Camera saturation - image compression level
Hi, some people in France (from La main à la pâte) designed a telescope for the XO. It's a cheap ad hoc device they stick close to the camera, and it can zoom by 10x -- useful for observing, say, the moon. At this stage of the project, they have two problems: - shots of the moon are often saturated: how to reduce the gain of the camera? Ideally one would like to do this manually... - is there a way to take pictures with a higher resolution? the default compression level doesn't produce great pictures. Thanks for any feedback! -- Bastien ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Camera saturation - image compression level
On Thu, Dec 03, 2009 at 11:32:37AM +0100, Bastien wrote: some people in France (from La main à la pâte) designed a telescope for the XO. It's a cheap ad hoc device they stick close to the camera, and it can zoom by 10x -- useful for observing, say, the moon. Nice! - is there a way to take pictures with a higher resolution? the default compression level doesn't produce great pictures. Others will probably have better ideas, but maybe I can get you started. I don't think you'll be able to do really nice shots with the built-in camera as it's a simple, low-res webcam. To check whether Record causes any additional degradation, try to use some command-line V4L tool, e.g.: vgrabbj -o png -d /dev/video0 -i vga -S -f x.png For your saturation problem, you might try whether -a (maybe combined with -F 4 and/or -z number) have any effect; also try using daemon mode to capture multiple images and throw away the first one as that worked better for me than -z. v4l-info and v4l-conf (both from v4l-conf) might be useful as well. If the XO-1 and your add-on are sufficiently steady, you might try doing several shots and combining them using some filtering technique to increase the resolution (i.e. color depth, not image size - the image position isn't varied between shots); there's certainly enough noise for this to work. ;) CU Sascha -- http://sascha.silbe.org/ http://www.infra-silbe.de/ signature.asc Description: Digital signature ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Camera saturation - image compression level
Bastien - Moon photos are a problem for just about any kind of astrophotography. In addition to anything else you might try in software, the best bet is to add some kind of neutral-density filter over the scope. You might try some scrap anti-static wrap (the gray, translucent kind). It might be too dark for when the moon is less than full. Ideally you could find two pieces of cheap polarized material (inexpensive or broken polarized sunglass lenses) that you could put on top of one another while rotating one of them, making a serviceable circular polarizing filter. - Ed On Dec 3, 2009, at 5:32 AM, Bastien wrote: Hi, some people in France (from La main à la pâte) designed a telescope for the XO. It's a cheap ad hoc device they stick close to the camera, and it can zoom by 10x -- useful for observing, say, the moon. At this stage of the project, they have two problems: - shots of the moon are often saturated: how to reduce the gain of the camera? Ideally one would like to do this manually... - is there a way to take pictures with a higher resolution? the default compression level doesn't produce great pictures. Thanks for any feedback! -- Bastien ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Camera saturation - image compression level
Bastien wrote: - shots of the moon are often saturated: how to reduce the gain of the camera? Ideally one would like to do this manually... I never figured out how to control the gain from software. - is there a way to take pictures with a higher resolution? the default compression level doesn't produce great pictures. Yes, sort of. Last year I figured out a way to capture and reconstruct the raw data from the camera using a higher quality demosaicing algorithm. The process is documented here: http://lists.laptop.org/pipermail/devel/2008-February/011029.html --Ben signature.asc Description: OpenPGP digital signature ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Camera saturation - image compression level
I had heard of dcraw (http://www.guillermoluijk.com/tutorial/dcraw/index_en.htm) but never used it except once (not on XO), called from imagemagick as a delegate like this: $ convert dcraw8:image.crw image.png Sean On Thu, Dec 3, 2009 at 3:26 PM, Benjamin M. Schwartz bmsch...@fas.harvard.edu wrote: Bastien wrote: - shots of the moon are often saturated: how to reduce the gain of the camera? Ideally one would like to do this manually... I never figured out how to control the gain from software. - is there a way to take pictures with a higher resolution? the default compression level doesn't produce great pictures. Yes, sort of. Last year I figured out a way to capture and reconstruct the raw data from the camera using a higher quality demosaicing algorithm. The process is documented here: http://lists.laptop.org/pipermail/devel/2008-February/011029.html --Ben ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
