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03-28-2011, 08:41 AM   #1
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Image size and sensor

So this question has been on my mind for a while and wonder if any of you know the answer. Suppose my camera is rated at 10 megapixels and I reduce the image size in the settings to 5 megapixels, now would the camera just crop the image on the sensor or will it use the entire sensor for the picture captured?

If it just crops the image on the sensor than it would be kind of pointless right? What about point and shoots? Do they work the same way?

Thanks

03-28-2011, 08:47 AM   #2
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They still use the whole sensor. The exception, I believe, is FF cameras that allow for the use of APS-C lenses. I think they only record only that part of the sensor that encompasses the APS-C dimensions, or at least that's all they output to jpeg.
03-28-2011, 09:00 AM   #3
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I would think that a small group of pixels would be collecting the same information on the same sensor. In the example you have, if you reduce from 10 to 5 megapixels, then every pair of pixels in the entire sensor would collect the same information. Just my guess....
03-28-2011, 09:41 AM   #4
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QuoteOriginally posted by Parallax Quote
They still use the whole sensor. The exception, I believe, is FF cameras that allow for the use of APS-C lenses. I think they only record only that part of the sensor that encompasses the APS-C dimensions, or at least that's all they output to jpeg.
Thanks. So the next obvious question is that since I hardly ever print my photos and don't really need that large mega pixel count, if I reduce the image size, would it mean I would get a better picture since same sensor size but less pixels or am I pushing it to far now? Lol

03-28-2011, 10:02 AM   #5
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QuoteOriginally posted by aamir515 Quote
Thanks. So the next obvious question is that since I hardly ever print my photos and don't really need that large mega pixel count, if I reduce the image size, would it mean I would get a better picture since same sensor size but less pixels or am I pushing it to far now? Lol
I assume you are shooting jpeg and not raw.
The picture quality would not be better, but if you are looking at the pictures at "fit to screen" resolution on your monitor, it shouldn't look any worse, either. The effect is the same as if you shot at 10, and then reduced it on your computer. The quality of the reprocessed image is going to be determined by the resample algorithm used to reduce its size, whether in-camera or in PP. The only thing you would be gaining is more images on a card due to the smaller file size. If that is of no consequence, then shoot at the best quality possible. You can always reduce the size later.
I never shoot jpeg at all. I shoot RAW because I prefer to have all of the information available when I do the PP instead of leaving what's important and what isn't up to whoever wrote the camera's firmware.
03-28-2011, 02:01 PM   #6
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QuoteOriginally posted by aamir515 Quote
Thanks. So the next obvious question is that since I hardly ever print my photos and don't really need that large mega pixel count, if I reduce the image size, would it mean I would get a better picture since same sensor size but less pixels or am I pushing it to far now? Lol
I rarely print my photos, but I do want them at higher than 1-2 MP resolution. If I didn't, I would go back and use my old pentax 2.1MP camera.

I shoot JPEGs but also crop down where full resolution still gives detail in the cropped image, and also sometimes print on really large paper 13 x 19 inch for example.

WHile I soot Jpeg, I use max resolution for the settings, and this allows for reasonable PP capabilities wothout needing the same space as RAW.

the fact is, while you never print, I'll bet you zoom in on your monitor, that is where you need resolution, My monitor is 22 inch, i.e. it almost perfectly replicates my 13 x 19 paper. BUT 1:1 pixel mapping means I need at least 8 monitors to view an entire K7 image for example
03-28-2011, 11:48 PM   #7
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QuoteOriginally posted by aamir515 Quote
So this question has been on my mind for a while and wonder if any of you know the answer. Suppose my camera is rated at 10 megapixels and I reduce the image size in the settings to 5 megapixels, now would the camera just crop the image on the sensor or will it use the entire sensor for the picture captured?

If it just crops the image on the sensor than it would be kind of pointless right? What about point and shoots? Do they work the same way?

Thanks
If the image was cropped from part of the sensor you would get different images (digital zoom effect) from different image sizes - you don't. It's averaged by the camera's processor from the whole sensor whatever size you have set the JPG to save at.
03-29-2011, 10:28 AM   #8
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QuoteOriginally posted by aamir515 Quote
If it just crops the image on the sensor than it would be kind of pointless right? What about point and shoots? Do they work the same way?

Thanks
point and shoots are made using sensors that are typically 8mm x 10mm. they have much smaller photo cites which is why they are pathetic (relitively) at high ISO, but the advantage of this is that a lens can be perhaps F3.2 at 20x or 500mm equivelent, which offsets somewhat the need for hither iso

03-29-2011, 07:39 PM   #9
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Thanks everyone for the explanations. Much appreciated.
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