README: Add percetual encoding idea

Linking to ipfs-inactive/faq#15

README.md

@@ -194,6 +194,14 @@ Putting serialized IPLD structure into database/IPFS as JSON blob?
 [GEGL](http://gegl.org), the image processing library used by imgflo-server and GIMP
 * Consider extending for video
 
+## Ideas
+
+### Perceptual encoding
+Right now, we can deducplicate parts of images when the encoded representation of tiles are identical.
+However even the tiniest, impercievable change, like a 1 bit quantification error, will invalidate deduplication.
+Some [existing discussion here](https://github.com/ipfs/faq/issues/15), with references to academic papers.
+
+
 ## Contributors
 
 * [@Kubuxu](https://github.com/Kubuxu)

package.json

@@ -34,6 +34,7 @@
     "mocha": "^2.5.3"
   },
   "dependencies": {
+    "canvas": "^1.3.16",
     "ipfs-api": "^4.1.0",
     "ipfs-ipld": "^2.0.0",
     "ipld": "^0.6.0"

src/image.coffee

@@ -1,7 +1,10 @@
 
 ipfsIPLD = require 'ipfs-ipld'
 ipld = require 'ipld'
+Canvas = require 'canvas'
+Image = Canvas.Image
 
+# TODO: use a plain JS object or class, with have save/load to IPLD/MerkleDAG
 serializeImage = (shape, tilehashes) ->
   image =
     'ipld-image-version': 1
@@ -41,6 +44,22 @@ repeatedImage = (shape, tilehash) ->
       tiles.push tilehash
   return tiles
 
+# TODO: don't instead render into memory, find out how to concat PNG IDAT chunks
+# TODO: support cropping
+# TODO: support 
+renderBlob = (image) ->
+  imageSize =
+    x: image.tilesize.x*image.tiles.x
+    y: image.tilesize.y*image.tiles.y
+  console.log ''
+
+  canvas = new Canvas(200, 200)
+  img = new Image;
+  img.src = canvas.toBuffer();
+  ctx.drawImage(img, 0, 0, 50, 50);
+  ctx.drawImage(img, 50, 0, 50, 50);
+  ctx.drawImage(img, 100, 0, 50, 50);
+
 module.exports =
   repeat: repeatedImage
   construct: serializeImage