I would like to write an app for Evernote that uses the annotation feature available for images.
As an example, the file below was annotated in Evernote and saved to disk.
If you open this image in Evernote or Skitch, you can modify the annotation, as if it was a vector file format (like SVG).
But the magic is that you can also open the same image file in any(!) image viewer as a normal PNG and you can still see the annotated image (magic !) but and you cannot edit the annotation.
So the secret behind the magic - in my understanding - is that this is saved in Special PNG format (Skitch PNG format) which contains:
1) the original, un-annotated image
2) annotation information (text content, position, size, font color, etc..)
3) the flattened annotated PNG image (which is what gets displayed when you open this file in a "normal" image viewer).
Now the questions:
How can I extract the annotation information from this Special PNG format ?
How is the annotation information stored in this image?
Is this described somewhere in detail ?
I have searched the web very throughly and did not find this information anywhere. I wonder - is this information some kind of secret or am I just the first one who wants to know how this works and use it to develop Evernote compatible software ?
Is it possible to get this information from Evernote so that I can develop an application that is compatible with Evernote's format and users of my application can benefit from exchanging information between my application and their Evernote accounts ?