by the newest version of HDRshop 
>> <http://www.debevec.org/HDRShop/>, a program for building and 
>> manipulating high dynamic-range images, and on the Mac by Photosphere 
>> <http://www.anyhere.com>, a program for building and cataloging 
>> regular and HDR images.
>
>   Thanks for the pointers.
>
>   The version 1.03 of HDRShop that I downloaded reports compression 
> not implemented. Is there a newer version somewhere else?

I was there in Spring when Chris Tchou added this to their in-house 
version.  I was hoping it would be in the official release by now.  
Perhaps if you nudged him and Paul a bit < tchou@ict.usc.edu; 
debevec@ict.usc.edu>...

-Greg


