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01-26-2020, 06:38 AM   #1
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High pixel density and image softness?

It's counter-intuitive - I had the idea that the greater the pixel density (i.e., very small pixel pitch), that you'd get sharper images. This guy, in his discussion of diffraction and how the aperture affects image softening, shows why one has to be more careful about such settings with a higher-density sensor. (With the implication that my KP isn't just a K-1 in a smaller package.)



01-26-2020, 07:34 AM - 1 Like   #2
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Sort of true... sort of not....

Yes, both diffraction and the limitations of optical design and manufacturing can create limits on the sharpness of the RAW image.

Worse, small pixels also impose a limit on how much sharpening can be done in post without creating a ton of noise in the final image.

That said, with a given lens and a given scene, a 24 MPix APS-C image from the KP will out-resolve a 15 MPix cropped image from the K-1. (But assuming decent "equivalent" lenses, a 24 MPix FF image will out-resolve a 24 MPix APS-C image.)

The result: greater pixel density always provides more information about the scene than does lower pixel density but the improvement is never as great as one might hope because these other optical and noise limitations attenuate the improvement in sharpness.
01-26-2020, 07:41 AM - 1 Like   #3
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IDK. The Equivalence of Pixel Pitch ? My opinion is that he's getting carried away with theory which probably can't be seen in real world. I would think that with higher density sensors shutter slap, mirror slap, and bad technique would show up before any pixel pitch diffraction could even be detected. My 2 cents
01-26-2020, 11:23 AM - 1 Like   #4
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QuoteOriginally posted by thazooo Quote
IDK. The Equivalence of Pixel Pitch ?
It just goes to show that just about anything can be addressed by overthinking.


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01-26-2020, 11:43 AM   #5
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QuoteOriginally posted by thazooo Quote
IDK. The Equivalence of Pixel Pitch ? My opinion is that he's getting carried away with theory which probably can't be seen in real world. I would think that with higher density sensors shutter slap, mirror slap, and bad technique would show up before any pixel pitch diffraction could even be detected. My 2 cents
I cannot agree on that one. It is neither very theoretical nor a non issue.
However, by using good algorithms you can make a interpolation similar to the results of a lower resolution sensor and than sharp it using information available from before interpolation (searching for over multiple pxl existing contrasts that got removed ot washed out during interpolation resulting in a photograph containing more information than with a lower resolution camera.
The truth however is, we do not do this on our picture thous his claims stay true.
01-26-2020, 02:34 PM - 3 Likes   #6
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If you have a 50 megapixel full frame sensor and a 24 megapixel sensor and you stop them both down to f16, you probably won't see much more resolution with the 50 megapixel sensor than with the 24 megapixel sensor, but you certainly won't see less. To me, this just means that with high megapixel sensors you have to use wider apertures and maybe do some focus stacking to get optimal results. Or just stop down and don't worry about it.
01-26-2020, 06:29 PM   #7
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QuoteOriginally posted by Rondec Quote
If you have a 50 megapixel full frame sensor and a 24 megapixel sensor and you stop them both down to f16, you probably won't see much more resolution with the 50 megapixel sensor than with the 24 megapixel sensor, but you certainly won't see less. To me, this just means that with high megapixel sensors you have to use wider apertures and maybe do some focus stacking to get optimal results. Or just stop down and don't worry about it.
Yup, best advice is to not worry about it. Diffraction is never an absolute limit to attaining detail, it just causes diminishing returns. If shooting at f/22 on 35mm film back in the day could produce usable results, then the same aperture on a 50mp FF sensor should produce results at the very least just as usable. The race between increasing megapixel counts and bar-raisng MTF scores means that people too often focus on pixelpeeping at or above 100% magnification, rather than the actual appearance of the full composition at a practical display size. As for cropping, if someone ever needed to crop so much that either diffraction or digital upscaling was noticeably ruining image quality, then that's really just tough luck because clearly the shot was made at the wrong focal length.

Optimal sharpness is another matter, and if someone really cares for it that much then they shouldn't mind shooting every photo on a tripod with pixel shift and focus stacking and the most expensive lenses money can buy, because no matter how many megapixels you have, optimal IQ is always hard-limited by technique and circumstance.
01-27-2020, 12:45 AM   #8
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Another Tuber with a channel to fill? Can you see a new camera being advertised as “so high a resolution you can’t tell the difference from our last model!!” ? Go out and take photographs instead, why don’t you.

01-27-2020, 01:37 AM   #9
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If it bothers you do the very same and stop reading technical posts.
01-27-2020, 02:02 AM   #10
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QuoteOriginally posted by StiffLegged Quote
Another Tuber with a channel to fill? Can you see a new camera being advertised as ďso high a resolution you canít tell the difference from our last model!!Ē ? Go out and take photographs instead, why donít you.
+1
Itís gonna take all the fun and magic out of photography if we keep focusing on technical specs than the actual process.
01-27-2020, 03:40 AM - 1 Like   #11
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QuoteOriginally posted by WorksAsIntended Quote
If it bothers you do the very same and stop reading technical posts.
It doesnít, I do, Iíll read what I like. The OP invites comments by posting, my thoughts on the subject are as posted. Have a bacon sandwich, theyíre delicious. 😋
01-27-2020, 06:05 AM   #12
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QuoteOriginally posted by StiffLegged Quote
Another Tuber with a channel to fill? Can you see a new camera being advertised as ďso high a resolution you canít tell the difference from our last model!!Ē ? Go out and take photographs instead, why donít you.
LOL......Olympus EPL series ?.....LOL, great.
01-27-2020, 12:18 PM   #13
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QuoteOriginally posted by Rondec Quote
Or just stop down and don't worry about it.
It is amazing how well this approach has worked over the years for large format film photography. Yes, that sounds glib since there are no pixels. OTOH, these questions regarding diffraction limits are limited in application to testing labs and actual prints. If the results pass muster at the desired print size and reasonable viewing distance, than all is good. To be honest, I doubt if most of us have sharp enough lenses to justify worry about pixel density.


