In focus-blurred images, the blur spreads the information about certain pixels throughout a region of the image. (Objects appear larger and fainter because of t

In focus-blurred images, the blur spreads the information about certain pixels throughout a region of the image. (Objects appear larger and fainter because of this when they are blurred. It's why you can shoot through a mesh-wire fence with a wide lens aperture, for example, and not see the fence.) This 'spread out' information is being used to reconstruct an approximation of the original image. However, when images are downscaled, all the information from 'subpixels' is kept within the reduced-resolution-image-pixel, and all replaced with a single RGB value. There is no 'spread out' information from those pixels. The 'blur' only applies to a region with sharp edges that exactly coincide with the unit of information. So, none of the data from the sub-pixels remain. To reconstruct the pixels that were within you have to essentially guess based on the context of the surrounding pixels.