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Index of Subjects Hans: Agreed -- I actually looked at your colour picture last night and thought the same thing (great picture as always by the way, as others have said). Another potential 'enemy', though, is non-linear processing. I don't know if consumer digital cameras use a non-linear algorithm to compress a scene's extended brightness scale from the CCD chip into the 256 steps usually available in the conversion from light energy to pixel memory record. I became concerned about this when taking pics of fluorescence down a microscope, and had to go to some length to check that the fancy camera/software there was giving a linear output up to CCD saturation, so we could make proper relative brightness estimates from the images. Don't know the answer for consumer cameras. In addition, some of Photoshop's filters must act non-linearly to distort the initially recorded image, for instance the wonderful Unsharp Mask: wondered if you may have used it on the colour picture of the rainbow (the telephone cables have unexpectedly bright white adjacent dots). Another perhaps curious feature is that the few clouds seem quite bright when present just below and extending into your primary rainbow, but wash out where they look to extend beyond into Alexander's (putatively dark) band. But that could just be in the cloud distribution itself, not in the processing. It would be interesting to know if you or anyone on the list knows whether consumer cameras (or some of them) operate linearly, that is (roughly), give out twice the number (0-256) to the memory pixel record where the scene is twice as bright objectively (not visually). Or do some/all use intensity compression to render scenes more acceptable or manageable? Steve ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Quoting Hans Toom <htoom@hfx.eastlink.ca>: > When analyzing photographs colour can sometimes be our enemy so I've > desaturated the first rainbow photo to black and white. The visible > brightness of the image is clearly brightest below or within the > primary rainbow and darkest between rainbows and the sky above the > outer rainbow. The visible brightness in the space between rainbows > and the background sky above the rainbows appears to my naked eye as > identical. No dark band is visible to my eyes anywhere. > > The overall effect of the desaturated image is much like a giant > eyeball with the space from the inner rainbow skyward becoming the > imaginary eyelid. The visible brightness below the lower rainbow is > stunning and much brighter than the background sky as seen above the > outer rainbow. > > http://www.hanstoom.com/StockPhotos/Visions3/0179.html > > Hans Toom > Portuguese Cove, Nova Scotia, Canada > http://www.hanstoom.com/ >
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