Canon DSLRs are getting a beating because the DR as a function of ISO measured at DxOMark starts to flatten asymptotically towards 11-12Ev at ISO1600 and below, while recent Nikon DSLRs (and everything based on Sony sensors) appears to improve their DR all the way to ISO 100 (14+ Ev):
http://www.dxomark.com/index.php/Cameras/Compare-Camera-Sensors/Compare-cameras-side-by-side/(appareil1)/795|0/(brand)/Canon/(appareil2)/792|0/(brand2)/Nikon
The difference appears to be Canon using off-sensor ADC (but perhaps on-sensor analog gain). Therefore, a significant amount of noise is added to the signal subsequent to analog amplification and prior to ADC. By raising the amplifier gain "just enough", the signal will be hot enough to travel this path without being affected that much by noise. DSLRs based on Sonys on-sensor ADC are not affected in the same way, and many are described as "ISO-less", i.e. raw shooters might just as well shoot in ISO 100 all the time, under-exposing when necessary and raising the brightness in their raw developer instead of worrying about ISO in camera.
The potential of using "dual ISO" ought to be to have the highlight capability of ISO100, but improving the shadow noise by increasing the gain.
The downside is that ISO cannot be applied as a function of regional signal level: having alternate line(pairs) having different ISO is a kind of "interlacing" that will amplify some sensels that should have been amplified, and not amplify some sensels that should have been.
I think that the image examples shown in this thread have been somewhat misleading in that they appear to compare a regular "flat" image with a tone-mapped dual ISO image. Just like when comparing HDR photography to LDR photography, I think that that is only 50% of the story. In order to really visualize the differences, we might want 4 images:
1. Regular captured, Regular processed image
2. Regular captured, Tonemapped image
3. DualISO captured, Regular processed image
4. DualISO captured, Tonemapped image
For most, the difference between image 2 and image 4 might be most telling, as the tonal range should be similar, but DualISO ought to have less visible shadow noise and some artifacting/loss of resolution.
Is it possible/feasible to pre-process dualISO images into something that appears like regular 7D images (only with less shadow noise) suitable for any raw converter?
-h
