How to Upscale Anime Video Without Soft, Grey Lines

Anime fails differently from live action

When I first ran cartoon footage through my video upscaler, the picture got bigger and cleaner, but something felt off. The colors were fine. The lines were the problem. The thin dark outlines that give anime its look had turned a little soft and a little grey.

That makes sense once you compare how the two kinds of footage are made. A camera shot is full of soft gradients, skin texture and sensor noise, so a slightly soft edge looks natural. A cel-animated frame is mostly flat color held together by thin, dark line art. Viewers judge anime quality almost entirely by those lines. When they are crisp and black, a 480p episode can look clean on a big screen. When they are fuzzy and grey, even a 1080p rip looks washed out.

What goes wrong with a general upscaler

The AI model in my tool, IMDN, learned from photographs. When it rebuilds an edge, it rebuilds it the way a photo edge usually looks: slightly soft, with a smooth transition between the two sides. Applied to anime, that turns a solid black stroke into a dark grey one with blurry borders.

The obvious fix is to sharpen the result, and that makes a different problem. Ordinary sharpening adds a bright and a dark halo around every edge. On a busy photo you barely notice it. On flat anime colors, a glowing outline around every stroke is easy to spot and looks worse than the blur it replaced.

So anime needs something between "soft" and "haloed": edges that get steeper without overshooting, and lines that get darker without the whole frame getting a sticker outline.

What a line-art pass does

I added an Anime / cartoon option that runs after the upscale and treats each frame as line art. It works on brightness only, so it never adds color fringes. It does three things:

• It deblurs edges without halos. The pass sharpens, then limits every pixel to the brightest and darkest values already around it. Edges get steeper, but they cannot glow or ring.
• It darkens real lines only. The pass picks out dark strokes thinner than a small window and deepens them. A plain edge between two colored areas, like a white shirt against a wall, does not get a fake outline.
• It thins lines back down. Upscaling makes every stroke fatter along with the frame. A line that was 2 pixels wide in the source is 4 pixels wide after 2x and 8 after 4x. The pass pulls pixels away from line centers, so the lines look drawn at the new resolution instead of stretched.

Every step scales with the upscale factor, which is why the settings that work at 2x do not need adjusting at 4x. On videos 720p and smaller, the pass runs right after the AI model. On larger videos it replaces FSR's own sharpening step, because it does a cleaner job on line art. If you want the background on that engine, I wrote about what FSR is and how it works.

How to upscale an anime video

The anime pass needs WebGPU, so use a recent version of Chrome. On the CPU fallback the checkbox has no effect. In my own tests Chrome also ran clearly faster than Firefox on the same file. For a long episode, I suggest testing a few seconds first, because the slider tells you whether the result is worth waiting for.

Which scale to pick for which source

The output size is always your source resolution multiplied by the scale. These are the cases anime fans ask about most:

Old DVD anime at 480p is the classic case. Use 2x for a quick lift. Use 4x if you want it at 1080p or above on a TV, and expect a bigger file and a longer wait.

A 720p episode at 2x gives you 1440p, which plays on any Full HD screen and looks sharper than a plain 1080p copy.

A 1080p episode to 4K takes 2x on the FSR path with anime mode on. That path is fast and keeps lines sharp at 3840×2160. I would not take 1080p to 8K. The file gets huge and the visible gain is small.

What upscaling cannot fix

An upscaler adds pixels and rebuilds edges. It does not repair what the source file lost. A low-bitrate rip with blocky color areas and banding in the gradients will show the same blocks and bands, only bigger. If an episode looks bad because it was compressed hard, use the best copy you can find before you upscale. The tool also keeps the original frame rate, so choppy footage stays choppy.

If you are not sure whether your video has a resolution problem or a different one, this guide to blurry video sorts the causes, and I explain what upscaling can and cannot recover in does video upscaling actually work.

It works on more than anime

The pass treats any flat-color art the same way, so I use it for Western cartoons, 2D game footage, animated explainers and motion graphics too. Leave it off for live action. On real footage the line-darkening turns hair, wrinkles and shadows into drawn-looking strokes.

Other tools are worth knowing about

Dedicated anime upscalers exist, and some are very good. Programs like waifu2x and Real-ESRGAN with its anime model run on a desktop GPU, and Anime4K applies a real-time shader while you watch. With a strong graphics card and some patience, those can beat what a browser tool does. I built mine to run on the device you already have, in a browser tab, without installing anything, and I accept that trade.

Upscale first, compress second

Upscaling makes the file bigger. If the result is too large to share, run it through the video compressor afterwards. Upscale first and compress second, never the other way round, because compressing first throws away detail the upscaler could have used.

Try it on your own episode

My video upscaler runs in your browser on your own graphics card and shows a before/after slider when it finishes. Tick Anime / cartoon, try 2x on a short clip, and look at the lines on a close-up. If you are working with GIFs instead, the GIF upscaler uses the same model.