DxOMark's measured ISOs vs. manufacturer ISOs

Started Mar 13, 2013 | Discussions thread
Jack Hogan Veteran Member • Posts: 6,982
Re: DxOMark's measured ISOs vs. manufacturer ISOs

GordonBGood wrote:

Let's assume that the light illumination was exactly the same and see where that takes us:

  1. I use the ISO 3200 results...

In summary, the differing exposures of the cameras means very little to the raw image quality/noise comparisons when both have been post processed to about the same output brightness levels other than if the required exposures started to get down to a tenth of a second or slower where differing amount of hot pixels would start to make a difference.

Hi GB,

I think the point is that, to stay within the boundaries of this thread, it is misleading to compare sensors at the same in-camera ISO setting. For instance if a hapless potential buyer were to compare the two images mentioned above in supposedly 'similar' conditions, the EM5 looks leaps and bounds better than the G3 in terms of noise performance. Incredible, wow, bravo Olympus!

Noise Performance at the same in-camera ISO settings of 3200

Convinced after such an authoritative comparison our hapless buyer goes out and gets an EM5. He is however disappointed to find out that, in the same field conditions, its noise performance is not really significantly better than his friend's much cheaper G3. How is this possible, DPR's comparison showed that at the same in-camera ISO his EM5 should blow the G3 out of the water!?!

Ah, but in-camera ISOs mean nothing these days of REI. Might as well give them a name: 1/2, base, 2x, 4x etc. To compare apples-to-apples the performance of two sensors (the basis of camera set IQ), one first needs to set them up so that they respond similarly to light. That's easy because DSC sensors being linear, one only needs to make sure that they clip at the same Exposure and ETTR. Luckily, DxO measures saturation exposure of every sensor for us. So our hapless EM5 owner, having evaluated his scene, sets ISO in both cameras up so that their sensors will both saturate at the same Hsat = 0.0525 lx-s, which just so happens to correspond to an in-camera setting of ISO 3200 for the EM5 and ISO 1600 for the G3 (or Ssat of 1489 and 1481 respectively). And this is the response he gets:

Noise performance when in-camera ISO is chosen so that both *sensors/ADCs* will provide the same mean outputl when presented with the same Exposure

Whoa, un-wow, right? The G3 is not so bad after all, in fact*... How dumb was he to compare cameras on the basis of in-camera ISO settings! If he had known he may well have chosen otherwise. He wonders whether the marketing folks at Olympus had anything to do with the ISO labelling and why the competent folks at DPR did not warn him about that, but with his new little jewel in his hands he soon forgets about the whole affair and goes out to take some outstanding pictures .-)

Again, the secondary conclusion is that much too much concern is being made about this and much more than it deserves.

Indeed, especially if one understands the above.

*All right, all right - so the lighting or the reflected meter constant k is slightly different between the two, resulting in shutter speeds 1/3 of a stop apart, but you get my point.

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