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:

All well and good, but that wasn't the OP's question.

OP’s question was, ultimately, about image quality...

“...can I expect the same picture quality for a noise perspective?”

And image quality can only be fairly evaluated when the images are the same physical size. That’s why prints are important.

2) The printing process and scale may preserve all of the image
detail and noise of both comparison images,

That’s exactly what happens with all current inkjet printers, except for the really small print sizes.

If we imagine a crop of our two images from two different density
sensors on two display devices that show the images at 100% pixels,
and then move the higher resolution image further away until it has
the same apparent image detail size as the lower resolution image
(same viewing scale), we will observe that the size of the noise in
the higher resolution image gets smaller and becomes less obtrusive.
But, of course we know that the noise did not actually go away or
change in any way.

Yes, I’ve described this same scenario in several posts to help people understand why resizing images doesn’t reduce noise.

But if we view the images such that the lower resolution image is
being viewed where its finest detail is right at the limit of visual
acuity, we can be assured that in the viewer's eye that some noise
and some image detail in the higher resolution image hasn't simply
become smaller and less obtrusive. It is actually no longer visible.
The viewer's eye (lens and/or retina) is acting like a low pass
filter. The eye limits the resolution. The image the brain sees is
a version with less resolution. This is more akin to what I've been
describing. When real resolution is reduced, some real noise is also
reduced. This is the answer to the question that the OP posed.

But you’re forgetting the scenario you just described. When the full-res image, with all its information available, is viewed at the same apparent size as your resized example, a similar effect will occur...the image will appear to have less noise. What both images really have is simply less discernable detail...one because the detail isn’t there, and the other because the detail is too small to see. The visual results are exactly the same.

Only a printer has the resolution to create detail smaller than we can discern. That’s why I say that to prove that your 15 MP image actually has less noise when resized to 10 MP, you have to print every pixel of the original 15MP image at 600DPI and then print the 10MP image at the same size. If you’re right then the two images should have the same discernable detail, while the 10 MP image has less apparent noise.

But I can already tell you...that’s not going to happen. The images will look the same, and will match a 10 MP print from a 10 MP sensor.

There’s no side-by-side comparison you can display on a computer screen that will demonstrate this. You need to produce images at the same physical size with different resolutions.

I have two 21” CRTs side by side and I’ve tried viewing a 1600x1200 image and the same image resized to 800x600 after having a 1-pixel Gaussian blur applied. I step back about 8 ft to ensure that previously seen minute detail in the 1600x1200 image is no longer discernable, and the images look identical.

But maybe I did something wrong in the resizing. If you take the image I posted earlier, cut a 1600x1200 crop from it, resized it to 800x600 and post it then I can look again to see if I notice less noise on the resized image. Otherwise, only a printer will have the resolution range to demonstrate your senario.

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