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A Pixel Is Not A Little Square (1995) [pdf]

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Re: A Pixel Is Not A Little Square (1995) [pdf]

#41

Post by glowcoil »

raphlinus wrote: post #39
glowcoil wrote: post #37

Earlier quoted context omitted.

As a simple demonstration, here's an image of a 1px white-on-black line and a 1px black-on-white line: https://imgur.com/a/9d9Tu3x It's axis-aligned and box-filtered so there are no shades of gray, which means gamma is irrelevant. The white-on-black line appears to have a greater thickness than the black-on-white line. There's a lot of empirical research showing that reading performance is better with positive-polari…

One caveat, if viewing this image on a high-dpi display there will be blurring from image upsampling by the browser. My eyes have the same result as yours: the white line appears thicker than the black one. Here's the interesting thing about your observation: doing alpha compositing of text in a perceptual space (as opposed to a linear space) results in a thickening of black-on-white and a thinning of white-on-black.…

I don't think they actually take luminance into account (although I personally like the idea); I just meant that they solve the problem of "black-on-white text looks too thin" by thickening the text, rather than messing up other parts of the pipeline.

Re: A Pixel Is Not A Little Square (1995) [pdf]

#42

Post by Someone »

raphlinus wrote: post #3

I imagine this came up partly as a result of the recent alpha compositing discussion. We desperately need some research, based in user studies and using modern display technology, to settle some basic questions: * What reconstruction filter gives the best results? Is it the same for vector (text) and natural images? By "best" I do mean contrast (sharpness) and lack of visible artifacts. * For rendering of very thin l…

There likely is tons of research on this in psychophysics (https://en.wikipedia.org/wiki/Psychophysics). I’m not familiar with it, but I do know that you’ll find that it isn’t as simple as what you state. For example, Google gave me http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.108.... I don’t know whether it’s good, or when it was written.

The perception of equal line thickness may depend on orientation of the lines (https://res.mdpi.com/vision/vision-03-00001/article_deploy/v...), distance from the fovea, distance from where your attention lies (a can of worms even deeper. I don’t think there’s agreement on whether one can attend to more than one visual location at a time, or what ‘attention’ even is), direction of those distances (vertical will almost certainly be different from horizontal, sight could be better or worse in the nasal direction vs the temporal one), light/dark adaptation of the eyes, whether subjects are color-blind, etc.

I fear that, to qet something that’s better than Weber’s law (https://en.wikipedia.org/wiki/Weber–Fechner_law), you need a model so complex that it doesn’t make sense to start using it.

Re: A Pixel Is Not A Little Square (1995) [pdf]

#43

Post by pornel »

However, image is not a wave. Sampling theorem applies beautifully to audio, but only to a limited degree to images. Some filters make sense in frequency domain, eyes are sensitive to certain frequencies more than others, but it all breaks down on hard edges, which don't behave like square waves.

The problem is that in images the Gibb's effect is visible and annoying (ringing artifact). If sampling theorem applied, people wouldn't be able to see it, like they can't hear the difference between square waves shifted by a half of a sample.

Re: A Pixel Is Not A Little Square (1995) [pdf]

#44

Post by raphlinus »

glowcoil wrote: post #41
raphlinus wrote: post #39

Earlier quoted context omitted.

One caveat, if viewing this image on a high-dpi display there will be blurring from image upsampling by the browser. My eyes have the same result as yours: the white line appears thicker than the black one. Here's the interesting thing about your observation: doing alpha compositing of text in a perceptual space (as opposed to a linear space) results in a thickening of black-on-white and a thinning of white-on-black.…

I don't think they actually take luminance into account (although I personally like the idea); I just meant that they solve the problem of "black-on-white text looks too thin" by thickening the text, rather than messing up other parts of the pipeline.

Absolutely, and I think there's a very strong case to be made for that. One of the points I'm trying to make is that you have to solve it somewhere. People who focus narrowly on "correct gamma" often miss this, especially when "incorrect gamma" is also plausibly a workable solution.

Re: A Pixel Is Not A Little Square (1995) [pdf]

#45

Post by mhh__ »

want2know wrote: post #25

The same is true for digital audio. We are so used to see the visual presentation of samples that look like a bar diagram, that a lot of people think analog sounds better because the curves are smoother. Chris Montgomery has a great talk about this.

https://xiph.org/video/vid2.shtml The talk

https://youtu.be/cIQ9IXSUzuM I wish I could force any audiophiles to watch it before they waste their money on snake oil. I think a similar point can be made about analogue synthesis, e.g. You pay Moog £1500 for what is ultimately a fancy box for a relatively simple analogue circuit.

Re: A Pixel Is Not A Little Square (1995) [pdf]

#46

Post by egypturnash »

blevin wrote: post #38
dahart wrote: post #36

Earlier quoted context omitted.

