Pixel density - can the playing field be leveled???

Started Jun 6, 2009 | Discussions thread
Graystar Veteran Member • Posts: 8,373
Re: The answer of your question is right here

Jay Turberville wrote:

I’ll believe when I see it. And so far, I haven't seen it.

I just showed you an example of it, but have now included another

I’m having trouble following all this in relation to the OP’s opening question. The OP asked...

briander wrote:

If two camera's
have the same size sensor, and one is a 10 MP, and the other is a 15
MP, and I lower the resolution on the 15 MP to 10, can I expect the
same picture quality for a noise perspective? Of course, this is
putting all of the other camera functions (noise reduction, etc)
aside.

So there are two parts to this question. The first is what happens when you lower the resolution of the image from 15MP to 10MP. The second question is, essentially, what happens when you compare sensors of similar size but different densities.

On resizing...

I said that resizing an image doesn’t change the noise level. It simply makes the noise smaller, as with everything else in the image. When said image is printed at the same size as the original, it will have the same noise.

You’re saying that’s not the case. You’re saying that a “proper” downsampling process starts with a low-pass filter, and you provide images to that effect.

The problem I have with this is that a low-pass filter is a noise reduction process that has nothing to do with resolution reduction. I consider the application of the low-pass filter prior to image reduction to be unjustified when the intent is to perform a qualitative comparison to the original image. I could just as easily apply the low-pass filter to the original image and have matching noise levels but more detail than the reduced image. What is the justification to not do so? There is none. There’s no reason to say, “Applying a low pass filter to the original is unfair to the upcoming comparison.”

The only thing you can say about your processing is that the end result may have less noise (at the expense of detail) than an untouched original. But it’s not going to be better than the original with matching noise reduction applied. At best the noise levels will be the same, which is what I’m saying.

So here’s a challenge. Take a noisy image...
Apply a low pass filter and print at 8x10...
“Properly” resize image to reduce noise and print at 8x10...

Present images of the prints for comparison. If the images show that the resized print has less noise with equal detail, then I’ll reconsider my position.

Here’s an image...
http://home.roadrunner.com/~graystar/yo800.jpg
Here’s the control...
http://home.roadrunner.com/~graystar/yo80.jpg

On the equal sized sensor comparison...

The sensor comparison will simply follow the results above. If, somehow, the downsampling of a high-res image can actually produce a better print (at the same size) as a processed lower-res image, then there’s no question that we would want higher pixel densities on our sensors. So we have to first get clear resolution on the resizing question, which (at least to me) your analysis doesn’t provide because you didn’t compare the resized image to the original size, low pass filtered image.

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cpw
cpw
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