One of the criteria that every camera review site uses in evaluating the quality of a new camera is image noise. As ISO increases noise normally increases as the sensor capture capabilities (or lack thereof) and boost processing electronics take their toll on the quality of the captured image.

There are many things that affect that noise, not the least of which is the size of the light-gathering pixels that capture the image. As discussed in detail in The Digital Sensor and The Digital Sensor Part 2, the size of the photosite is the reason the tiny sensors used in pocket point and shoot cameras are so limited in capabilities compared to the Digital SLR, which is where the major growth in the photographic market is now occurring.


The impact of photosite size is ably demonstrated in one of today's hottest DSLR cameras - the Nikon D3. This $5000 camera is a 12.2MP full-frame camera. Since it can also handle Nikon DX crop lenses and create a 5MP image at the common APS-C size seen in most of today's DSLR cameras, it is easy to understand that this 12MP full-frame has the same photosite size as a 5MP crop-sensor DSLR.

As discussed in detail in the Digital Sensor articles, the sensor is an analog light-gathering device. It is not a simple digital on-or-off digital device where size really matters very little. In a camera sensor the light gathering is analog and the larger the light gathering area, all else being equal, the better the light gathering ability.

Compared to today's 10 to 14.6MP sensors in top DSLR cameras with a 14x24 sensor, the Nikon D3 has huge photosites in its 24x36mm 12MP sensor. Combined with CMOS technology and evolved electronics the Nikon D3 has a normal ISO range to ISO 6400. As a comparison, the Canon XSI top sensitivity is 1600 and most prosumer models extend to ISO 3200.


As you can see in this dramatic ISO 6400 hockey shot produced by Dave Black for Nikon, D3 images at ISO 6400 are extremely low noise. Even more impressive is the ability to still capture usable images at ISO 12800 and all the way to ISO 25600 with much increased noise in a pinch.

Clearly noise is related to the size of pixels in analog sensors, but that is only part of the story. Often the manufacturer of the camera has made decisions, either informed or due to lack of expertise, to not process for noise at high ISO. Cameras that appear to exhibit much increased noise at high ISOs are sometimes capable of much lower noise. The poor noise performance is sometimes the result of decisions by the camera maker in how files will be converted to RAW or JPEG files in camera or in post-processing software.

The Sigma SD14 Wakeup Call
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  • n4bby - Monday, July 28, 2008 - link

    agreed. i criticized some earlier reviews, but was holding out for the quality of writing and analysis to improve. that is clearly not happening. even the article synopsis in my anandtech RSS feed was completely wrong:

    "Not all JPEG processing is created equal, but Noiseware can often fix what camera JPEG processing leaves undone...."

    i was truly puzzled by this. noise reduction has NOTHING to do with JPEG compression - that's like saying, "not all gasoline is created equal... let's see how this motor oil performs."

    but i guess if it brings in the ad dollars, it's mission accomplished for the site... even though ultimately it's doing the readers a disservice.
    Reply
  • Wesley Fink - Tuesday, July 29, 2008 - link

    You are technically correct, but it appears you are straining to make your point. Certainly you, and everyone else, understands that noise reduction is one of the processes that usually happens during in-camera "JPEG" processing or during software conversion from RAW to a finished image format which is normally JPEG, but could be TIFF or even another format.

    In the interest of being more precise in the description I have changed it to:

    "Not all image processing is created equal, but Noiseware can often reduce noise that in-camera or software processing leaves behind."
    Reply
  • n4bby - Tuesday, July 29, 2008 - link

    thank you for fixing that.

    "Not all image processing is created equal, but Noiseware can often reduce noise that in-camera or software processing leaves behind."

    so does gaussian blur! ;)
    Reply
  • soydios - Monday, July 28, 2008 - link

    Eh, I'd say that your quoted caption is an accurate description of the article. There's on-chip noise reduction that is performed before the RAW file is created, then there's software noise reduction that is performed as part of the image processing engine in-camera. The output of that image processing engine is usually JPEG or TIFF, and the RAW preview image.

    So, if a camera's processing engine isn't running noise reduction before writing to JPEG, then this software would finish the noise reduction stage of post-processing.

    As for the software itself, I don't know about the images at full magnification, but the small previews shown indicate fairly heavy smearing. Lightroom does less smearing, and seems to be extremely capable in my experience at chroma noise reduction, and good enough at luminance.

    As for writing quality, I can't do better, so I won't criticize.
    Reply
  • n4bby - Monday, July 28, 2008 - link

    it is NOT an accurate description. image processing has NOTHING to do with the final output format of the file. you said it yourself - the output could be TIFF, so what does it have to do with "JPEG processing"? call it a nit if you will, but anandtech is a technical publication, so such fundamental inaccuracies should be considered anathema.

    and saying you can't criticize because you can't do any better yourself seems symptomatic of the sort of mediocrity malaise that results in sub-standard institutions like the US Postal Service. ;) if we expected everything in the world to be no better than what we ourselves can accomplish, the world would be a very sad place...
    Reply
  • guitargeek27 - Monday, July 28, 2008 - link

    It's kinda unfair to compare the noise of a Nikon D3 to a Canon XSI, as the Canon has a smaller sensor (as well as a few thousand dollars less)

    If you wanted to be fair, how about comparing the D3 to a Canon 5D (full frame and less expensive than the d3) or the EOS 1D Mark II or III?
    Reply
  • Spoelie - Monday, July 28, 2008 - link

    Personally I think there's too much smearing going on, to the point that I like the original picture better. The first picture for example has quite a loss of detail on the windows of the buildings and on the slope of the mountain. In the second picture all the ripples are gone and the boat seems to float above instead of in the water. All non-macro low-iso shots show an incredible amount of smearing (stones on the stairway, vegetation on every background mountain, ripples in water). I don't know how anyone would consider those filtered low-ISO shots an improvement. Reply
  • cparka23 - Monday, July 28, 2008 - link

    I've long been impressed w/ Canon's low noise compared to other makes. Up 'til now, I've always heard/assumed that it was the sensor. So is it possible to determine to what exactly the noise reduction is attributable in many cameras? Is it due to an algorithm or is it really the sensor? I guess we'll never know, since the images are already 'processed' in RAW, will we? Reply
  • cparka23 - Monday, July 28, 2008 - link

    hmm.. after rereading, that first question didn't come across as I had entirely hoped. regardless, the article helped me understand this a bit.

    Thanks, Wes.
    Reply
  • strikeback03 - Monday, July 28, 2008 - link

    Canon states that the only noise reduction done to their RAW images is dark noise subtraction. They have plenty of whitepapers on their technology floating around. Reply

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