RGBA Save (Swwan)

ComfyUI's built-in Save Image throws away alpha, full stop. If you've ever cut out a subject, done a clean pass, and then watched the exported PNG come out on a black background, you know exactly what this node is for. RGBA_Save is the pack's dedicated transparent-PNG writer: it takes the RGB and the alpha mask separately and combines them into a real RGBA file.

It's deliberately single-purpose. No JPEG, no WebP, no format switching - you want this node when the output must be a transparent PNG, and you use the pack's RGBA_Multi_Save when you need to flip formats. That narrowness is a feature: one less thing to misconfigure.

Where it sits in the workflow

It's the terminal node of the pack's transparency pipeline:

Load Image → RGBA Safe Pre → (RGB-only nodes) → RGBA Safe Post → RGBA Save

RGBA_Safe_Pre premultiplies your RGB (so intermediate nodes don't smear fringes into the image), and RGBA_Safe_Post restores straight color and resizes the alpha. RGBA_Save then merges the corrected RGB with that alpha into the PNG. If you feed it premultiplied RGB directly, the saved file will look too dark at semi-transparent edges - that's the tooltip's warning in action: use RGBA_Safe_Post first if the image is still premultiplied.

Inputs

Three inputs, and you already have all of them if you followed the pipeline:

• image (IMAGE) - the RGB to save, ideally the image_out from RGBA_Safe_Post.
• alpha (MASK) - the alpha to embed, ideally the alpha_out from Post. If its resolution doesn't match the image, the node resizes it to fit, so mismatched sizes don't crash it.
• filename_prefix (STRING, default "RGBA") - the prefix for the saved files. Files land in ComfyUI's output/ folder with the standard prefix_counter.png naming.

How it works

Under the hood it does the boring-but-important bookkeeping you expect from a save node: it resolves the output path, stacks the RGB and alpha into an RGBA array, and writes it with PIL. It also embeds the workflow/prompt metadata into the PNG like ComfyUI's normal save does (unless you run ComfyUI with metadata disabled), so the file stays portable and re-loadable. png_compress_level is fixed at 4 - you won't find a quality knob here, which is fine; PNG's lossless anyway.

Install

It ships in ComfyUI_Swwan. ComfyUI Manager → search "ComfyUI_Swwan", or:

cd ComfyUI/custom_nodes
git clone https://github.com/aining2022/ComfyUI_Swwan
cd ComfyUI_Swwan
pip install -r requirements.txt

Restart, then find RGBA Save (Swwan) under Swwan/RGBA.

The traps

The big one: don't skip the Post step. The most common "why is my saved PNG dark at the edges" post is someone feeding premultiplied RGB straight into a save. If your output looks like the subject got a permanent shadow around the outline, that's the double-alpha problem, and Post is the fix.

Second, this is PNG-only, and it will happily ignore that you wanted a JPEG. If you need format flexibility (or a flattened "no transparency" export for thumbnails or training sets), that's RGBA_Multi_Save's job, not this node's.

Third, remember the save happens against whatever alpha you give it. If you skipped RGBA_Safe_Pre entirely and loaded the raw inverted mask from Load Image as your alpha, you'll write a PNG where the subject is transparent and the background is solid. The mask from Load Image is 1 - alpha - this node trusts your alpha, it won't fix your wiring.