phill.butte wrote:...the real problem was a variation in sensitivity of the camera sensor of about 5% starting at the upper left corner and going to the bottom middle. There was also about a dozen or so spots about 20 pixels in diameter with a 4-5% variation.
Canon wrote:Lens correction
The most interesting addition to the latest version of DPP is the lens aberration correction function. Although all Canon lenses are designed and manufactured to produce the highest quality images, constrains of technology, manufacturing and cost mean that some minimal aberrations still exist in the lenses. This new addition to DPP aims to correct these minor aberrations and so produce even higher quality images. The adjustments available correct four factors in the images:
Otherwise known as corner-shading or vignetting. Digital cameras are very susceptible to light not striking the sensor at the correct angle, and with some lenses it is possible to see a slight fall-off in the corners of the image where it looks darker than the rest of the frame. This adjustment aims to even out the lighting across the frame.
With wide-angle lenses, it is possible to see distortion around the edge of the lens â€“ straight lines become curved, and subjects at the edge of the frame are distorted. This adjustment ensures straight lines are straight.
Around the edges of an image it is occasionally possible to see colour fringing, especially at high contrast edges such as branches of a tree against the sky. This adjustment will effectively remove the chromatic aberration.
At the edge of very bright areas, it is occasionally possible to see red or blue colour blurring. This adjustment will remove the colour blurring. To make these adjustments, the software has to re-process the image. When doing this, it makes use of information that is stored with the image when you capture a RAW file with an EOS camera as well as a database of information included with DPP. It makes use of four pieces of information:
1. Lens optical data â€“ This is included with DPP and is like a fingerprint for each lens showing the optical characteristics of that lens.
2. Lens ID â€“ Lens information for the lens used. This is stored automatically by the camera.
3. Lens focal length â€“ The exact focal length that was used to capture the image. This is stored automatically by the camera.
4. Distance information â€“ The focal distance used when the shot was captured. This is stored automatically by the camera.
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