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Ok, but that’s not what an digital image is. Images are designed to be invariant across camera capture and display hardware. The panel driver should interpret t

Ok, but that’s not what an digital image is. Images are designed to be invariant across camera capture and display hardware. The panel driver should interpret the dsp representation into an appropriate electronic pixel output.

fluoridation 1y ago
Well, "what a digital image is" is a sequence of numbers. There's no single correct way to interpret the numbers, it depends on what you want to accomplish. If your digital image is a representation of, say, the dead components in an array of sensors, the signal processing theoretic interpretation of samples may not be useful as far as figuring out which sensors you should replace.
- grandempire 1y ago
  > There's no single correct way to interpret the numbers They are just bits in a computer. But there is a correct way of to interpret them in a particular context. For example 32 bits can be meaningless - or it can have an interpretation as a twos complement integer which is well defined. If you are looking to understand how an operating system will display images, or how graphics drivers work, or how photoshop will edit them, or what digital cameras produce, then it’s the point sample definition.
  - Dylan16807 1y ago
    Cameras don't take point samples. That's an approximation, just as inaccurate as a rectangle approximation. And for pixel art, the intent is usually far from points on a smooth color territory. Multiple interpretations matter within different contexts inside the computer context.
    - grandempire 1y ago
      > Cameras don't take point samples. That's an approximation They use a physical process to attempt to determine light at a single point. That’s their model they try to approximate. > And for pixel art, the intent is usually far from points on a smooth color territory. And notice that to display pixel art you need to tell it to interpret the image data differently. Also it has a vastly different appearance on a CRT where it was designed which is less like a rectangle.
      - Dylan16807 1y ago
        > They use a physical process to attempt to determine light at a single point. That’s their model they try to approximate. According to who? A naked camera sensor with lens sure doesn't do that, it collects squares of light, usually in a mosaic of different colors. Any point approximation would have to be in software.
        grandempire 1y ago
        Yep, cameras filter the input from sensors. > Any point approximation would have to be in software. Circuits can process signals too.
        Dylan16807 1y ago
        They usually do, but their software decisions are not gospel. They don't change the nature of the underlying sensor, which grabs areas that are pretty square.
        grandempire 1y ago
        > which grabs areas And outputs what? Just because the input is an area does not mean the output is an area. What it if it outputs the peak of the distribution across the area? > that are pretty square. If we look at a camera sensor and do not see a uniform grid of packed area elements would that convince you? I notice you haven’t shared any criticism of the point model - widely understood by the field.
        Dylan16807 1y ago
        > And outputs what? Just because the input is an area does not mean the output is an area. > What it if it outputs the peak of the distribution across the area? It outputs a voltage proportional to the (filtered) photon count across the entire area. > If we look at a camera sensor and do not see a uniform grid of packed area elements would that convince you? Non-uniformity won't convince me points are a better fit, but if the median camera doesn't use a grid I'll be interested in what you have to show. > I notice you haven’t shared any criticism of the point model - widely understood by the field. This whole comment line is a criticism of the input being modeled as points, and my criticism of the output is implied by my pixel art comment above (because point-like upscaling causes a giant blur) and also exists in other comments like this one: https://news.ycombinator.com/item?id=43777957 https://news.ycombinator.com/item?id=43777957
glitchc 1y ago
Yeah but the article is about a pixel, which has different meanings. Making blanket statements is not helpful in resolving definitions. Truth is, a pixel is both a sample and a transducer. And in transduction, a pixel is both an integrator and an emitter.
- grandempire 1y ago
  I’ll quote my other comment: > If you are looking to understand how your operating system will display images, or how your graphics drivers work, or how photoshop will edit them, or what digital cameras aim to produce, then it’s the point sample definition.
  - tobr 1y ago
    Sometimes yes. Sometimes no! There are certainly situations where a pixel will be scaled, displayed, edited or otherwise treated as a little square.
    - seba_dos1 1y ago
      A little rectangle even.
      - grandempire 1y ago
        What is a little rectangle? Physical display pixels are separate RGB leds with a non-rectangular shape.
        Dylan16807 1y ago
        They're rectangles on my monitor.
        cma 1y ago
        If black and white or some other cases, but there are typically subpixels that can make things like sparse enough text stroke transitions get 3X horizontal resolution.
kjkjadksj 1y ago
Well the camera sensor captures a greater dynamic range than the display or print media or perhaps even your eyes, so something has to give. If you ever worked with a linear file without gamma correction you will understand what I mean.
- grandempire 1y ago
  And that full dynamic range is in the images’s point samples, ready to be remapped for a physical output.
pornel 1y ago
We commonly use hardware like LCDs and printers that render a sharp transition between pixels without the Gibbs' phenomenon. CRT scanlines were close to an actual 1D signal (but not directly controlled by the pixels, which the video cards still tried to make square-ish), but AFAIK we've never had a display that is a 2D signal that we assume in image processing. In signal processing you have a finite number of samples of an infinitely precise contiguous signal, but in image processing you have a discrete representation mapped to a discrete output. It's contiguous only when you choose to model it that way. Discrete → contiguous → discrete conversion is a useful tool in some cases, but it's not the whole story. There are images designed for very specific hardware, like sprites for CRT monitors, or font glyphs rendered for LCD subpixels. More generally, nearly all bitmap graphics assumes that pixel alignment is meaningful (and that has been true even in the CRT era before the pixel grid could be aligned with the display's subpixels). Boxes and line widths, especially in GUIs, tend to be designed for integer multiples of pixels. Fonts have/had hinting for aligning to the pixel grid. Lack of grid alignment, an equivalent of a phase shift that wouldn't matter in pure signal processing, is visually quite noticeable at resolutions where the hardware pixels are little squares to the naked eye.
- grandempire 1y ago
  I think you are saying there are other kinds of displays which are not typical monitors and those displays show different kinds of images - and I don’t disagree.
  - pornel 1y ago
    I'm saying "digital images" are captured by and created for hardware that has the "little squares". This defines what their pixels really are. Pixels in these digital images actually represent discrete units, and not infinitesimal samples of waveforms. Since the pixels never were a waveform, never were sampled from such signal (even light in camera sensors isn't sampled along these axis), and don't get displayed as a 2D waveform, the pixels-as-points model from the article at the top of this thread is just an arbitrary abstract model, but it's not an accurate representation of what pixels are.
nextaccountic 1y ago
That's only for images coming directly from a camera. If the images were generated in another way, the idea that a pixel is a little square is sometimes ok (example, pixel art)

