Readme written

libpme.py

@@ -1,14 +1,14 @@
 #!/usr/bin/env python3
 # PNG Metadata Editor
 # Niles Rogoff 2016
-import struct, zlib, copy
+import zlib, copy
+class color_types(object):
+    GREYSCALE = 0
+    RGB = 2
+    PALETTE = 3
+    GREYSCALE_WITH_ALPHA = 4
+    RGB_WITH_ALPHA = 6
 class PME(object):
-	class color_types(object):
-		GREYSCALE = 0
-		RGB = 2
-		PALETTE = 3
-		GREYSCALE_WITH_ALPHA = 4
-		RGB_WITH_ALPHA = 6
 	def _int(self, binary):
 		return int.from_bytes(binary, byteorder="big")
 	def _bytes(self, integer, length):
@@ -40,7 +40,7 @@ class PME(object):
 			]
 			self.width = self.height = 0 # the user can decide
 			self.bit_depth = 8 # a sane default
-			self.color_type = self.color_types.RGB_WITH_ALPHA
+			self.color_type = color_types.RGB_WITH_ALPHA
 			self.compression_method = 0
 			self.filter_method = 0 # The only one as far as I know
 			self.interlace_method = 0

readme.md

@@ -0,0 +1,81 @@
+# PNG Metadata Editor
+
+This library was written for a competition between me and Ethan, who was going to write this same thing in Java. He failed.
+
+You can initialize a PME instance by passing it a filename to an already existing file, or no arguments, like this:
+
+    img = new libpme.PME("test.png");
+	# or
+    img = new libpme.PME();
+
+If the file is not valid, it will throw an exception
+
+## Properties
+
+These are the values that you can access or change. Most are self explanatory. Changing any of these will automatically call `recalculate_IHDR`. If you really want to suppress this behavior, just back up the IHDR chunk before changing the value. The defaults for an object created with no filename are displayed in parenthesis
+
+	width (0)
+	height (0)
+	bit_depth (8)
+	color_type (color_types.RGB_WITH_ALPHA (6))
+	compression_method (0)
+	filter_method (0)
+	interlace_method (0)
+
+## Methods
+Here are the methods you can call on an image, in no particular order
+
+### `recalculate_properties`
+This simply recalculates the seven properties listed above from the data currently in the IHDR chunk. 
+
+	img.height = 400
+	img.chunks[0][2] = b'\x00\x00\x00\x00\x00\x00\x00\x00\x08\x06\x00\x00\x00'
+	# img.height remains unchanged at 400
+	img.recalculate_properties()
+	# img.height is now set to 0
+
+### `recalculate_IHDR`
+This takes the seven properties listed above and destructively replaces the first chunk's data and crc with updated fields
+
+	img.width = 0
+	# img.chunks[0][2] is now set to b'\x00\x00\x00\x00\x00\x00\x00\x00\x08\x06\x00\x00\x00'
+	img.width = 400
+	img.recalculate_IHDR()
+	# img.chunks[0][2] is now set to b'\x00\x00\x01\x90\x00\x00\x00\x00\x08\x06\x00\x00\x00'
+
+### `recalculate_crc`
+This takes an index of a chunk (see below) and overwrites the crc in that chunk with a newly calculated crc based on that chunk's label and data
+
+	img.color_type = libpme.color_types.RGB
+	img.width = img.height = 1
+	img.chunks[1][2] = b'\x00\xFF\x00\x00' # a 1x1 red image, assuming that the second chunk is the only IDAT chunk
+	img.recalculate_crc(1) # img.chunks[1][3] is now set to b'T\xbb\xd3\xea'
+
+### `recalculate_length`
+This takes an index of a chunk (see below) and updates the length of that chunk with a newly calculated length based on that chunk's data
+
+	img.color_type = libpme.color_types.RGB
+	img.width = img.height = 1
+	img.chunks[1][2] = img.compress(b'\x00\xFF\x00\x00') # a 1x1 red image, assuming that the second chunk is the only IDAT chunk
+	img.recalculate_length(1) # img.chunks[1][0] is now set to b'\x00\x00\x00\x04'
+
+### `save`
+This saves the image to the disk, overwriting a file if it was already there. If the object was created from an existing file and no arguments are passed, it will use the original file. 
+
+	img.save("red1.png")
+	img.save() # Only if the object was created from an existing file.
+
+### `get_concatenated_idat_data`
+Concatenates the (still compressed) data of each IDAT chunk, then returns it.
+
+	img.width = 2
+	img.chunks.insert(2, [b'\x00\x00\x00\x03', b'IDAT', img.compress(b'\x00\xFF\x00'), b'j\xee\xb3\xd0']) # making it a 2x1 image with a red and a green pixel
+	img.decompress(img.get_concatenated_idat_data()) # returns '\x00\xFF\x00\x00\x00\xFF\x00';
+
+### `write_raw_idat_data`
+Deletes all IDAT chunks except the first one, then sets that chunk's data to the argument it was passed, and recalculates its crc and length.
+
+	img.write_raw_idat_data(img.compress(b'\x00\x00\x00\xFF\x00\x00\xFF')) # a 2x1 image with all blue pixels
+
+## Indexes
+Any function that takes an index can be passed either the numerical index of the chunk (so 0 for IDAT, 1 for the second chunk, -1 for the last chunk, etc..), or a list that exists in `img.chunks`, or a 4-length bytes object that is equal to the label of one of the chunks in the image. If a chunk with that label appears more than once, the first one will be used