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Show HN: Make images render brighter than white by abusing Rec.2100 PQ profiles
12 days ago
- SDR white (about 200 nits) is not a display's maximum brightness; HDR-capable panels can output 1,000–1,600 nits, leaving headroom.
- A Rec.2100 PQ color profile embedded in an 8-bit JPEG tricks color-managed renderers into displaying bright values in this headroom, making images glow brighter than the interface.
- Platforms like LinkedIn preserve ICC profiles through re-encoding, allowing the technique to work, though it fails with screenshots, re-saving, or compression.
- Superwhite properly processes images per pixel: decoding sRGB to linear light, converting primaries, masking white regions, boosting brightness, and encoding with PQ.
- The technique is a novelty with limited lifespan, as platforms may clamp brightness like they did for HDR video; subtle use is recommended for best effect.
Revisiting Yliluoma's ordered dither algorithm
9 days ago
- The article explores Joel Yliluoma's 2011 ordered dither algorithm and introduces simplified EMA variants.
- It compares these methods to Thomas Knoll's Photoshop dither algorithm, focusing on color selection for palette-based images.
- The EMA variants use exponential moving averages to pick candidate colors, with options for exact or constant mixing factors.
- Knoll's algorithm remains faster due to O(N log K) complexity, while Yliluoma-2 and EMA variants are O(NK).
- Dither quality depends on candidate count N and mixing factor t, with N around 2K recommended for K-color images.
- Source code is provided for implementations including Knoll, EMA, and offset dithers.
My Images Are Dithered
11 hours ago
- Dithering reduces file size by using fewer colors while maintaining detail, and gives a cool aesthetic.
- The author uses ImageMagick's 'convert' command to simulate AM (amplitude-modulated) printing dots.
- The process involves converting to CMYK, separating channels, creating dot grids, rotating them at specific angles, and overlaying.
- Limiting each channel to 2 colors before combining produces a more accurate halftone effect.
- The old method limited the palette to monochrome (black and pink), while the new method uses a remap to a pink palette for more depth.
- The method is computationally expensive and not optimal for file size reduction, but achieves a distinctive print-like look.
- The script automates the process for multiple images, but the author notes it's not true dithering and can take 10 seconds per image.

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#image processing

Show HN: Make images render brighter than white by abusing Rec.2100 PQ profiles

Revisiting Yliluoma's ordered dither algorithm

My Images Are Dithered