Sony A900 noise, dynamic range and noise reduction

[Guillermo Luijk]

There is more to it. This particular method of noise reduction reduces the average pixel values close to black, and that causes the appearance of higher dynamic range:

What f-stop referred to saturation are we talking about here? Did you manage to quantify the shift in EV of the average signal value with respect to the expected value because of the NR? this can be calculated for ISO1600 (NR OFF vs others). Few levels in the deep shadows mean an important amount in EV.

The guy, who created this review does not understand his own graphs

lol

[Panopeeper]

What f-stop referred to saturation are we talking about here?

I have no idea, nor do I understand what bearing that has on the subject.

Did you manage to quantify the shift in EV of the average signal value with respect to the expected value because of the NR? this can be calculated for ISO1600 (NR OFF vs others)

I do not make such cross-calculations, for they are based on unproven assumptions. I asked Erik to make parallel shots with a Canon camera to croos-check the exposure; if he is making some, I will be able to calculate the differences.

Few levels in the deep shadows mean an important amount in EV

Yes, that's the issue. Changing the average by two levels, later on even by one level can "add" a stop to the DR. Of course, this is all imaginary DR. This has nothing to do with Sony's trick; some cameras have relative clean "base noise", like the old 5D, simply due to the lack of levels. I always felt the 5D is far overrated; you don't see much noise between 0 and 1, do you?

[Guillermo Luijk]

I have no idea, nor do I understand what bearing that has on the subject.

If the exposure shift is only noticeable from let's say -10EV, we wouldn't care at all. Noise make pixels jump by more than 1 f-stop in such dark areas. If exposure shift is happening in -7EV for example, that's a different story and would definitively make DR measures wrong with a conservative SNR=12dB criteria.

I always felt the 5D is far overrated; you don't see much noise between 0 and 1, do you?

I think the 5D is a very good camera for steady shooting, working only in the higher f-stops through multiexposure. If I found one now at 1000€ I would go for it, but it has become impossible to find old stocks. I am a bit scared of the 20Mpx of the new model.
Its good behaviour at high ISOs made people generally consider it a low noise winner. But for tripod high DR applications, were noise in the deep shadows matters, the 5D was just an average camera. I don't think the lack of levels was really the problem, it was simply quite noisy.

[Ray]

Dynamic range through NR reduction (i.e. through detail loss) is not real DR. If you think it is, then I will give you a secret recipe to maximize your DR: apply to all your pictures a gaussian blur filter with 20 pixels radius. All noise will disappear at any ISO so your DR will be stunning. But please don't complain about loss of detail because that kind of DR is what you wanted.

BR

Guillermo,
That's true, and this is where Quentin's method of visual comparison of real-world images can be effective, provided identical scenes are used under the same lighting conditions. If Camera A produces noisier but more detailed shadows than Camera B, then this fact should be apparent in real-world images. If it isn't, then the fact that Camera A is noisier but more detailed, is of no consequence, although it may be of academic interest to some and it may well be essential information for those who are producing their own RAW converter or noise reduction program.

I'm reminded here of Jonathan Wienke's DR test target (downsized version below) which I downloaded over a year ago, took a few shots comparing the DR of my 20D and 5D, then spent hours arguing about the necessity of comparing DR at the pixel level as opposed to the scene level. My view was, and still is, that DR at the scene level is what's important to me, although pixel DR is of some academic interest.

For example, I find it interesting that, according to DXOmark tests, the SNR and DR of the 5D MkII and 20D are approximately the same, at the pixel level. In fact, the 5D2 is sometimes very slightly better in DR by amounts of approximately 1/4 EV, which are not significant in my view. What is significant is the substantially better SNR and DR of the 5D2 in normalised prints, or same size and same FoV images on monitor.

The pixel size of the 5D2 is very close to the pixel size of the 20D. It's interesting that, after a number of years of development between the release of the 20D and the 5D2, so little progress has been made in improving the SNR and DR of the pixel. I would deduce from the DXOmark results that any image taken with the 5D2 that was cropped to the same FoV one would get if one had used a 20D with the same lens, would be of approximately equal quality to the 20D shot. Whether or not this is true can also be determined by visual inspection of real-world images.

[attachment=12482:Jonathan...t_target.jpg]

[Guillermo Luijk]

That's true, and this is where Quentin's method of visual comparison of real-world images can be effective, provided identical scenes are used under the same lighting conditions.

I completely agree. The point is that Quentin didn't state he did any comparision camera to camera. He was just happy with the DR results of his A900 without comparing them to any other machine tested under the same scene. That's why I said he could be just enjoying an imaginary DR (I like this term Gabor introduced) which actually consisted in NR with detail being destroyed in the shadows.

