DxOMark's measured ISOs vs. manufacturer ISOs

Started Mar 13, 2013 | Discussions thread
texinwien Veteran Member • Posts: 3,326
Re: DxOMark's measured ISOs vs. manufacturer ISOs

Jack Hogan wrote:

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.

It's not.

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!

This is one reasonable way to compare noise between two cameras, by taking pictures of the same test scene, ensuring that both get the same exposure, using matching camera ISO settings (aka exposure indices).

.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.

Excellent choice.

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.

No, he doesn't.

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!?!

And it does, or, at least, it matches DPReview's studio tests closely.

Ah, but in-camera ISOs mean nothing these days of REI.

As DPReview has stated, SOS is what they, the camera manufacturers and you should be paying attention to.

one first needs to set them up so that they respond similarly to light.

Please define '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 where you're going off the tracks. Either he chooses to compare based on camera ISO with the caveats I listed above, or else he chooses to compare on the basis of saturation sensitivity, in which case he will dial in +1EV of exposure compensation on the E-M5, knowing that the cameras meter based on their ISO settings, and that if he wishes to compare on any other basis, he will have to make the appropriate adjustments to ensure that both sensors get the same exposure, just as in the first test.

Note - when he dials in the extra stop of exposure comp on the E-M5, the shutter speed will closely match that of the G3, assuming equal scene illuminance and aperture settings on the two cameras - or buyer pays no penalty here of any sort.

And this is the response he gets:

Of course, this is not the response he gets, because this response is comparing based on saturation sensitivity while relying on ISO setting-based metering, clearly a mistake in logic that our intelligent buyer will avoid.

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?

Only if he was too confused to understand that he needs to set the correct exposure if he wishes to compare on the basis of anything other than the cameras' ISO settings.

How dumb was he to compare cameras on the basis of in-camera ISO settings!

Not dumb at all. The buyer, being rather intelligent knows that comparing based on camera ISO settings is one valid way to compare.

Indeed, especially if one understands the above.

If the buyer doesn't understand saturation sensitivity, he will shoot using the camera's ISO settings and get results that closely match those shown in DPReview's tests.

If the buyer does understand saturation sensitivity, he will know that he has the option to ignore the camera's ISO setting and shoot based on its saturation sensitivity, realizing, of course, that he will be responsible for making proper exposure compensation adjustments. In this case, he will enjoy results that closely mirror DxOLabs' saturation sensitivity-based measurements.

If he's confused? Well, if he's confused, he might think he can test based on saturation sensitivity while letting the camera choose exposure values that are based on its ISO setting, in which case he will probably be disappointed with the results of his tests. Not understanding what's going wrong, he'll make some misguided comments about marketing-based conspiracies, return the E-M5 and hopefully stick to a point-and-shoot, since he's obviously not to be trusted with anything more complex

*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.

The point, jack, is that you're being the confused buyer in the above examples. Hope it's clear to you now. Don't be that guy.


 texinwien's gear list:texinwien's gear list
Panasonic Lumix DMC-GM5 Olympus E-M5 II Olympus 12-40mm F2.8 Pro OnePlus One Canon EOS 300D +20 more
Post (hide subjects) Posted by
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow