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

Started Jun 6, 2009 | Discussions thread
John Sheehy Forum Pro • Posts: 21,622
Re: 10mp vs 20mp

Steen Bay wrote:

Yes and no. I don't really buy the argument that the noise is already there in the lower resolution image, that we just can't see it!

We can see it. Just compensate the image size. Try this simulation; go into Photoshop and create a 400x400 square, and fill it with gray 128/128/128 (50%). Now, open the "Noise|Add noise" dialogue, in "preview" mode. Set the buttons to gaussian and chromatic (not monochrome), and play with the values until the square has noise just low enough that you don't see it (IOW, any higher would be visible).

Hit OK, and then hit CTRL ALT + or use the navigator to increase the zoom. The noise just seems to come out of nowhere, doesn't it?

Another simulation; take a noisy, but otherwise detailed image, and open the "Pixelate" dialogue in preview mode. Try different tile sizes, from 2 to 24. Do any really look better than the original? This is roughly analogous to maintaining the same sensor size but varying the pixel density.

It's a bit like saying that above the clouds the sun is always shining. It doesn't really help much. Higher resolution is a nice thing, but it comes at the cost of more noise. It's a trade, no reason to hide that.

It's not a matter of hiding it; it is a matter of it not being true most of the time. The G10 does not have more image noise than early G cameras. The G11 has less image noise because the technology has been substantially improved, and/or the readout has been slowed down.

And won't a 20mp G11 have one stop less DR that can't be recovered with downsampling?

In order to have 1 stop less DR by the engineer's definition, read noise at the pixel level relative to saturation would have to increase to 282% of the 10MP; in "electrons" that would require an increase to 141%.

Based on Canon's history, they will probably not increase the density in the series until it can be done without substantially increasing the image-level read noise.

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John

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