Invert with light green produces muddy brown colours in beta branch

[edwardhorsford]

I quite like the invert with light green option. Alas it seems to be broken in the beta branch with my test pdf. Most lines come out a muddy brown - where they display fine in the main branch.

I believe I have traced it (via Claude) to the fix in #402.

Beta branch

0px line weight	1px line weight

Main branch

0px line weight	1px line weight

I suspect this is related to the source data not being 100% black, but some shade of grey - unless over some threshold value it's not enough to get saturated?

Besides looking again at the fix in #402, I wonder about applying some kind of level/threshold filter so pixels over x% darkness are darkened even further? You'd lose shading in pdfs, but gain more contrast. I suspect that's probably a good tradeoff for patterns.

[courtneypattison]

Good catch! You're correct I was trying to fix #402 and introduced the muddy brown. I made a mental note to fix it before the next release but didn't reopen the bug. Apologies.

I wonder about applying some kind of level/threshold filter so pixels over x% darkness are darkened even further? You'd lose shading in pdfs, but gain more contrast. I suspect that's probably a good tradeoff for patterns.

That's definitely worth a try. I'm open to any changes that would get us to bright green for both PDFs and SVGs.

[edwardhorsford]

@courtneypattison I had a go improving the image quality in this PR and also some other ui fixes to improve the general responsiveness - such as caching image data for each line weight so if you swap between them it's faster after first render. I've touched a lot of files so you probably wouldn't want my direct pr, but the code might be of interest. I suspect first load of safari is probably slower, but at a benefit of better image quality after load.

[edwardhorsford]

@courtneypattison My fork has now diverged significantly, but I've reworked how colours get applied and am pleased with the solution. It's part of this PR that also contains other ui fixes - hopefully the PR description is helpful (LLM written).

I have a two stage fix:

• A filter called 'push darks' that pushes most grey shades to black so we end up with more black lines rather than grey. The erosion step has an annoying byproduct of turning thin black lines grey, so this counteracts that. You could also think of it as a threshold filter making most contrasty things black.
• A recolour filter that acts to convert black to a specific chosen theme colour. The inspiration was taken from this Stackoverflow thread. As this produces the exact target colour, it's also easy to add adjustments to make it lighter or darker. Any shades of grey in the source artwork get recoloured but will naturally be darker.

[courtneypattison]

@edwardhorsford thank you so much for sharing and I'm sorry for being so unresponsive.