The document discusses the effect of varying the number of samples on image quality through upsampling and downsampling. It shows how downsampling an image by omitting pixel values reduces the image resolution and quality. In contrast, upsampling does not remove pixel values but instead interpolates new values, so downsampling the upsampled image back to the original size nearly recovers the original quality. The key factors are that downsampling removes information while upsampling preserves information through interpolation.