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Thread: Effect of image resolution

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    Effect of image resolution

    I have a compact camera (a Panasonic Lumix TZ1 and, as of today, a ZS7) and am trying to figure out the optimal settings w.r.t image quality.

    In particular, I want to understand how changing photo resolution affects noise. I have heard two theories:
    • reducing photo resolution also reduces noise, since more sensor elements now contribute to each pixel in the image
    • reducing photo resolution effectively INCREASES noise, since only a central portion of the CCD is used (PSNR per sensor element doesn't change, and each element now represents a larger percentage of the image)


    Anyone know which theory is correct? (Does it vary by brand, or compact Vs SLR?)
    Obviously, I'm rooting for the first theory

    Thanks!

    iestyn

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    JK6065's Avatar
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    Re: Effect of image resolution

    well I very interesting question you post here. I honestely don't know the answer but I'm quite curious.

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    Re: Effect of image resolution

    iestyn
    This sounds like a question for someone like Colin. Stick around for a couple of hours - New Zealanders should just be waking up about now!! Either that or he's already out on a dawn shoot.
    Last edited by Donald; 10th April 2010 at 06:54 PM.

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    Re: Effect of image resolution

    I'm waiting for Colin's answer too but I would think that as a general rule you would want your camera set to take pictures at maximum resolution. I don't think one would want to throw away pixels before seeing the image. If it turns out to be the shot of a lifetime and you threw away a good chunk of your pixels before you saw the image you will have to live with it. You can always throw away pixels after the fact.

    Chuck

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    Re: Effect of image resolution


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    Re: Effect of image resolution

    Quote Originally Posted by iestyn View Post
    I have a compact camera (a Panasonic Lumix TZ1 and, as of today, a ZS7) and am trying to figure out the optimal settings w.r.t image quality.

    In particular, I want to understand how changing photo resolution affects noise. I have heard two theories:
    • reducing photo resolution also reduces noise, since more sensor elements now contribute to each pixel in the image
    • reducing photo resolution effectively INCREASES noise, since only a central portion of the CCD is used (PSNR per sensor element doesn't change, and each element now represents a larger percentage of the image)


    Anyone know which theory is correct? (Does it vary by brand, or compact Vs SLR?)
    Obviously, I'm rooting for the first theory

    Thanks!

    iestyn
    Hi Iestyn,

    If all other factors are equal then the camera with the smaller number of pixels with have "bigger" pixels which will be more efficient at gathering light and will thus have less noise - but - if you're talking about "what setting to use" on your camera then be aware that this isn't changing the number of pixels on your sensor (which has a fixed number regardless) - it's only effectively changing the number that are used. So in that situation you'll capture less noise, but you'll also capture less information - so I suspect that the signal to noise ratio will probably remain the same (although I'm no expert in this area ... it's more one for Sean).

    On the other hand, if the camera does what's called "pixel binning" where the output from several pixels is effectively averaged then yes - you would see an advantage, but, you may just as well do that in post-processing afterwards.

    So my advice is to ALWAYS capture as much information as possible, and (to minimise noise in the first place), ALWAYS expose the shot correctly.

    We had a discussing here that you may also find interesting.

    Hope this helps

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    Re: Effect of image resolution

    Quote Originally Posted by Colin Southern View Post
    Hi Iestyn,

    if you're talking about "what setting to use" on your camera then be aware that this isn't changing the number of pixels on your sensor (which has a fixed number regardless) - it's only effectively changing the number that are used.
    Sorry I wasn't clearer... yes, that is exactly what I was wondering about - in my case, what the effect would be of choosing the "5MP" image setting on my 12MP camera.


    Quote Originally Posted by Colin Southern View Post
    On the other hand, if the camera does what's called "pixel binning" where the output from several pixels is effectively averaged then yes - you would see an advantage, but, you may just as well do that in post-processing afterwards.
    Okay, so that feature does exist then. I just don't know if it's ubiquitous or if it applies to my camera. Actually, on performing some tests this afternoon, it did unfortunately appear to be the case that the "5MP" mode simply used the central area of the CCD rather than doing any smart binning - this is backed up by the fact that the camera can obtain a higher optical zoom ratio (20x) in 5MP mode than it can (10x) in 12MP mode.


    Quote Originally Posted by Colin Southern View Post
    We had a discussing here that you may also find interesting.

    Hope this helps
    Hmm, it looks like several of the cameras under discussion there were doing the smart thing, where mine is not. Bummer! That seems like a really useful software feature to improve the generally abysmal low-light performance on compact CCDs (fewer, higher-quality pixels will definitely be an attractive trade in many situations).

    I had several reasons for wanting to use the 5MP mode myself - I wanted the extra zoom (which I now realise is incompatible with the 'binning' implementation you describe), I wanted to fit more photos on my memory card and I generally wanted to keep capturing, transferring and processing of images snappy (I take a lot of photos, so this is an issue for me!). I rarely crop or print my images, so they never really need to be more than monitor res; 3MP is usually plenty.

    Thanks for the responses, everyone! I guess I still need to keep waiting for a good 'small' SLR

    iestyn

  8. #8

    Re: Effect of image resolution

    "Sorry I wasn't clearer... yes, that is exactly what I was wondering about - in my case, what the effect would be of choosing the "5MP" image setting on my 12MP camera."
    Impossible to answer as there are too many factors to take into account. Amount of blurring in the low-pass filter (in front of the sensor to filter away IR and for protection purposes), level of noise reduction, resolution of lens etc (and more significantly, the aperature chosen) all contribute to the level of detail captured.

    I think these articles by luminious landscape is a good read to clarify your doubts.

    Understanding Digital Camera Resolution
    Counting Megapixels— All Megapixels Are Not Created Equal —
    How Big Can You Print?

    "5MP" mode simply used the central area of the CCD rather than doing any smart binning - this is backed up by the fact that the camera can obtain a higher optical zoom ratio (20x) in 5MP mode than it can (10x) in 12MP mode.
    Then that's simply cropping. Just to clarify some things... This process of "zooming" is called digital zoom. Varing the focal length is called optical zooming.

    fewer, higher-quality pixels will definitely be an attractive trade in many situations
    Slightly inaccurate, unfortunately!

    From this website's tutorial...

    No matter what the pixel size, larger sensors unavoidably have more light-gathering area. Theoretically, a larger sensor with smaller pixels will still have lower apparent noise (for a given print size) than a smaller sensor with larger pixels (and a resulting much lower total pixel count). This is because noise in the higher resolution camera gets enlarged less, even if it may look noisier at 100% on your computer screen. Alternatively, one could conceivably average adjacent pixels in the higher pixel count sensor (thereby reducing random noise) while still achieving the resolution of the lower pixel count sensor. This is why [COLOR=#afbddb]images downsized for the web and small prints[/COLOR] look so noise-free.
    If you were to downsize and apply noise reduction to a noisy, high mp image, you would get similar amount of noise and resolution from what you get with a less nosy, low mp image. Take for instance the Canon Mark 2 (24mp) vs Nikon D700 (12mp). The former has slighly higher noise when viewed at 100%, but if you were to downsize it to 12mp and apply noise reduction, the image looks similar, if not identical to the D700's. The mark 2, however, produces significantly higher resolution images at base ISO of 100.

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    Re: Effect of image resolution

    Quote Originally Posted by Colin Southern View Post

    So my advice is to ALWAYS capture as much information as possible, and (to minimise noise in the first place), ALWAYS expose the shot correctly.

    We had a discussing here that you may also find interesting.

    Hope this helps
    I think Colin made the correct remark. To reduce noise as much as possible correct exposure is very essential. Doing so you get the best out of your camera.

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