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denoir
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Re: Sony NEX-C3 first impressions


Ajay C wrote:
No CFA by itself will not cause color shift. Different hues are common. There is math to it but I\'ll try to explain in simple terms. For instance, take a pixel quad (2x2 - [Green, Red] and [Blue, Green] in the next row), and imagine white light rays coming in perfectly normal. CFA filters the light, and the corresponding pixels get excited, and produce an electrical response. i.e. all channels respond the same way and when pixel data is demosaiced, it is a perfect white response (assuming white balancing was done). Now imagine, light rays coming in at an oblique angle and the micro-lenses dead center on top of the pixel. All of a sudden, all the light that should be gathered by the pixels is - a. not going into the pixel (attenuated), b. some of it reflected around and goes into other neighboring pixels. If you read (a) and (b) carefully, the pixel response has changed and also the neighboring pixels are responding differently. Depending on the angle (and the side) at which light rays hit the pixel, different intensity of light can leak into neighboring pixels, and hence elicit different response. When this neighboring pixel data is used for further processing, and the same color gains (white balancing) are applied, it is not pure white but colored, and depends on which pixel (or a combination) had the best response to these light rays. The key to asymmetrical color shifts is the angle of the light rays itself. Hence the idea behind the shifted micro lenses is to reduce this \"mischanneling\" of the light at the edges of the optical array.


Thanks Ajay, but I still don\'t see how a global left/right asymmetry could arise. The angle hitting a microlens/photosite/pixel on the extreme left side will be exactly the same as one symmetrically on the extreme right side. So why is there a red hue on the left side and cyan hue on the right side?



Jul 28, 2011 at 10:40 AM





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