Gear Talk > EOS Bodies - For Stills

24 cameras now pushed and compared for noise on the dark end at all ISOs

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Aglet:

--- Quote from: Mt Spokane Photography on April 15, 2012, 01:39:45 PM ---Its pretty apparent from the comments that intrepreting what you are showing is not being understood the same way by users.  Thats why signal to noise ratios are a good way to help people understand.

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Its the brightness or luminance of the noise with respect to the image signal (S/N ratio) that determines how much noise shows in your image.
 
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--- End quote ---


Nicely and succinctly re-stated, thank you.
This is what I'll be trying to convey to a wider audience on my (as yet incomplete) techblog on this topic by showing some real-world samples.
http://a2bart.com/tech/darknoise.htm

however, SNR can be looked at in imaging in a couple different ways and that's also important:

1. average signal to average noise ratio - not good as it obscures the impact large value (bright) noise can have
This seems to be a method a many review sites use (e.g. DxOmark print measurement) and that can lead to some skewed results and unhappy buyers of noisy cameras but this is also an effect of scaling images (downwards) for printing so it's not without some merit, especially when camera resolution is quite high compared to the final print size. I.E. 20MP image file printed to a 7 or 8MP print file.

2. signal to peak noise ratio - much better representation as small bright noise is more accurately weighted against the (image) signal level and it's something we perceive very readily as our eyes are contrast detection devices.  This is even more obvious to us if there is a pattern to it, even just a simple line will become quite obvious.  This is most apparent when "pixel-peeping" at full size on screen but can also be a factor when printing very large prints where individual pixel level noise can be seen on the print at close distances.  or when using noisy lower resolution image files to make moderate size prints.


I've actually got some really good examples of this from real world shots to show, just no time to prep them yet.

zwoop:
Did you account for ISO differences between cameras?

For example, ISO 200 on the 5D2 is about ISO 143. The 50D's ISO 100 is about ISO 157. DxoMark has all the numbers.

http://www.adorama.com/alc/article/11227

marekjoz:
Aglet -thanks for this wonderful job.
I'm a bit surprised somewhere there:
1. 7d looks better than 5d2, what is difficult to be confirmed by me as I use both.
2. I'm surprised with g1x which looks awfull in comparison to g12.

Because of question No 1: have you assured the same conditions during tests? As conditions for Darks I can't imagine anything else as same temperature (also not so, that camera has shot before 100 photos and after that you took a sample dark frame). Were the baterries fully charged? Noise reduction of course Off?
What was the exposure time? Have you tried different exposure times and compare it also in this dimension?

I'm asking just because of observation No 1 - If my experiences from using both show something different,  then how can I trust and interprete the rest?

TrumpetPower!:
First, pushing shadows by four stops is about as meaningless as it gets. If you were to pull the highlights by an equivalent amount, you'd be attempting to add eight stops of dynamic range to the camera, basically doubling your DR. If you're trying to do that in the real world, either you know full well that the results are going to be crap or you're merging multiple exposures with HDR.

But even if you're only doing this to make the quality of the noise more visible, it's still a meaningless test because you're comparing 100% crops. A 100% crop of a 50 megapickle image can look much, much worse than a 100% crop of a 10 megapickle image and yet the 50 megapickle image might make a print that blows away the 10 megapickle one.

If you're serious about this, what you want is to pick a representative final print size -- 13" x 19" would be typical of the largest likely print size owners of those cameras might have in common -- and then scale, up or down as needs be, all the images to 100 ppi at that size. For this example, that would be 1300 x 1950 (to preserve the aspect ratio). You can then take a 100% crop of the 1300 x 1950 resized image for your comparison.

Why only 100 ppi instead of the 300 ppi you'd be printing at? Well, 300 ppi would make sense if you were going to print these, but you and everybody else will be making the comparisons on screen and not on paper.

Of course, the real way to do this kind of comparison would be with real-world images that get put through the full post-production workflow all the way to final prints, and then compare those prints...but nobody seems to do that sort of thing. I'm guessing it's because those who make prints don't waste their time with these sorts of tests, and those who waste their time with these sorts of tests don't make prints.

Cheers,

b&

Marsu42:

--- Quote from: marekjoz on April 15, 2012, 02:16:36 PM ---Aglet -thanks for this wonderful job.  I'm a bit surprised somewhere there: 7d looks better than 5d2, what is difficult to be confirmed by me as I use both.

--- End quote ---

First, thanks for the effort to Aglet! My 2 cents critique:

* Comparing Canon to Sony's sensors (Nikon, Pentax): It is indeed the question how valid such an extreme underexposure and successive +ev correction is, or Canon would be broke by tomorrow. My idea: maybe another test with a dark grey background and moderate underexposure and post-processing +ev correction would put this into perspective? This is because that somewhat clever post-processing (software) will never try to raise black parts as far as you did.

* To me, the thing that kills my shots is banding. I guess there is no scientific number to measure this? If not, downsized shots would indeed offer a better basis for comparison since they'd show how much noise *pattern* is left.

* But most of all, I am stunned how much worse the 7d looks in this artificial test in comparison to the 60d. I have heard that the 7d is more prone to banding, but I'd never dared to mention it here because I'd get stomped. But looking at your 7d/60d pictures... am I missing something? They do use the same sensor, don't they? Is this banding due to some other processing in the 7d's dual digic cpus?

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