Overview
Ultimate SD Upscale is installed as a custom node through Manager and requires a ComfyUI restart. For the upscaling stage, it replaces the ordinary KSampler.
The node receives:
Model from the checkpoint.
Positive conditioning.
Negative conditioning.
VAE from the checkpoint.
A loaded input image.
An upscale model such as 4x-UltraSharp.
If a 512 by 512 image is enlarged by two, the process uses a two-by-two grid of four sections. Each section is processed with image-to-image. The four regenerated sections are then stitched into one 1024 by 1024 image.
The critical control is denoise. A low value, such as 0.2 or even 0.15, retains most of the original tile while allowing the model to generate finer detail. This is why the result can be sharper than a direct upscaler without becoming a completely new image.
Tile width and tile height define the dimensions used for each tile. The starting recommendation is to match them to the dimensions of the original input. For a 512 by 512 source, the tile width and height are set to 512.
Mask blur and tile padding affect how the processed tiles blend when they are reassembled. The default values are retained unless visible lines appear between tiles. In that failure case, those settings can be adjusted to improve the seams.
A fourfold enlargement can be produced in one 4x pass or by chaining two 2x Ultimate SD Upscale nodes. The first converts 512 by 512 to 1024 by 1024. The second receives that result and enlarges it again. Because its input is now 1024 by 1024, its tile width and height are updated to 1024.
Ctrl+Shift+V is useful here: duplicating the first Ultimate SD Upscale node with preserved connections automatically reconnects the shared model, prompts, VAE, and upscaler model. The original image connection is then removed and replaced with the output of the first 2x stage.