D4 vs 1Dx (Imaging Resource), RAW, ACR, 6400-12800

Started Sep 4, 2012 | Discussions thread
dosdan Contributing Member • Posts: 510
Re: D4 vs 1Dx (Imaging Resource), RAW, ACR, 6400-12800

bobn2 wrote:

It's not a 'cheat' - it's DxO getting confused about what ISO is.

No just ISO. DxO's use of of "exposure" is confusing too.


ISO : "RAW (DxO Measured) ISO" vs "JPEG ISO".

Exposure :
Taking a digital image involves two distinct phases:

CAPTURING. Sensor captures photons and converts the charge to an analogue voltage signal.

RENDERING. Voltage may have analog gain applied before ADC, may have digital gain applied in/after ADC, or may have no extra gain applied at all. ADC converts analogue voltage to a digital signal. May have non-defeatible NR applied before demosaicing. Demosaicing. WB, TRC and colourspace conversions applied. May have adjustable NR, black-level, resizing, sharpness, contrast, hot or stuck pixel reduction applied. Saved in either a raw or other image file format (e.g. JPEG) with either lossless or lossey compression, or uncompressed.

I think the term "exposure" should only be applied to the Capture phase, but look at these quotes from DxO (my bolding):

ISO sensitivity relates to exposure

the elements that determine the exposure in the final picture .
A first key factor is the sensor exposure [ that what I think is exposure ]


There is a last parameter that is almost orthogonal to the ones above and which allows the photographer to obtain a good exposure: ISO sensitivity. [ Surely this is not capturing, but rendering? ]


still possible to obtain a well-exposed picture by playing with the ISO setting


For a given scene illumination (measured by a luxmeter), there are a number of combinations of exposure times, lens apertures, and ISO settings that lead to the same exposure .


ISO sensitivity on the RAW image has exactly the same qualitative meaning as explained above. However, the user can usually access the image only after the RAW conversion and a subsequent exposure change . So the RAW ISO value may differ from the ISO on the camera from a user’s point of view

So it looks like DxO considers the Rendering phase to be part of the "exposure process", as opposed to just the Capturing phase.


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