Access bitmap data directly to get pixel values instead of going through -[NSBitmapImageRep getPixel:atX:y], which is slowed by caching and locking overhead.
Access bitmap data directly to get pixel values instead of going through -[NSBitmapImageRep getPixel:atX:y], which is slowed by caching and locking overhead.

JackieXie168/skim,JackieXie168/skim,JackieXie168/skim,JackieXie168/skim,JackieXie168/skim