Reasons for wanting higher mega pixel count

Started 3 months ago | Discussions thread
JimKasson
JimKasson Forum Pro • Posts: 26,239
Re: Reasons for wanting higher mega pixel count
1

Scottelly wrote:

JimKasson wrote:

canonpfs wrote:

Much is said about the Sony A7R IV's "too high" mega pixel count. It seems the only reason that people can think of for needing a high mega pixel count is cropping. Besides cropping, here are two additional reasons for wanting more mega pixels:

1. Sharper images. Have you ever looked at an image on your rear LCD and thought that they were sharp only to find them blurry on your home monitor? Yes, I know we should look at our images on the LCD at higher magnifications but please bear with me for a moment. The reason why the blurry images looked sharp on the LCD is because a large image is displayed very small. So you shoot in low light and there is a breeze. You are already at a high ISO to get a higher shutter speed but the flowers in the foreground are still slightly out of focus. With lots of mega pixels available this image can be down sampled. At a smaller size the flowers are now sharp. Taking an image from 61MP down to say 18MP sharpens slightly out of focus areas.

That is true, but it's a second order effect if the CoC of the blurry flowers is much bigger than the pixel pitch. It occurs because the sharpening algorithms work better with more samples. By the time the CoC gets to 4 or 5 pixel pitches, the improvement is virtually gone.

2. Lower noise. Provided the 61MP sensor provides the same high ISO performance as the 42MP sensor the larger sensor will result in lower noise when down sampled. Noise just seems to magically disappear with down sampling. So if you have noise in the 61MP image just down sample it and the perceptible noise will be less.

This is true if you use nonlinear noise reduction. If you use linear noise reduction, it's pretty close to a wash, since the full well capacity for a given sensor technology is mainly proportional to the area of the pixel.

This is something I've been reading for years and years, yet the new 61 MP Sony sensor offers more dynamic range than a similar sized (full-frame) 42 MP Sony sensor. Since the technology is mature, and since both are back-lit sensors that have basically maxed out their possible fill-factor, shouldn't the 42 MP sensor offer more dynamic range, rather than less, if what you're saying is really true?

You are ignoring the words "for a given sensor technology" in the above. That is meant only to apply within a sensor generation, not across generations.

This concept of photo-sites with larger area being better for dynamic range bothered me when the Nikon D7100 came out, offering more dynamic range than any previous full-frame camera from Nikon or Canon, despite the photo-sites having a much smaller surface area. Nobody was ever able to explain to me why the little, APS-C sensor could capture so much more dynamic range than the older full-frame sensors. Sure, they said there was newer technology in the Nikon D7100 sensor, but that only goes so far, when people continue to make claims like this one you've just made. Given the fact that technology continues to improve, I don't see how what you're saying can be applicable, yet people keep saying stuff like, "They can't get much more out of a sensor, because the limits of the laws of physics have nearly been reached."

Have you ever seen me make that claim, except in the case of QE?

I've read comments like that for more than ten years, yet camera/sensor companies keep on making sensors that have smaller photo-sites, yet can somehow capture more dynamic range.

What are your thoughts on this Jim?

It's unclear to me at this point how much Claff PDR improvement the a7RIV offers over the a7RIII. It is true that full well capacities (FWCs) per square um tend to (fractionally) increase with each generation, and that read noise (RN) tends to decrease, so I would expect some PDR improvement. I would expect EDR -- unnormalized EDR, which is the only form I think makes sense -- to get somewhat better because of RN decreases, but again, at this point the is unknown, as Sony has not provided the protocol for their EDR claims.

Over time, as the pitches become finer, Claff PDR becomes more a measure of RN and less one of FWC, but we are a long way from the RN being the only important component, so, within a generation of sensor technology, I'd expect PDR to be about the same regardless of pitch.

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