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Reading an article about the Fuji X100s, I came across this quote:

[...] the high ISO setting is only available when shooting in Jpeg Fine format. When shooting in Raw the highest ISO setting is 6400.

The camera has a rated highest ISO of 25600, so I was wondering why ISO settings greater than 6400 are available only as JPEG. Are the 25600 ISO JPEG photos only the result of the internal processing of 6400 ISO photos?

I like the Fuji X100s very much and it would have already landed into my shopping cart could I afford it :-)

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    Guessing: it may be because the extra ISO is obtained by compressing the dynamic range, thus RAW format doesn't actually gain anything by pushing further. – clabacchio Mar 14 '14 at 13:44
  • @clabacchio I understand. The question is if the extra ISO is obtained by mechanical means or post-processing software. That is, can I get the same result in this camera from an ISO 6400 RAW image after post-processing? – Alberto Mar 17 '14 at 9:32
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This is a classic among Fuji cameras. The standard ISO range is available in both RAW and JPEG but expanded options are only available as JPEG. This is true at both ends of the range. The X100S has Low (100) and High (12800, 25600) ISO settings which are JPEG-only.

These ISOs are probably simulated by simply multiplying the signal in the camera's software which causes 1 or 2 bits per component to be unused. You could argue this still gives you more granularity than JPEG images but the gap is definitely narrowing.

  • "These ISOs are probably simulated." This is also what I'm afraid of, meaning that only up to ISO 6400 is 'real ISO' and above that, only a convenience time saver feature. – Alberto Mar 17 '14 at 8:39
  • Well. Sensors have a native ISO which is 200 for the X100S. Other ISO in the standard range a produced by lowering the saturation point read-out converts voltage into a digital value. With simulated ISO, the value is read at the closest standard ISO multiplied digitally. This is very common and most cameras not using Sony sensors do this for intermediate ISO settings too. – Itai Mar 17 '14 at 13:35
  • So in terms of image quality, there would be no improvements between the ISO 6400 RAW and the ISO 25600 Fine Jpeg, right? In other words, shooting in 25600 is actually worse because jpeg drops some image information? – Alberto Mar 17 '14 at 16:01
  • Remember RAW files are not images. With ISO 6400 RAW data you can probably produce an image of quality similar to that of an ISO 25600 JPEG out of the camera even after pushing it 2 EV which makes things brighter but amplifies noise and is particularly visible in shadow areas. – Itai Mar 17 '14 at 16:20
  • Thanks "With ISO 6400 RAW data you can probably produce an image of quality similar to that of an ISO 25600 JPEG out of the camera even after pushing it 2 EV." This is exactly my question: does the camera do anything more than pushing the image 2 EV and applying noise reduction? Does the camera, for example, apply a higher voltage to the sensor when acquiring the image? – Alberto Mar 18 '14 at 17:12

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