How ComfyUI workflow data is stored in PNG images

PNG is a chain of chunks

After the eight-byte signature, a PNG is length + type + data + CRC, repeated until IEND. IHDR holds width and height. IDAT holds compressed pixels. Ancillary chunks can hold text without touching pixels.

tEXt is a keyword, a null byte, then a payload. ComfyUI commonly uses the keywords prompt and workflow. prompt is the API-style node graph. workflow is the UI graph with positions and links.

What we tested

The PNG chunk inspector was unit-tested against a synthetic PNG with an IHDR, a tEXt chunk, and IEND. The keyword and payload round-tripped. CRC failures are reported rather than ignored.

Interpreted fields such as sampler names from widget arrays are guesses. The raw JSON is the source of truth. ConvertPass labels missing fields as unknown.

If the chunks are missing

Saving through an editor, uploading to a social network, or converting via canvas will often drop tEXt. That does not prove the image was not generated. See the guide on missing prompt data.