Posted 19:50 UTC (Wed) by farnz (subscriber, #17727) By working in 16 bits per channel while I'm fixing my mistakes, I get to recover an otherwise lost exposure if I were limited to 8 bpc, the major corrections I need to make will also trash the image. But the fact remains that I didn't manage that: I got an exposure with 12 bits per channel from the sensor of those 12 bits, for most of the image, only the lowest 7 to 9 bits per channel are actually interesting data, except in the area that reflected the setting sun, where it's the top bits that are interesting data. I need to get better at using the tools I have in the field, not just fixing it up later. Now, you can argue that I should have made better use of the camera, and got an exposure where the sunlight reflecting on the metal object is overexposed, but the rest of the exposure is good, and I'd not disagree. It's simple things like catching a reflection of the sun in an otherwise dark composition, resulting in the swan (that then chooses to fly off) being too dark, and the duck in the shade being virtually invisible. If I were working with JPEGs, I'd just have to discard the exposure entirely, no matter that it's the only one where I got the composition right. These are not subtle improvements I'm still not a good enough photographer to get the exposure almost right first time. I'm rescuing bad exposures that wouldn't be usable at all if not retouched from RAW. Posted 12:08 UTC (Wed) by farnz (subscriber, #17727) I'm no expert, so I get a bad exposure of a well-composed scene, and have to play to make it look good (fortunately, my current tool of choice, digiKam, works in 16-bit, and gives me the adjustments I need to fix things).
This is part of why photographers disagree on why it's needed a better photographer would have got a decent exposure in the first place, one that didn't need quite so much fiddling to make it look good. I throw away up to 3 bits improving contrast, making the bits in shadow have just 3 bits of accuracy in the range 0x00 to 0xff. I throw away 2 bits in the shadowy areas, leaving 6. Now do the same process with an 8-bit image. Because I started with 12 bits, my resulting, visually improved image has between 7 and 9 bits of accuracy - when I downconvert to 8-bit for final output, I get 7 to 8 bits of accuracy some people may notice this in the areas that were shadowy, but it's no longer that bad.
If I'm working in 16-bit, I can lighten the bits that were hidden in shadow by a small amount (say the equivalent of 2 bits), and then enhance contrast image-wide, costing me the equivalent of 3 bits of accuracy. The sensor has 12 bits of accuracy, or, put differently, 4 to 5 bits I can throw away when trying to fix my mistakes before putting this photo on the web.
#GIMP GRADIENT LIGHTING SERIES#
Take, for example, a bad photograph taken with inadequate lighting, and shadow on an amateur DSLR like the Canon Rebel series (D550 in my part of the world). Where it becomes important is not when painting afresh, but when editing an image. Posted 9:11 UTC (Wed) by farnz (subscriber, #17727)
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