Arcane Bloom FX (CRT)

Bloom is the glow that leaks off bright highlights - a neon sign, a lit window, a lightsaber - and it's one of those effects that's either "why does this look flat" or "why does this look like a phone filter," with not much room in between. Arcane Bloom FX is CRT's take on it: a post-process node with enough knobs to dial the glow in rather than just slapping a generic bloom overlay on top.

What it's for

It's a pure image-space post-process, dropped at the end of a pipeline after your sampler and VAE decode. Feed it a rendered image, get back the same image with a controlled glow bleeding off the bright areas. It's the kind of finishing touch that reads as "cinematic" or "stylized" depending on how hard you push it - subtle for a photoreal render, heavy for something going for a game-cinematic or fantasy-art look (the name is a nod to that aesthetic).

Where this earns its keep over a generic bloom is the threshold and smoothing controls: you can decide exactly how bright a pixel has to be before it starts glowing, and how sharp or soft that cutoff is, instead of every mid-tone bleeding into the effect.

The inputs and outputs that matter

One IMAGE in, six float widgets, one IMAGE out. The ones worth actually touching:

• threshold (default 0.65, range 0–1) - how bright a pixel needs to be before it contributes to the bloom. Lower it and more of the image starts glowing; raise it and only your brightest highlights bloom.
• intensity (default 2, range 0–4) - how strong the glow is once a pixel clears the threshold.
• smoothing (default 0.3, range 0–1) - softens the threshold cutoff so bloom fades in gradually instead of switching on hard at the edge.
• radius_multiplier (default 1, range 0.1–5) - how far the glow spreads from its source.
• saturation (default 1, range 0–2) and exposure (default 1, range 0.1–4) - color and brightness scaling applied as part of the effect.

Output is a single IMAGE, ready to save or chain into another FX node.

Installing it

Arcane Bloom FX is one of twelve nodes in CRT-Nodes' CRT/FX category (alongside Advanced Bloom FX, Film Grain FX, Lens Distort FX, and others) - a full post-processing suite bundled into PGCRT's larger CRT-Nodes pack.

ComfyUI Manager - search CRT-Nodes, install, restart.

Manual:

cd ComfyUI/custom_nodes
git clone https://github.com/PGCRT/CRT-Nodes.git
pip install -r requirements.txt

Restart ComfyUI. The FX category leans on opencv-contrib-python, scipy, and color-matcher from the pack's base requirements.txt - those are shared across all the FX nodes, not something you install per-effect.

Common issues

• Blown-out, flat-white highlights - almost always intensity set too high relative to threshold. Pull threshold up before you pull intensity down; a higher threshold with strong intensity gives punchy highlight glow without washing out the whole frame.
• Bloom looks like a haze over the entire image instead of localized glow - threshold is too low, so mid-tones are triggering the effect. This is the single most common bloom-node complaint across every pack that ships one; raise the threshold first.
• No visible effect at all - check your source image actually has bright enough pixels to clear the default 0.65 threshold. A generation that's uniformly mid-gray in exposure won't show any bloom until you lower threshold or raise exposure.
• Missing from the node list after install - CRT-Nodes keeps loading even if an optional import elsewhere in the pack fails, dropping only the affected nodes. Arcane Bloom FX depends on the pack's base opencv/scipy stack rather than anything conditional, so if it's absent, check the console for a base-requirements install problem rather than a pack-specific one.