OpenCV CV_8SC_0

OpenCV CV_8SC_0 computes the OpenCV type constant for a signed 8-bit image with a given channel count. CV_8SC(1) returns 1; CV_8SC(3) returns 17. It's the sibling of the far more famous CV_8UC (unsigned 8-bit) - the S vs U is signed vs unsigned, and it matters more than most people realize.

This node is part of geroldmeisinger/opencv-comfyui, the auto-generated pack that wraps every top-level cv2 function as a ComfyUI node. About 635 functions, most of them plain wrappers, and the author tells you up front to expect dragons. CV_8SC_0 just calls cv2.CV_8SC(channels) and returns the packed constant.

Why signed 8-bit is a thing

Almost every image you touch in ComfyUI is unsigned 8-bit: CV_8U is depth 0, so CV_8UC(3) = 16 and that's your normal BGR color frame. Signed 8-bit (CV_8S, depth 1) holds values from −128 to 127 instead of 0–255. It shows up when you're working with difference images, gradients, or error maps - data where a pixel genuinely wants to be negative. If you're doing edge detection or optical-flow-style work and a function in this pack demands a type constant, CV_8SC_0 is how you say "signed bytes, N channels" without memorizing the formula 1 + (channels - 1) * 8.

Honest take: for most ComfyUI workflows this node will sit in your sidebar unused. That's fine - it's a building block for when the pack's own cv2 functions start asking for type arguments you'd otherwise have to hardcode.

Inputs and outputs

• channels (INT) - how many channels you're encoding. 1 for single-channel signed data, 3 for signed color.
• int (INT, output) - the packed type code to feed downstream.

Install

Install through ComfyUI Manager (search opencv-comfyui) or by hand:

cd ComfyUI/custom_nodes
git clone https://github.com/geroldmeisinger/opencv-comfyui
pip install opencv-contrib-python

Restart ComfyUI. No model files to fetch.

The two things that actually bite people

First, package-name confusion: the README tells you to pip install opencv-python-contrib, which is wrong - the real PyPI package is opencv-contrib-python, and that's what the pack's requirements.txt pins. Use that one. If you later see Cannot import name 'guidedFilter' from 'cv2.ximgproc', you have conflicting OpenCV installs, which is a known ecosystem headache (the README links the LayerStyle issue that covers it).

Second, remember the pack's type discipline: ComfyUI IMAGE tensors are RGB float32 in 0–1, while OpenCV nparrays are BGR uint8 in 0–255. You convert with Image2Nparray/Nparrays2Image and use cvtColor for channel changes. A signed 8-bit image is one more step away from "a normal picture" - if a node downstream suddenly errors on an unexpected type, check that you didn't feed a signed buffer where the function wanted unsigned.