Update README explanation

Author: Splendide-Imaginarius

README.md

@@ -2,6 +2,14 @@
 
 Do you have two images, one of which is a zoomed-in version of the other? Would you like to stitch the zoomed-in image into the zoomed-out image, to boost the resolution of that portion? Subimage Stitcher is designed to do this.
 
+## Comparison to Other Projects
+
+Most other image stitching tools are designed for panoramas, where each input image has a small overlap with its adjacent input images, and each input image has similar scale. They produce an output image whose dimensions and viewpoint are zoomed-out relative to the input images.
+
+Subimage Stitcher is different. It's designed for cases where the input images have large (maybe 100%) overlap, and very different scale. It produces an output image whose dimensions and viewpoint are identical to the outer input image, but with enhanced detail in the portion that corresponds to the inner input image.
+
+Use the right tool for the job!
+
 ## Installation
 
 * Install ImageMagick if you don't have it already.
@@ -17,7 +25,14 @@ subimage-stitcher --foreground "inputs/foreground.png" --background "inputs/back
 * The arguments to `--foreground` and `--background` are used for computing the transformation matrix.
 * The arguments to `--replace-foreground` and `--replace-background`, if present, are used in composing the output image. If they are not specified, the `--foreground` and `--background` images are used.
 * The output image has the dimensions of the `--background` argument, multiplied by the `--scale` argument.
-* If you're seeing bad matrix results, the `--feature-type`, `--subset-frac`, and `--no-cross-check` arguments are the most likely to help.
+* Three output composite images are produced: one with OpenCV interpolation, one with ImageMagick interpolation, and one with ImageMagick interpolation combined with a smooth blending of the foreground and the background.
+* An output warped image is produced; this is the foreground image in the same pose as the composite image, but without the background.
+* A keypoints map image is produced for debug purposes; this can be helpful for visualizing how well the feature detection/matching is working.
+* An output background image is produced; this is the same as the composite image but without the foreground. (It's identical to the input background image, just potentially at a different scale.)
+* An output stacked image is produced, if you want to look at the warped foreground and background images side-by-side.
+* If you're seeing bad warping results, the `--feature-type`, `--subset-frac`, and `--no-cross-check` arguments are the most likely to help.
+* The ImageMagick composite images are likely to look better to humans, but the OpenCV composite image is likely to work better as input to a subsequent Subimage Stitcher feature-detection pass. You can use the `--replace-foreground` or `--replace-background` arguments to get the best of both worlds.
+* Running the input images through Real-ESRGAN first seems to improve the reliabilty of Subimage Stitcher's feature detection.
 
 Run `subimage-stitcher --help` to see full command-line options.