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#1
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How does digital process white balance?
Most digital cams have the ability to set the WB for sun, tungsten,
etc. What actually happens in the camera when you set tungsten, for example? Is the blue channel amplified or reds/greens cut back? Combination of the two? |
#2
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How does digital process white balance?
In article . com,
"phk" wrote: Most digital cams have the ability to set the WB for sun, tungsten, etc. What actually happens in the camera when you set tungsten, for example? Is the blue channel amplified or reds/greens cut back? Combination of the two? Exactly. And the reason it's better to do this in the camera than try to fix it later is that the camera's sensor returns typically 12 bits per colour (i.e. 4096 levels) and this is reduced to 8 bits per colour (256 levels) in the JPG that is saved to tthe card. SO there is quite a bit of scope for adjusting the level of any one channel by up to a factor of 16 wthout causing a decrease in image quality. Or, you can save the raw data and do it later in Photoshop or your camera's software. In which case the camera's white balance and saturation and sharpening and so forth settings are ignored. -- Bruce | 41.1670S | \ spoken | -+- Hoult | 174.8263E | /\ here. | ----------O---------- |
#3
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How does digital process white balance?
Thanks for the explanation. Would anything be gained by using a color
filter? |
#4
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How does digital process white balance?
No...not really. You are as likely to make it worse as better. If storage is
the issue then shoot JPG and find out which situations where your camera can be trusted....unless its tricky lighting then use RAW and fix it later. -- Thanks, Gene Palmiter (visit my photo gallery at http://palmiter.dotphoto.com) freebridge design group "phk" wrote in message oups.com... Thanks for the explanation. Would anything be gained by using a color filter? |
#5
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How does digital process white balance?
"phk" wrote in message oups.com... Thanks for the explanation. Would anything be gained by using a color filter? Yes, assuming it is matched to the sensel (with Bayer CFA) sensitivity. You'd ideally optimize (maximize without introducing clipping) channel exposure, or at least prevent the need to boost a channel's signal in post-processing. Boosting in 'post' increases noise and quantization errors. There may be a need to create a special camera profile for accurate color. Whether the effort is worth it, depends on the specifics of the situation. When cameras start to adjust the analog gain based on white balance, the differences will become smaller. In general, I'd recommend using color conversion filters (e.g. 80A or 80B) when e.g. shooting in tungsten light, because it reduces the noise in the blue channel, although it will increase overall exposure time with some 2 stops. Bart |
#6
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How does digital process white balance?
Bart van der Wolf wrote:
In general, I'd recommend using color conversion filters (e.g. 80A or 80B) when e.g. shooting in tungsten light, because it reduces the noise in the blue channel, although it will increase overall exposure time with some 2 stops. ....and if you increase your ISO to compensate for these 2 stops you'll increase noise in ALL the channels. BugBear |
#7
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How does digital process white balance?
"bugbear" wrote in message ... Bart van der Wolf wrote: In general, I'd recommend using color conversion filters (e.g. 80A or 80B) when e.g. shooting in tungsten light, because it reduces the noise in the blue channel, although it will increase overall exposure time with some 2 stops. ...and if you increase your ISO to compensate for these 2 stops you'll increase noise in ALL the channels. No need to increase ISO, just expose longer... If camera shake becomes an issue, then by all means choose between turning up analog gain (ISO) or under-exposing the blue and green channels. Turning up ISO should give better results than postprocessing to compensate underexposure. Bart |
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