Oly, perhaps a new player in this market segment

Started Aug 18, 2012 | Discussions thread
crames Regular Member • Posts: 192
Re: Oly, perhaps a new player in this market segment

bobn2 wrote:

crames wrote:

bobn2 wrote:

michaeljones wrote:

"If I crop in post and enlarge to the same size, then I get a noisier image than using the full frame. If I had set my shutter speed to the minimum that gave me an acceptably noisy photo, I will now find my output image is more noisy than acceptable, and will be wishing I had used a slower shutter speed or wider aperture when making the capture."

Bob, you wrote the above before.

Yes, I wrote that because it is correct, according to optical physics.

Bob, when I crop and enlarge, the image usually looks smoother, rather than noisier.

Really? Can you give us an example? If this was the case, surely we'd all be using crops rather than the full frame. And a P&S would be less noisy than a D800.

Wow! Is this really controversial? See below. Point being that the enlarged image has the same noise, as measured by its standard deviation. Obviously we don't all use crops because the signal is smoothed the same as the noise. And a P&S would be less noisy than a D800 only if it's pixels could capture more photons.

Where is the increased noise coming from when you enlarge? If not done badly, I would expect that enlarging/zooming/interpolating would neither increase nor decrease noise.

I explained in one of my replies to Michael. The noise is determined by the number of photons in the image. There are phewer photons in the crop, hence the crop is more noisy.

What matters in this case is the number of photons in the pixels, because that is what establishes the proportion of photon noise in each element of the image. The crop has the same proportion of photon noise, which doesn't change when enlarging .

What's confusing is that your example is not a demonstration of cropping and enlarging. It appears to be a down-sampling of the 36MP image to the size of the 15MP crop. Otherwise, how do you get from 10k to 24k photons? Of course the down-sampled image will have higher SNR (less noise) compared to the untouched 15MP crop, due to the combining of pixels.

Viewing two digital with different pixel counts the same size inevitably involves differently resampling. Resampling happens inevitably in your workflow

Right. But you have a choice of enlarging the smaller image, where the noise doen't change, vs. reducing the larger image, which decreases noise. Completely different results.

While down-sampling can reduce noise, it doesn't follow that up-sampling increases noise.

Upsampling is not a part of this scenario, simply that both images are sized to the same size, such that the camera pixellation is not visible in the viewed image (you wouldn't want it to be, anyway). Most every photo you view is resampled. Viewing at '100%' is a pure artificial test, so far as real photography is involved, and means comparing crops from different sized images.

Well, your scenario says "enlarge", so how does that happen without upsampling (Cameras don't "pixelate" - that is an artifact of the way one chooses to display an image.) Viewing at 100% has its uses, since it neither upsamples nor down-samples, leaving the pixels unmolested.

Can you present a scenario that illustrates how noise increases in an enlarged crop?

OK. Test for yourself. Fit a zoom lens. Set to double the minimum FL. Take a photo. Zoom to the minimum FL. Take a crop of the same framing as the original. Compare the the same size on any output medium there is. So long as the viewing conditions are sufficient to show noise, there will be more on the crop.

Depends on how you make them the same size . If you enlarge as you have originally proposed, the photon noise SNR doesn't change.

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