Why "Upscale Image Using Model" outputs distorted image
I have been learning comfyui and image generation in general on my own.
I wanted to upscale the image. "Upscale Image Using Model" expects an image, and when I pass an image, I get a distorted image (photo 1) as an output from the model upscale.
I could not figure out why, then I loaded some templates for upscale and I noticed that they are using "Upscale Image by" as a pipe before "Upscale Image Using Model". I added it, and it worked like a charm, outputs a normal upscale image (photo 2)
"Upscale Image by" with scale_by parameter set to 1.0 does nothing different to the size of an image. Also, some templates were using "Scale Image to Total Pixels" instead of "Upscale Image by", tried both; the image size stays the same, and "Upscale Image Using Model" outputs a normal upscale image.
I thought it might be a mask. "Load Image" output could be an RGBA instead of an RGB image. I used node "Image Remove Alpha" instead of "Upscale Image by" and the result was a distorted image. So it is not alpha.
My question is what else "Upscale Image by" and "Scale Image to Total Pixels" do to make "Upscale Image Using Model" work?