There were a variety of widths, it was one axis of the study. But I don’t remember the details, it is certainly possible you’re talking about something we didn’t test. Personally, at first I couldn’t even see the differences they were discussing. Having studied graphics and signal processing for a few years in graduate school before that job, I thought I would be good at seeing the differences, and I was a bit shocke…

My experience has likewise been that film DP’s have extremely impressive visual acuity, memory for color, etc. Talented artists often have developed whole sets of skills that the rest of us are unaware are even skills. In the same way a programmer might have thought about cache line false sharing as it affects memory hierarchy throughput, visual art often hides lots of expertise you cannot directly perceive, even as…

I like to describe “learning to draw” as “installing a 3d modeling and rendering package on your brain, along with a decent collection of base models to modify”. It’s a complex skill set. If you start animating you get to add in a physics simulation. And you become conscious of so many little things that the layman only notices when you get it wrong.

Re: A Pixel Is Not A Little Square (1995) [pdf]

#47

Post by justanothersys »

bjourne wrote: post #26

A pixel is a picture element. An element of a picture. Hence the name... It turns out that thinking of them as little boxes arranged in rectangular grids is very useful. Because that is how computers deal with them. Not as point samples. The article reminds me of the many mathematical text I've read insisting on that vectors are not tuples of numbers. That thinking of them as anything other than directions with magni…

But how will your students learn to think outside the little boxes?

Re: A Pixel Is Not A Little Square (1995) [pdf]

#48

Post by raphlinus »

Someone wrote: post #42
raphlinus wrote: post #3

I imagine this came up partly as a result of the recent alpha compositing discussion. We desperately need some research, based in user studies and using modern display technology, to settle some basic questions: * What reconstruction filter gives the best results? Is it the same for vector (text) and natural images? By "best" I do mean contrast (sharpness) and lack of visible artifacts. * For rendering of very thin l…

There likely is tons of research on this in psychophysics ( https://en.wikipedia.org/wiki/Psychophysics ). I’m not familiar with it, but I do know that you’ll find that it isn’t as simple as what you state. For example, Google gave me http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.108... . I don’t know whether it’s good, or when it was written. The perception of equal line thickness may depend on orientatio…

It's possible this research has been done, but if so I haven't seen it yet. Basically the reason I feel confident asserting it is that I'm talking very specifically about the stimulus produced by modern displays. I know there's some work by Avi Naiman on CRT displays from the very early 90's[0]. There might be some other work done on low-resolution LCD's, but even aside from resolution it's only modern, high quality displays that have good contrast and low dependence on viewing angle (which affects gamma greatly).

Another place to look is Kevin Larson's work on subpixel rendering, which informed Microsoft's ClearType efforts. But that was done mostly around 10 years ago, when displays also were different. A good representative is [1].

Here's another pretty good paper I found[2], but it focuses more on the display technology than the perception side.

So what I'm looking for is adjacent to general psychophysics results on visual perception, but much more specific to what real displays do. That literature is pretty thin on the ground.

[0]: Avi C. Naiman and Walter Makous. Spatial nonlinearities of gray-scale CRT pixels, 1992

[1]: https://www.researchgate.net/publication/264485766_Optimizin...

[2]: https://pdfs.semanticscholar.org/8fc4/ecc59380f24e363c6a5d6a...

Re: A Pixel Is Not A Little Square (1995) [pdf]

#49

Post by jacobolus »

raphlinus wrote: post #48
Someone wrote: post #42

Earlier quoted context omitted.

There likely is tons of research on this in psychophysics ( https://en.wikipedia.org/wiki/Psychophysics ). I’m not familiar with it, but I do know that you’ll find that it isn’t as simple as what you state. For example, Google gave me http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.108... . I don’t know whether it’s good, or when it was written. The perception of equal line thickness may depend on orientatio…

It's possible this research has been done, but if so I haven't seen it yet. Basically the reason I feel confident asserting it is that I'm talking very specifically about the stimulus produced by modern displays. I know there's some work by Avi Naiman on CRT displays from the very early 90's[0]. There might be some other work done on low-resolution LCD's, but even aside from resolution it's only modern, high quality…

There is research about perception of physically printed lines, done by e.g. print photography companies decades ago.

There is plenty of formal signal processing analysis of the aliasing artifacts at different angles created by grids of pixels.

The ImageMagick folks did a bunch of experimentation about resampling filters as used in arbitrary transformations of existing raster images. https://www.imagemagick.org/Usage/filter/nicolas/ – of course what looks best depends significantly on (subjective) preferences and on what the source image is.

Re: A Pixel Is Not A Little Square (1995) [pdf]

#50

Post by kazinator »

Pixel and voxel are not commensurable. A pixel is a display hardware concept. A voxel is more comparable to a texel.

https://en.wikipedia.org/wiki/Texel_(graphics)

Texels and Voxels can be square/cubic, such as in video game applications where it is accepted and exploited as a fundamental esthetic: worlds are textured with tiled mosaics which reveal their square unit when approached closely, and ditto for worlds made of voxels.

A voxel as a sample of a solid, for instance from a computed tomography, where the fidelity of the reconstruction matters, is subject to different requirements.

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