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Problems with raw images produced by sx40 with chdk.

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Problems with raw images produced by sx40 with chdk.
« on: 08 / February / 2013, 19:37:15 »
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took some images of some desktop items at 24mm setting,one foot from desktop items  at f8.0 etc. in jpeg  and Raw dng.   The jpeg image came out fine.  But the raw images on each corner have circular black areas(vignettes) which i presume is the lens?  Why is this happening  and how can this be corrected.  Also i shot the images at f 8.0,but when downloaded the jpeg image showed shot at f8, but the raw images taken  showed taken at f 7.5. Why the differential?   All six of the raw images although shot at different shutter speeds showed shot at f7.5?  Attached are the two images.

Re: Problems with raw images produced by sx40 with chdk.
« Reply #1 on: 08 / February / 2013, 19:41:53 »
The jpeg image came out fine.  But the raw images on each corner have circular black areas(vignettes) which i presume is the lens?  Why is this happening  and how can this be corrected. 
Welcome to CHDK RAW - where you get EXACTLY what the camera sensor sees.  No post processing, no lens correction, no white balance, nothing but raw pixels!

You probably want to spend a little time reading up on this so here's the links :

link> CHDK Wiki Page about RAW
link> CHDK Forum thread on RAW
link> CHDK Wiki Page about Raw Software
link> CHDK Forum Board for RAW
link> How do you fix lens distortion with CHDK RAW files?
link> Decoding CHDK RAW images from a new cameras
link> rawconvert utility to allow manipulation of CHDK RAW files
link> DNG4PS-2 utility to convert CHDK RAW images to DNG format
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