On Wed, 29 Aug 2007, Brian Walters wrote:
> Quoting Cory Papenfuss <[EMAIL PROTECTED]>:
>
>> Irfanview is based on dcraw for its RAW conversion. I've had
>> issues with dcraw in doing starry-night conversions because of the
>> way it
>> decides on the white point. By default, I think it chooses the
>> white
>> point at the luminosity of the 99th percentile of the photo. Thus,
>> by
>> default, 1% of the pixels are blown out.
>>
>> I've changed that setting on my version of it a few times to make
>>
>> it 99.9th or 99.99th percentile for star photos. Works great.
>
>
> That's interesting. I've had a similar experience with the
> interpretation of Raw files in Studioline Photo Classic, a program that
> I use for cataloging images. It also uses dcraw. The raw conversion of
> photos I took some months ago of Comet McNaught are all blown out badly
> in the Studioline conversions.
>
> I don't quite understand the setting changes you made to Irfanview. Can you
> elaborate?
>
>
> Cheers
>
> Brian
>
Since I'm a linux guy and compiled dcraw from Dave Coffin's C
source code, I simply changed that one line to a different number.
Probably doesn't help most people who use programs *based* on dcraw.
The originial line of code read
perc = width * height * 0.01; /* 99th percentile white point */
... which I changed to
perc = width * height * 0.001; /* 99.9th percentile white point */
or
perc = width * height * 0.0001; /* 99.99th percentile white point */
I could have done it by manipulating the blackpoint and brightness
settings instead, but I would have had to do that by hand. I generally
run through all my RAW conversions with everything set up on "auto," and
only fine-tune the ones that deserve special attention. Re-compiling the
source allowed me to use the same batch mode script, just have a modified
dcraw good for star photos.
Sorry, that probably doesn't help much.
-Cory
--
*************************************************************************
* Cory Papenfuss, Ph.D., PPSEL-IA *
* Electrical Engineering *
* Virginia Polytechnic Institute and State University *
*************************************************************************
--
PDML Pentax-Discuss Mail List
[email protected]
http://pdml.net/mailman/listinfo/pdml_pdml.net