fluoridation 1y ago

Well, "what a digital image is" is a sequence of numbers. There's no single correct way to interpret the numbers, it depends on what you want to accomplish. If your digital image is a representation of, say, the dead components in an array of sensors, the signal processing theoretic interpretation of samples may not be useful as far as figuring out which sensors you should replace.

grandempire 1y ago
> There's no single correct way to interpret the numbers They are just bits in a computer. But there is a correct way of to interpret them in a particular context. For example 32 bits can be meaningless - or it can have an interpretation as a twos complement integer which is well defined. If you are looking to understand how an operating system will display images, or how graphics drivers work, or how photoshop will edit them, or what digital cameras produce, then it’s the point sample definition.
- Dylan16807 1y ago
  Cameras don't take point samples. That's an approximation, just as inaccurate as a rectangle approximation. And for pixel art, the intent is usually far from points on a smooth color territory. Multiple interpretations matter within different contexts inside the computer context.
  - grandempire 1y ago
    > Cameras don't take point samples. That's an approximation They use a physical process to attempt to determine light at a single point. That’s their model they try to approximate. > And for pixel art, the intent is usually far from points on a smooth color territory. And notice that to display pixel art you need to tell it to interpret the image data differently. Also it has a vastly different appearance on a CRT where it was designed which is less like a rectangle.
    - Dylan16807 1y ago
      > They use a physical process to attempt to determine light at a single point. That’s their model they try to approximate. According to who? A naked camera sensor with lens sure doesn't do that, it collects squares of light, usually in a mosaic of different colors. Any point approximation would have to be in software.
      - grandempire 1y ago
        Yep, cameras filter the input from sensors. > Any point approximation would have to be in software. Circuits can process signals too.
        Dylan16807 1y ago
        They usually do, but their software decisions are not gospel. They don't change the nature of the underlying sensor, which grabs areas that are pretty square.
        grandempire 1y ago
        > which grabs areas And outputs what? Just because the input is an area does not mean the output is an area. What it if it outputs the peak of the distribution across the area? > that are pretty square. If we look at a camera sensor and do not see a uniform grid of packed area elements would that convince you? I notice you haven’t shared any criticism of the point model - widely understood by the field.
        Dylan16807 1y ago
        > And outputs what? Just because the input is an area does not mean the output is an area. > What it if it outputs the peak of the distribution across the area? It outputs a voltage proportional to the (filtered) photon count across the entire area. > If we look at a camera sensor and do not see a uniform grid of packed area elements would that convince you? Non-uniformity won't convince me points are a better fit, but if the median camera doesn't use a grid I'll be interested in what you have to show. > I notice you haven’t shared any criticism of the point model - widely understood by the field. This whole comment line is a criticism of the input being modeled as points, and my criticism of the output is implied by my pixel art comment above (because point-like upscaling causes a giant blur) and also exists in other comments like this one: https://news.ycombinator.com/item?id=43777957 https://news.ycombinator.com/item?id=43777957

