Tonality question

Started 11 months ago | Discussions thread
Anders W
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Re: Was is not a question of tonality?
In reply to Steen Bay, 11 months ago

Steen Bay wrote:

Anders W wrote:

assaft wrote:

Anders W wrote:

PerL wrote:

Anders W wrote:

Sergey_Green wrote:

Anders W wrote:

As demonstrated, neither appears to help.

These graphs are more misused than they are helpful.

So specifically what is wrong with it?

The OP describes his concern as follows:

"To clarify, I am not talking about the short DOF/Bokeh, I mean the exposure dynamic range in the pictures, the tonality (sorry I'm not native english speaker so I can't put it better)."

Hi Anders,

This is OT, but can you give an intuitive explanation where the Tonal Range advantage of the Canon as calculated by DxO, has a visible manifestation in images? I know that higher SNR 18% values are translated into less noise at 'well' exposed parts, and that higher DR values are translated to less noise at deep shadows, but I don't know how to interpret the Tonal Range scores. I found this in the glossary on DxO's site and also this discussion, but I don't have a clear idea of what to expect from a camera with higher Tonal Range values, e.g. when comparing the E-M1 to an improved E-M1 that has a Tonal Range graph higher by, say, 1 bit (the Canon has less than that).

Thanks,

Assaf

Technically, it is what DxO says it is in the glossary (the number of distinguishable shades of gray) where the criterion for distinguishable is that it exceeds the noise level. In the end, tonal range is just another measure of signal-noise performance and is likely to show differences between cameras very similar to those you see if you look at SNR 18%.

The reason why the 5D2 does better than the E-M1 with respect to tonal range as well as SNR 18% (at the same ISO) is that it collects more light at the same exposure (due to the greater sensor area). This gives it the upper hand in the highlights and midtones. The reason why the E-M1 does better than the 5D2 with respect to DR (at lower ISOs) is that it has less read noise. This gives it the upper hand in the shadows, which is generally the weakest part of any image technically speaking. This in turn makes improved shadow rendering particularly welcome (since shortcomings are easily visible).

Another way to put it is to say that the 5D2 has better tonality in the highlights and midtones whereas the E-M1 has better tonaility in the shadows (at lower ISOs).

Maybe it's necessary to define "shadows" here. E-M1 has an advantage if looking 12 stops below full saturation at base ISO, but what if looking e.g. 8 stops below instead? Where is the 'crossing-point'?

Don't know if I feel like doing the math for this particular case. But here's how to do it for those interested.

http://www.dpreview.com/forums/post/41640150

What is clear, as shown by that post, is that the point where photon noise starts becoming more important than read noise moves closer to the clipping point as we crank up the ISO.

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