11–20 of 68 posts
> Dithering a black-to-white gradient will be wrong without linearising first. TBH both look wrong to me. If I squint, neither dithering patterns match the original gradient... but the non-linearized one looks the most similar. What could be causing this?
Hypercorrection, in this care over-linearisation.
They may not want to imply that didder's linearized rabbit is wrong, but I'm comfortable saying so. It's not just a little dark, it's way dark, to the point of hiding detail. The linearized RGB palette is similarly awful. It clobbers a whole swath of colors, rendering them as nearly black. Purples are particularly brutalized. Yellows disappeared and became white. On my phone, the middle palette doesn't appear too bri…
Others suggest that the error is using the wrong metric for choosing the closest color, but I disagree. That wouldn't such drastic systematic darkening like this, as the palette is probably still pretty dense in the RGB cube.
Where the linearisation really matters is the arithmetic for the error diffusion, you definitely want to diffuse the error in a linear colorspace, and you are free to choose a good perceptual space for choosing the closest color at each pixel, but calculate the error in a linear space.
Visual perception is weird. But when you squint your eyes to blur the image, you are definitely mixing in a linear colorspace, as that's physical mixing of light intensities before the light even reaches your retina. So you have to match that when diffusing the error.
edit:
It also doesn't help that most (all?) browsers do color mixing wrong when the images are scaled, so if you don't view the dithered images at 100% without DPI scaling than you might get significantly distorted colors due to that too.
edit2:
For comparison this is what imageworsener does:
You really need to open the image in a viewer where each image pixel is exactly one device pixel large, otherwise the color arithmetic used for scaling by viewers is of variable quality (often very poor).
Seems that at some level it should, though perhaps not directly at the pixel level due to the high frequency of the per-pixel differences, but maybe at the more coarse "averaged" level?
One of those things I've wanted to explore but remains on my to-do list...
> Dithering a black-to-white gradient will be wrong without linearising first. TBH both look wrong to me. If I squint, neither dithering patterns match the original gradient... but the non-linearized one looks the most similar. What could be causing this?
edit:
Reading back, viewing the gradients also not at 100% zoom level could also itself cause the mismatch, because browsers just suck at image scaling.
> Dithering a black-to-white gradient will be wrong without linearising first. TBH both look wrong to me. If I squint, neither dithering patterns match the original gradient... but the non-linearized one looks the most similar. What could be causing this?
They have a different default gamma and they may show a different gray level.
(It bite me a long time ago. I made a gif that has the same RGB bacground than a webpage. In my pc it was fine, but in a mac they the border was very visible and the result horrible. My solution was to change the backgroung of the webpage from a RGB number to a 1 pixel gif with repetition or scale to fill the page.)
This was nearly eight years ago, but I managed to find it this morning and uploaded it to YouTube.
Here was the resulting animation: https://youtu.be/FHrIQOWeerg
I remember I used Processing to build it, and it took so long to animate as I had to export it frame-by-frame. Fun days!
> Dithering a black-to-white gradient will be wrong without linearising first. TBH both look wrong to me. If I squint, neither dithering patterns match the original gradient... but the non-linearized one looks the most similar. What could be causing this?
See: Dithering should happen in sRGB https://www.shadertoy.com/view/NssBRX
They may not want to imply that didder's linearized rabbit is wrong, but I'm comfortable saying so. It's not just a little dark, it's way dark, to the point of hiding detail. The linearized RGB palette is similarly awful. It clobbers a whole swath of colors, rendering them as nearly black. Purples are particularly brutalized. Yellows disappeared and became white. On my phone, the middle palette doesn't appear too bri…
The dithered gradient shouldn't be pure black halfway through.
> Dithering a black-to-white gradient will be wrong without linearising first. TBH both look wrong to me. If I squint, neither dithering patterns match the original gradient... but the non-linearized one looks the most similar. What could be causing this?
I remember I had quite a bit of discussion with madshi when MadVR tried implementing it. You can do something that comes close by modifying the colour space into something that is gamma light in the integer part and linear light in the fractional part.
If the value of a pixel is x you then get something like floor(x) + (l - ginv(x)) / (l - u) with l and u the the two shades corresponding to floor(x) and ceil(x) in linear light.
Though technically error diffusion will still be incorrect, but it does handle constant shades correctly and most alternatives are worse somehow.
If anyone thinks their websites are too colorful, I made a pure JavaScript web component to dither images on client in real time, taking into account the real pixel size of the current display.
https://sheep.horse/2023/1/improved_web_component_for_pixel-...