Pixel Count Issue
ofwolf42 wrote on Feb 02, 2011
I have a series of FITS images that were taken (originally as jpeg images or movies) with a webcam. When I view them in DS9, there seems to be a max pixel count of 255. This has taken an amount of detail away from the image. I was wondering what would cause this limit on the pixel count.
I've tried different software but they all seem to have this issue. I'm wondering if it is the hardware but I'm told this is unlikely. This only leaves the conversion process. I'm using ubuntu's "convert" command to convert the jpegs to fits.
Has anyone come across this problem or has anyone any ideas for a solution?
I've tried different software but they all seem to have this issue. I'm wondering if it is the hardware but I'm told this is unlikely. This only leaves the conversion process. I'm using ubuntu's "convert" command to convert the jpegs to fits.
Has anyone come across this problem or has anyone any ideas for a solution?
Mike Fitzpatrick wrote on Feb 02, 2011
JPEG images have 8-bit pixels (plus a colormap), even when done as e.g. a 24-bit JPEG that only means there are 8-bits per RGB channel, not 24-bits of dynamic range. When converted to FITS the colormap is applied and the pixels are essentially then the colormap indices, in the case of 24-bit RGB they become the 8-bit (i.e. values 0-255) grayscale value. You can scale the actual values, but the data will only ever have 256 levels.
ofwolf42 wrote on Feb 02, 2011
Well that's unfortunate. Is there any available software capable of directly recording to FITS? I remember looking for such software but didn't find any for general webcam use. Only for specific hardware.
Mike Fitzpatrick wrote on Feb 02, 2011
I suspect the real problem is that your webcam is only capable of 8-bit captures, not the format that gets written. In either case, Google is your friend to find the answer.
ofwolf42 wrote on Feb 02, 2011
Thank you very much for your help, fitz.
Last post on Feb 02, 2011