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Interesting paper on noise, DR, etc. - link to Univ. Of Chicago


zml

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Interesting to see the table there with the light collecting efficiency per unit area of

various sensors - on the Canon side there was a big jump between the 10D and 20D

but not much improvement (after allowing for the 1/3 stop difference in true vs

indicated ISO) since - claims about "improved microlenses" etc notwithstanding! Bears

out what is I think common wisdom on these forums that image quality improvements

since the 20D have been incremental at best, but still good to see it stated more

quantitatively.

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Here are some quotes I found interesting....

 

1. モOn the other hand, if shooting raw, it makes little sense to use the extended ISO's since they are simply mathematical manipulations of the raw data post-capture, and their main effect is to throw away one or more stops of highlight headroom as the doubling, quadrupling etc of the raw values pushes more and more of them beyond the maximum recordable value of 4095 for 12-bit, or 16383 for 14-bit data. Setting the highest analog ISO amplification keeps the headroom, and one can always do as much additional software amplification as is needed afterward during raw conversion.ヤ

 

2. モOne sees in particular that the 1D3 and 5D have comparable high ISO performance at the pixel level, with the 1Ds3 trailing by about half a stop; and at low ISO, the 1D3 leads, followed by the 1Ds3 and then the 5D.ヤ

 

3. モLower end Canon models do not perform analog amplification for the intermediate ISO's, rather the intermediate ISO's are implemented by a multiplication of the raw data in software after quantization, and there is only a single stage amplification in hardware; strictly speaking, they do not have intermediate ISO amplification.ヤ

 

>>>I think most or us knew this, however did not know what models.<<<

 

4. モBoth Canon and Nikon have introduced a finer level quantization of the sensor signal in digitizing and recording the raw data, passing from 12-bit tonal gradation in older models to 14-bit tonal depth in newer models. A priori, one might expect this transition to bring an improvement in image quality -- after all, doesn't 14-bit data have over four times the levels (16384) compared to 12-bit data (4096)? It would seem obvious that 14-bit tonal depth would allow for smoother tonal transitions, and perhaps less possibility of posterization. Well, those expectations are unmet, and the culprit is noise.ヤ

モCuriously, all the 14-bit cameras on the market (as of this writing) do not merit 14-bit recording. The noise is more than four levels in 14-bit units on all of these cameras (Nikon D3/D300, Canon 1D3/1Ds3 and 40D); the additional two bits are randomly fluctuating, since the levels are randomly fluctuating by +/- four levels or more. Twelve bits are perfectly adequate to record the image data without any loss of image quality, for any of these cameras.ヤ

 

 

Jason

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I shoot a lot of low light theater and high ISO noise performance is very important to me. I regularly shoot at ISO 3200 or 6400 with my Canon 1DmkIII. I shoot RAW files mainly to tweak white balance and to adjust exposure.

 

For someone who shoots frequently at the limit of their camera's sensitivity, is there any lesson to be learned from the article? I gather that I could get better results by shooting at ISO3200 and underexposing one stop. Pushing the developing on the computer is the same as what the camera is doing, but I could selectively do it in ACR and Lightroom whereas at ISO6400 the camera is pushing the entire image.

 

It's not the noise at ISO6400 that bothers me so much as it is the loss of detail. I think that a little experimentation is in order...

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