[Plekto]

It's interesting that, after a number of years of development between the release of the 20D and the 5D2, so little progress has been made in improving the SNR and DR of the pixel.

I suspect that this is a built-in limitation with the Bayer pattern itself.  Beyond a certain point, you will need different technology, because software and chips can only do so much to clean it up.

[Panopeeper]

What f-stop referred to saturation are we talking about here?

If the exposure shift is only noticeable from let's say -10EV, we wouldn't care at all

You asked about f-stop, but now I see you were thinking of exposure value. Quite a bit difference.

This depends on the unadultered noise, which depends on the ISO. It starts at about -8.8 EV with ISO 200; with ISO 800 it starts at about -7 EV.

I find it interesting that, according to DXOmark tests, the SNR and DR of the 5D MkII and 20D are approximately the same, at the pixel level

The "black noise" of the 20D (measured on the masked pixels) is almost twice as high than that of the 5D2 at ISO 100, and more than twice at ISO 1600. The effective noise of the 20D is correspondingly higher.

In other words: the DxO numbers are incorrect; there did occur some noticable development in the meantime.

[Ray]

The "black noise" of the 20D (measured on the masked pixels) is almost twice as high than that of the 5D2 at ISO 100, and more than twice at ISO 1600. The effective noise of the 20D is correspondingly higher.

In other words: the DxO numbers are incorrect; there did occur some noticable development in the meantime.

Well, that's interesting. Could this be the subject of another topic? Perhaps someone who owns both a 20D and 5D2 could post some sample comparisons of images with equal pixel count, employing the normal flawless technique of all good photographers.  

[aaykay]

I completely agree. The point is that Quentin didn't state he did any comparision camera to camera. He was just happy with the DR results of his A900 without comparing them to any other machine tested under the same scene. That's why I said he could be just enjoying an imaginary DR (I like this term Gabor introduced) which actually consisted in NR with detail being destroyed in the shadows.

Maybe Quentin had other dSLRs in the past, and in similar shooting scenes as the A900, never displayed the wide DR range that the A900 displays ?  Just a thought.

I personally am amazed at the level of detail the A900 retains, down into the deep darker regions of the image, while not blowing out the highlights.  Maybe the "Sony trick" of expanding the DR, is working, regardless of our "pixel-peeping" assumptions/findings ?  

[Panopeeper]

Maybe Quentin had other dSLRs in the past, and in similar shooting scenes as the A900, never displayed the wide DR range that the A900 displays ?

I envy those photogs who have such ability; they don't need any metering, neither auto nor external, for they simply know or see the required exposure.

I personally am amazed at the level of detail the A900 retains, down into the deep darker regions of the image, while not blowing out the highlights

I have no reason to shake your feeling or belief, but I do wonder how you want to know this, when

a. you don't (can't) know, how dark those regions are if the camera changes the intensities,

b. you don't know how much detail is really captured on sensor level, for you see only what the camera passed in the raw file.

See post #137.

Maybe the "Sony trick" of expanding the DR, is working, regardless of our "pixel-peeping" assumptions/findings ?

The Sony trick is not in expanding the DR but in creating the impression of an expanded DR. However, I do not think that this was intended; it is a side effect of the method.

As such, the unintended trick is a success, as your example proves it.

[Panopeeper]

Perhaps someone who owns both a 20D and 5D2 could post some sample comparisons of images with equal pixel count, employing the normal flawless technique of all good photographers

That's easy. Someone posts a shot of his/her cat, by a 5D2 and I post a shot of my dog made by the 20D. Then the normal flowless technique of all good photographers will immediately show, which sensor has higher noise on the pixel level.

[Quentin]

I completely agree. The point is that Quentin didn't state he did any comparision camera to camera. He was just happy with the DR results of his A900 without comparing them to any other machine tested under the same scene. That's why I said he could be just enjoying an imaginary DR (I like this term Gabor introduced) which actually consisted in NR with detail being destroyed in the shadows.

I've used quite a few different dslr's so I have my own personal baseline for comparison (is there any better?).

I honestly can't be bothered measuring and "proving" one way or another which camera has better dynamic range or lower noise.  You get a far better feel for these things though use.  The observations of others are of course useful and interesting, but ultimately they take a back seat to your own experience.

Thus, a camera I though clipped quite suddenly was the Olympus E3.  Cameras I found which had excellent dynamic range included the Kodak 14n, the DCS Pro 760C, the Nikon D700 and the Mamiya ZD.  And so on...

Tested against these and other cameras I have owned, used or tried, I remain of the view that the A900 is very good.  I can't compare with Canon as I have an irrational dislike of the brand  

YMMV

Quentin