glitchc 1y ago

Yeah but the article is about a pixel, which has different meanings. Making blanket statements is not helpful in resolving definitions. Truth is, a pixel is both a sample and a transducer. And in transduction, a pixel is both an integrator and an emitter.

grandempire 1y ago
I’ll quote my other comment: > If you are looking to understand how your operating system will display images, or how your graphics drivers work, or how photoshop will edit them, or what digital cameras aim to produce, then it’s the point sample definition.
- tobr 1y ago
  Sometimes yes. Sometimes no! There are certainly situations where a pixel will be scaled, displayed, edited or otherwise treated as a little square.
  - seba_dos1 1y ago
    A little rectangle even.
    - grandempire 1y ago
      What is a little rectangle? Physical display pixels are separate RGB leds with a non-rectangular shape.
      - Dylan16807 1y ago
        They're rectangles on my monitor.
        cma 1y ago
        If black and white or some other cases, but there are typically subpixels that can make things like sparse enough text stroke transitions get 3X horizontal resolution.

kjkjadksj 1y ago

Well the camera sensor captures a greater dynamic range than the display or print media or perhaps even your eyes, so something has to give. If you ever worked with a linear file without gamma correction you will understand what I mean.

grandempire 1y ago
And that full dynamic range is in the images’s point samples, ready to be remapped for a physical output.

pornel 1y ago

We commonly use hardware like LCDs and printers that render a sharp transition between pixels without the Gibbs' phenomenon. CRT scanlines were close to an actual 1D signal (but not directly controlled by the pixels, which the video cards still tried to make square-ish), but AFAIK we've never had a display that is a 2D signal that we assume in image processing. In signal processing you have a finite number of samples of an infinitely precise contiguous signal, but in image processing you have a discrete representation mapped to a discrete output. It's contiguous only when you choose to model it that way. Discrete → contiguous → discrete conversion is a useful tool in some cases, but it's not the whole story. There are images designed for very specific hardware, like sprites for CRT monitors, or font glyphs rendered for LCD subpixels. More generally, nearly all bitmap graphics assumes that pixel alignment is meaningful (and that has been true even in the CRT era before the pixel grid could be aligned with the display's subpixels). Boxes and line widths, especially in GUIs, tend to be designed for integer multiples of pixels. Fonts have/had hinting for aligning to the pixel grid. Lack of grid alignment, an equivalent of a phase shift that wouldn't matter in pure signal processing, is visually quite noticeable at resolutions where the hardware pixels are little squares to the naked eye.

grandempire 1y ago
I think you are saying there are other kinds of displays which are not typical monitors and those displays show different kinds of images - and I don’t disagree.
- pornel 1y ago
  I'm saying "digital images" are captured by and created for hardware that has the "little squares". This defines what their pixels really are. Pixels in these digital images actually represent discrete units, and not infinitesimal samples of waveforms. Since the pixels never were a waveform, never were sampled from such signal (even light in camera sensors isn't sampled along these axis), and don't get displayed as a 2D waveform, the pixels-as-points model from the article at the top of this thread is just an arbitrary abstract model, but it's not an accurate representation of what pixels are.

nextaccountic 1y ago

That's only for images coming directly from a camera. If the images were generated in another way, the idea that a pixel is a little square is sometimes ok (example, pixel art)