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Can someone explains how this works? I have frustratingly been googling for 30 minutes now trying to learn how autochrome works. Being tech oriented it's so fru

by Exuma 6y ago

Can someone explains how this works? I have frustratingly been googling for 30 minutes now trying to learn how autochrome works. Being tech oriented it's so frustrating when people sum it up in 1 sentence "its made of potato starch and magically it makes color!" How does it work? Do they hand paint the screen? How does it actually add red or blue to an arbitrary shade of gray which lacks any chroma? Does it work with video too?

CrazyStat 6y ago
Autochrome was an early technique for color photography. Wikipedia has a pretty good explanation [1]. The starch grains were randomly scattered on one side of the photographic plate, and acted as filters so that small portions of the plate would capture certain colors. The plate was then developed as a positive image. When you would shine light through the developed plate it would go through the starch grains (still on the plate) as well as the developed image. The developed image controls the luminosity while the colored starch grains again act as a filter and control the hue of the transmitted light, roughly reproducing the original scene. [1] https://en.wikipedia.org/wiki/Autochrome_Lumi%C3%A8re https://en.wikipedia.org/wiki/Autochrome_Lumi%C3%A8re
- amarshall 6y ago
  > go through the starch grains (still on the plate) This part is key to understanding. The plate with the starch-based colored mosaic is not simply a filter used upon capture to be removed after (as most filters are today), but also a filter to be used upon viewing. Since the same exact “filter” is used for both capturing and viewing of a given photograph, it allows the mosaic to be random, simplifying creation of the filter.
  - jacobush 6y ago
    so... I wonder if the Bayer matrix on digital sensors was inspired by this. If each sensor was also a display, and the beyer matrix was random, it would be the same thing...
jessewmc 6y ago
What TFA is doing is basically the inverse of a digital camera sensor. They're essentially putting a coloured tint in front of each pixel (actually a block of 4 pixels) in a bayer pattern (https://en.wikipedia.org/wiki/Bayer_filter https://en.wikipedia.org/wiki/Bayer_filter), and using software to mosaic (convert) a colour image into its Bayer components if you will so that a block of four pixels under a green tint for example is lit only with it's green channel, and so on for each colour. You lose some spatial resolution this way of course.
Jetroid 6y ago
The trick is because the shade of grey DOES have chroma. You can't just apply any autochrome panel to the image (unlike what the OP is trying to do with Rainbow), instead, the negative is generated using the chrominance filter Imagine that each grain is blocking a 'pixel' of the negative. For simplicity of this explanation, I'll pretend the grains are red, green, and blue. If there's a blue grain, only blue light can get through, and thus the luminance is baked in specific to the amount of blue in that region. The same is true for the red, and the green. Thus, each 'pixel' of the negative isn't determining a monochromatic luminosity (ie black and white), but instead telling the luminosity of a single channel of red, green, or blue. When the grain filter and the developed negative are combined, we get natural colour. The same filter is used for generation and display. Another way to think of it is like this: Each pixel on our screen is actually 3 subpixels, each defining red, green, and blue, and we format our image to alternate between telling the red, green, and blue channels how bright to be. This is doing the same, but the subpixels are distributed randomly because that's much easier to make. EDIT: If you organise the grains in a geometric pattern, you get Dufaycolor[1]. [1] https://en.wikipedia.org/wiki/Dufaycolor https://en.wikipedia.org/wiki/Dufaycolor
- jacobush 6y ago
  Does it mean the filter has to very very precisely aligned when booth shooting and printing from the negative? I may be daft, and your explanation sounds reasonable but I still feel "magic + potato starch" :-D
  - CrazyStat 6y ago
    The filter is part of the photographic plate, and the plate is developed directly into a positive. So there's no alignment issue.
blattimwind 6y ago
Autochrome is pretty much just subpixels. You capture and view a greyscale image through the same dots-of-color filter plate, and thus you see color, just like an image sensor uses a Bayer filter to deconstruct color into greyscale (with three times as many pixels), and then your screen has three subpixel per pixel which you perceive as a solid color because they're sorta far away and kinda small.
- neuralRiot 6y ago
  Analog displays have no pixels but dots.

