In this thread:
http://luminous-landscape.com/forum/index....showtopic=24375 Panopeeper showed how expanded ISOs do not correspond to real electronic ISO gains.
I thought however that intermediate ISO values (like ISO640) were also fake coming from software adjustment over a real ISO400 (or maybe ISO800) shot.
But I have been given 4 RAW files of the Nikon D300 and calculated its histograms:
14 bit / ISO400
14 bit / ISO640
12 bit / ISO400
12 bit / ISO640
I was surprised to see that ISO640 RAW histograms (i.e. only non-interpolated RAW data, just scaled from 12/14 to 16 bits without any additional WB scaling, saturation scaling of offset substraction) look the same as ISO400, so I don't have any evidence to suspect ISO640 is a fake when compared to ISO400:
[span style=\'font-size:14pt;line-height:100%\']14 bits[/span]
ISO400ISO640[span style=\'font-size:14pt;line-height:100%\']12 bits[/span]
ISO400ISO640In addition to finding no differences between ISO400 and ISO640, one can see that:
- In 14 bits, R and B channels have holes in the RAW data. Could this slight expansion be related to some WB in-camera adjustment? or just and adjustment to reach the saturation level? if so, why G channel is not corrected the same way?
- In 12 bits, again G channel looks soft, but R and B channels seem to suffer of some periodic level aggregation. Any explanation for this?
The RAW files are available here for download:
14 bits/ISO400 RAW14 bits/ISO640 RAW12 bits/ISO400 RAW12 bits/ISO640 RAW