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#1
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White balance
Is white balance information used to determine the way a (raw) image is
displayed, or is it used to cause the sensor to record the information differently in the first place? Daniele |
#2
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White balance
Is white balance information used to determine the way a (raw) image is displayed, or is it used to cause the sensor to record the information differently in the first place? Daniele If you shot in RAW you can forget the White Balance - You can set it later in your RAW converter DAVE Bristol UK http://djmp.co.uk/slr/ |
#3
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White balance
D.M. Procida wrote:
Is white balance information used to determine the way a (raw) image is displayed, or is it used to cause the sensor to record the information differently in the first place? I believe it actually changes the data in the analog to digital conversion but it's not usually all that big of a deal to adjust with the raw converter. In other words, it rarely matters. I could be wrong. People talk about using filters for slight improvements, and there was a fuss over being able to read the as-shot WB in the Nikon D2x when it came out in non-nikon raw converters, presumably that all had to do with getting the optimum image quality by knowing the actual WB used for the file. -- Paul Furman Photography http://edgehill.net Bay Natives Nursery http://www.baynatives.com |
#4
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White balance
Paul Furman wrote:
D.M. Procida wrote: Is white balance information used to determine the way a (raw) image is displayed, or is it used to cause the sensor to record the information differently in the first place? I believe it actually changes the data in the analog to digital conversion but it's not usually all that big of a deal to adjust with the raw converter. In other words, it rarely matters. I could be wrong. People talk about using filters for slight improvements, and there was a fuss over being able to read the as-shot WB in the Nikon D2x when it came out in non-nikon raw converters, presumably that all had to do with getting the optimum image quality by knowing the actual WB used for the file. I just did a test and there is only a very very slight change in the histograms when I shoot and adjust to the far extremes of kelvin temp in camera and the raw converter. It's not identical but close enough for practical purposes. That's on a tripod in manual mode. -- Paul Furman Photography http://edgehill.net Bay Natives Nursery http://www.baynatives.com |
#5
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White balance
Dave wrote:
Is white balance information used to determine the way a (raw) image is displayed, or is it used to cause the sensor to record the information differently in the first place? If you shot in RAW you can forget the White Balance - You can set it later in your RAW converter But what as a reference? It might be easy to do it if your image has a handy white wall or something to take a measurement from, but not all images do? And just to be clear: are you saying that a raw image shot with wildly incorrect white balance, and one shot with perfect white balance, actually contain the same data apart from the white balance information? Daniele |
#6
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White balance
D.M. Procida wrote:
Dave wrote: Is white balance information used to determine the way a (raw) image is displayed, or is it used to cause the sensor to record the information differently in the first place? If you shot in RAW you can forget the White Balance - You can set it later in your RAW converter But what as a reference? It might be easy to do it if your image has a handy white wall or something to take a measurement from, but not all images do? That can be a problem. E.g. a red sunset. In such cases, a calibrated monitor and remembering the colors is about your best hope. And just to be clear: are you saying that a raw image shot with wildly incorrect white balance, and one shot with perfect white balance, actually contain the same data apart from the white balance information? Raw, at least in some cameras is a straight linear analog to digital conversion with no changes to the data regardless of settings on the camera. Some cameras then do post processing before writing the raw to the memory card (Nikons, for example do some minimal processing including lossy compression via a look-up table, although in practice this processing is negligible except in rare cases). Canon's raw appears to be a true raw, for example. Roger |
#7
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White balance
Roger N. Clark (change username to rnclark) wrote:
And just to be clear: are you saying that a raw image shot with wildly incorrect white balance, and one shot with perfect white balance, actually contain the same data apart from the white balance information? Raw, at least in some cameras is a straight linear analog to digital conversion with no changes to the data regardless of settings on the camera. OK, but it is at least theoretically possible - is it not? - that a camera could use its white balance settings to affect the way the sensor records the light (as I understand it does with sensitivity settings in order to get it to behave differently). Daniele |
#8
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White balance
In article , change username to rnclark
wrote: Some cameras then do post processing before writing the raw to the memory card (Nikons, for example do some minimal processing including lossy compression via a look-up table, although in practice this processing is negligible except in rare cases). Canon's raw appears to be a true raw, for example. nikon has both an uncompressed and compressed raw. lower end nikon cameras only offer the compressed variety, while higher end ones offer both. |
#10
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White balance
On Sep 3, 12:47 am, (Floyd L. Davidson) wrote:
(D.M. Procida) wrote: Roger N. Clark (change username to rnclark) wrote: And just to be clear: are you saying that a raw image shot with wildly incorrect white balance, and one shot with perfect white balance, actually contain the same data apart from the white balance information? Raw, at least in some cameras is a straight linear analog to digital conversion with no changes to the data regardless of settings on the camera. OK, but it is at least theoretically possible - is it not? - that a camera could use its white balance settings to affect the way the sensor records the light (as I understand it does with sensitivity settings in order to get it to behave differently). In fact that does happen. Exposure calculations, histograms, and blink-on-over-exposure LCD displays will all change depending on the WB, because WB is applied to the JPEG image produced and it is _that_ image, not the raw sensor data, which is used to generate those particular data sets. (That is true even if you shoot RAW only.) Also it appears that some cameras might (the manufacturers are tight lipped about sensors and digital to analog converters, so we don't really know) actually have some analog gain adjustment done, based on WB sensing, in the analog channel between the sensor and the conversion to digital. In fact, the external WB sensor of the D2x makes me suspect that they planned to make the camera WB the data before digitisation (since then you'd need to know WB before you did anything to the data!). Also Nikon seems to imply that something is done to the data in the analogue domain (for both the D2x and d200), but they don't say what. And the D200, at least, certainly doesn't WB the data. However, if you use the multiple exposure function of the D200, WB is applied to the raw data. It's a neat function, by the way, you can set the camera to take a multiple exposure of 10 frames at ISO 100 and the result is silky smooth. You cannot see noise no matter how much you lift the shadows and sharpen. It's like having very low ISOs available. But you have to set WB accurately (I suspect they apply other adjustments too, such as contrast etc, but I'm not sure). |
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