by Exuma 6y ago

CrazyStat 6y ago

Autochrome was an early technique for color photography. Wikipedia has a pretty good explanation [1]. The starch grains were randomly scattered on one side of the photographic plate, and acted as filters so that small portions of the plate would capture certain colors. The plate was then developed as a positive image. When you would shine light through the developed plate it would go through the starch grains (still on the plate) as well as the developed image. The developed image controls the luminosity while the colored starch grains again act as a filter and control the hue of the transmitted light, roughly reproducing the original scene. [1] https://en.wikipedia.org/wiki/Autochrome_Lumi%C3%A8re https://en.wikipedia.org/wiki/Autochrome_Lumi%C3%A8re

amarshall 6y ago
> go through the starch grains (still on the plate) This part is key to understanding. The plate with the starch-based colored mosaic is not simply a filter used upon capture to be removed after (as most filters are today), but also a filter to be used upon viewing. Since the same exact “filter” is used for both capturing and viewing of a given photograph, it allows the mosaic to be random, simplifying creation of the filter.
- jacobush 6y ago
  so... I wonder if the Bayer matrix on digital sensors was inspired by this. If each sensor was also a display, and the beyer matrix was random, it would be the same thing...

jessewmc 6y ago

What TFA is doing is basically the inverse of a digital camera sensor. They're essentially putting a coloured tint in front of each pixel (actually a block of 4 pixels) in a bayer pattern (https://en.wikipedia.org/wiki/Bayer_filter https://en.wikipedia.org/wiki/Bayer_filter), and using software to mosaic (convert) a colour image into its Bayer components if you will so that a block of four pixels under a green tint for example is lit only with it's green channel, and so on for each colour. You lose some spatial resolution this way of course.

Jetroid 6y ago

The trick is because the shade of grey DOES have chroma. You can't just apply any autochrome panel to the image (unlike what the OP is trying to do with Rainbow), instead, the negative is generated using the chrominance filter Imagine that each grain is blocking a 'pixel' of the negative. For simplicity of this explanation, I'll pretend the grains are red, green, and blue. If there's a blue grain, only blue light can get through, and thus the luminance is baked in specific to the amount of blue in that region. The same is true for the red, and the green. Thus, each 'pixel' of the negative isn't determining a monochromatic luminosity (ie black and white), but instead telling the luminosity of a single channel of red, green, or blue. When the grain filter and the developed negative are combined, we get natural colour. The same filter is used for generation and display. Another way to think of it is like this: Each pixel on our screen is actually 3 subpixels, each defining red, green, and blue, and we format our image to alternate between telling the red, green, and blue channels how bright to be. This is doing the same, but the subpixels are distributed randomly because that's much easier to make. EDIT: If you organise the grains in a geometric pattern, you get Dufaycolor[1]. [1] https://en.wikipedia.org/wiki/Dufaycolor https://en.wikipedia.org/wiki/Dufaycolor

jacobush 6y ago
Does it mean the filter has to very very precisely aligned when booth shooting and printing from the negative? I may be daft, and your explanation sounds reasonable but I still feel "magic + potato starch" :-D
- CrazyStat 6y ago
  The filter is part of the photographic plate, and the plate is developed directly into a positive. So there's no alignment issue.

blattimwind 6y ago

Autochrome is pretty much just subpixels. You capture and view a greyscale image through the same dots-of-color filter plate, and thus you see color, just like an image sensor uses a Bayer filter to deconstruct color into greyscale (with three times as many pixels), and then your screen has three subpixel per pixel which you perceive as a solid color because they're sorta far away and kinda small.

neuralRiot 6y ago
Analog displays have no pixels but dots.