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11-04-2010, 08:08 PM   #1
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Image Size

When I change the image size in my K-x from 12 megapixels to 10, to 6, etc., what is the camera actually doing? Does it record fewer pixels from the sensor? If so, which pixels does it use? Does the different pixel pattern affect the image (aside from the obvious loss of resolution) Or, is the change in image size basically a software function where the camera takes several pixels and processes them as one?
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11-04-2010, 08:17 PM   #2
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I don't know.

But If I had to guess, I would not say it's happening at sensor.

I would guess that the picture is taken, then software resizes the photo, as you would in photoshop or aperture or gimp.
11-04-2010, 10:52 PM   #3
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My understanding is that the camera record at full resolution (eg 12 Mp) and then process/convert the RAW data into JPEG. I do not know the algorithms, but there must be some computations involved from 12 Mp to 10 Mp.

This is why the K-5 has a function to convert a JPEG into RAW as long as the original data are in the camera buffer.

I cannot guarantee that I am right however for K-x and K-7, but I am probably not far.
11-05-2010, 05:53 PM   #4
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Thanks for the information. If the camera really combines pixels via software to get the resized image that raises an interesting question about noise, since the pixels are analog sensors.
I know an electrical engineer could straighten me out on this, but here's my theory. For the sake of example, we set the camera to produce a 6 mp image instead of 12mp By combining two real pixels into the new single "virtual" pixel" you would double both the signal and the noise. So the S/N ratio would remain the same. But since you have now doubled the total signal, you can attenuate it lower, also lowering the noise below the threshold of detection.
Now in experimenting with the different settings, this clearly isn't the case. But if engineers could figure it out, it would be neat trick. Just imagine the low light response you'd have at a 2mp setting.

11-09-2010, 10:20 AM   #5
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QuoteOriginally posted by tcwilson Quote
Thanks for the information. If the camera really combines pixels via software to get the resized image that raises an interesting question about noise, since the pixels are analog sensors.
I know an electrical engineer could straighten me out on this, but here's my theory. For the sake of example, we set the camera to produce a 6 mp image instead of 12mp By combining two real pixels into the new single "virtual" pixel" you would double both the signal and the noise. So the S/N ratio would remain the same. But since you have now doubled the total signal, you can attenuate it lower, also lowering the noise below the threshold of detection.
Now in experimenting with the different settings, this clearly isn't the case. But if engineers could figure it out, it would be neat trick. Just imagine the low light response you'd have at a 2mp setting.
And that's pretty much what you get when you downsize your image (in Photoshop or whatever) to 1000-pixels wide, the noise doesn't appear to be "as noisy"

The camera most certainly uses a similar process (software algorithm) to downsize the image prior to saving it on the card.
11-09-2010, 06:26 PM   #6
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QuoteOriginally posted by tcwilson Quote
Thanks for the information. If the camera really combines pixels via software to get the resized image that raises an interesting question about noise, since the pixels are analog sensors.
I know an electrical engineer could straighten me out on this, but here's my theory. For the sake of example, we set the camera to produce a 6 mp image instead of 12mp By combining two real pixels into the new single "virtual" pixel" you would double both the signal and the noise. So the S/N ratio would remain the same. But since you have now doubled the total signal, you can attenuate it lower, also lowering the noise below the threshold of detection.
Now in experimenting with the different settings, this clearly isn't the case. But if engineers could figure it out, it would be neat trick. Just imagine the low light response you'd have at a 2mp setting.
Fujifilm did something along those lines in a few of their P&S cameras, called EXR. dpreview talk a bit about how it works in this review: Fujifilm FinePix F200EXR Review: 2. EXR technology: Digital Photography Review

I owned the F200 for a while and I can confirm that the system does work well, although I found it more useful for giving me extra dynamic range than reducing noise.
11-10-2010, 07:29 PM   #7
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Thank you for the information. I appreciate your taking the time to reply.
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