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01-27-2020, 12:36 PM - 2 Likes   #14
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In the interest of staying true to the "tech" element of this thread, the Wikipedia can be very helpful at times and interestingly enough, there is a paragraph in the article on Diffraction-limited System that summarizes the concerns for digital photography as copied below. Of particular interest are the three operating regimes...

QuoteQuote:
In a digital camera, diffraction effects interact with the effects of the regular pixel grid. The combined effect of the different parts of an optical system is determined by the convolution of the point spread functions (PSF). The point spread function of a diffraction limited lens is simply the Airy disk. The point spread function of the camera, otherwise called the instrument response function (IRF) can be approximated by a rectangle function, with a width equivalent to the pixel pitch. A more complete derivation of the modulation transfer function (derived from the PSF) of image sensors is given by Fliegel.[3] Whatever the exact instrument response function, it is largely independent of the f-number of the lens. Thus at different f-numbers a camera may operate in three different regimes, as follows:
  1. In the case where the spread of the IRF is small with respect to the spread of the diffraction PSF, in which case the system may be said to be essentially diffraction limited (so long as the lens itself is diffraction limited).
  2. In the case where the spread of the diffraction PSF is small with respect to the IRF, in which case the system is instrument limited.
  3. In the case where the spread of the PSF and IRF are of the same order of magnitude, in which case both impact the available resolution of the system.

The spread of the diffraction-limited PSF is approximated by the diameter of the first null of the Airy disk,

d / 2 = 1.22 λ N

where λ is the wavelength of the light and N is the f-number of the imaging optics. For f/8 and green (0.5 μm wavelength) light, d = 9.76 μm. This is of the same order of magnitude as the pixel size for the majority of commercially available 'full frame' (43mm sensor diagonal) cameras and so these will operate in regime 3 for f-numbers around 8 (few lenses are close to diffraction limited at f-numbers smaller than 8). Cameras with smaller sensors will tend to have smaller pixels, but their lenses will be designed for use at smaller f-numbers and it is likely that they will also operate in regime 3 for those f-numbers for which their lenses are diffraction limited.
Diffraction-limited system - Wikipedia

For those interested in reading the Fliegel reference, the pdf is linked below...

Fliegel, Karel (December 2004). "Modeling and Measurement of Image Sensor Characteristics" (PDF). Radioengineering. 13 (4)


Steve

Last edited by stevebrot; 01-27-2020 at 12:43 PM.
01-28-2020, 04:48 AM - 1 Like   #15
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Thanks for all the clarification, y'all. The guy in the vid did say he was oversimplifying for the sake of communication; but his conclusion as I understood it, was that the "folk wisdom" assumption that you will get an increasingly sharper image as the iris contracts is false, because at some point, given a combination of lens and sensor, fuzziness will begin to increase, resulting in a softer overall image. @Stevebrot's Wikipedia quote seems to suggest that's not true, either.

I, myself, am seriously math-challenged and color-blind (or alternatively, resolution-enhanced). I don't see colors as well as other people in the red-to-green realm, but the lack of huge color photoreceptors in the retina is made up by zillions more luminosity photoreceptors - more pixels per unit of surface area in the retina (wolf-vision - I can see clearly when people with normal color-vision think it's pitch dark). So image quality is a high priority for me, hence my "technical" interest. So, @StiffLegged, I can see a difference, or at least am more likely to be able to than most photographers.

There are so many parameters of image quality, that isolating the effects of one by looking at pictures is impossible. But I figure that if I can adjust how I take pictures to optimize as many as I can, I'll be able to improve my results. And I've been hearing people complain about diffraction, all the official lens reviews try to evaluate it, and I can't say that I've ever understood what all the fuss was about. But since there is a fuss, and I'm trying to get better, telling me, "there, there, poor baby, just go and take pictures and don't worry your li'l pea-brain about it" isn't really very helpful.

And, tangentially, as to @mixalis_kalymnos1611's observation that, "It’s gonna take all the fun and magic out of photography if we keep focusing on technical specs than the actual process." I'm of the opinion that art isn't just creativity, it's creativity expressed; and that requires a mastery of technique. I learned that back when I was a student of the 'cello at Shenandoah Conservatory, where I learned that I didn't love it enough to master that particular body of technique - so I'd have never been any good as a 'cellist. I had all sorts of talent, in fact I got in with a paid talent scholarship. But I just wasn't willing to make the investment.

And technique really boils down to self-control. If one can control himself, he can influence how his artistic expression is made manifest. Pablo Casals learned to work the muscles in his arms, hands, and fingers in order to revolutionize the way music comes out of a 'cello. How you arrange lighting and composition in a photograph is more about you than anything else. So, yes, I'm interested in "technical" stuff about photography. I can't improve on the reality to be photographed, but I can improve how I see it and how I capture it.
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