The display technology used while the Amiga was in production was mostly based on the cathode ray tube. It was a completely analogue system.
It consisted of a glass screen that was coated with a phosphorous material. A electron beam was shot from the inside at the screen to make the phosphor glow. The beam itself was directed by bending it with electromagnetic fields. The spot that it hit would be constantly moved from left to right and top to bottom across the phosphorous screen.
The beam actually consisted of three beams with one beam per primary color (red, green and blue). But since the beams couldn't have different colors, the phosphorous screen was colored in a red, green and blue dot pattern. Each beam would only hit it's designated phoshorous areas, making it possible to mix the colors by increasing or decreasing the intensity of each beam.
The electron beams couldn't be focused precisely enough to only hit these tiny colored points. Therefore the shadow mask was placed just before the phosphorous screen. It masked out the beams, so that each electron beam would only hit its own coloured phosphorous dots. This was possible because the offset in which the electron guns were placed was inverted to the other side of the shadow mask, just like with a pinhole camera.
All these mechanisms needed to create an image on screen also led to several artefacts, that were prominent in most crt screens:
Blurry pixels
The size of a pixel was defined by the size of the area the electron beam would hit on the screen. It had to be focused to be as small as possible, but it would still be a little blurry.
Scanlines
These were the result of the electron beam scanning the screen line by line. This was also increased because computers of that time didn't usually use interlacing to increase the vertical screen resolution. They displayed 50 full screen refreshes, while televisions displayed 25 half screen refreshes (alternating between even and odd lines, resulting in visible flickering).
Shadow Mask
Just like with modern TFT panels, these are the colored dots, that the image is made of. But with CRT displays these dots were pretty big (especially with TV screens) and the dots were visible to the naked eye, if you got close enough to the screen.
Do-it-yourself CRT effect
Todays screen look very clean and blocky and sometimes it would be nice to just recreate the look of the old crt monitors.
The method I use to create the crt images is a bit complicated. But by analysing the individual artefacts it is possible to rebuild the effect in Photoshop (or any other image manipulation tool).
1. Preparation |
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We need more pixels to create the crt artefacts.
Minimum 2x the size for the scanlines.
Minimum 4x the size for the shadow mask.
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2. Blurry Pixels |
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The old crt screens (and especially the crt TVs) didn't have a crisp image resolution. By setting the blurriness after the scaling we can control the amount of blurriness better.
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3. Scanlines |
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This layer will "cut out" the horizontal lines from your image.
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4. Shadow Mask |
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This layer will add a subtle color pattern to your image that simulates the way the shadow mask creates the colored image on screen. Don't set the opacity too high, as the pattern will become irritating to the eye and it will take away too much brightness from the image.
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5. Finalize |
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All the effects that we applied make the image darker. It is therefore necessary to lighten up the image, even if it means that individual details will be burned out.
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