Question

Objective-C / Cocoa:
I need to load the image from a JPG file into a two dimensional array so that I can access each pixel. I am trying (unsuccessfully) to load the image into a NSBitmapImageRep. I have tried several variations on the following two lines of code:

NSString *filePath = [NSString stringWithFormat: @"%@%@",@"/Users/adam/Documents/phoneimages/", [outLabel stringValue]];  //this coming from a window control
NSImageRep *controlBitmap = [[NSImageRep alloc] imageRepWithContentsOfFile:filePath];

With the code shown, I get a runtime error: -[NSImageRep imageRepWithContentsOfFile:]: unrecognized selector sent to instance 0x100147070.

I have tried replacing the second line of code with:

NSImage *controlImage = [[NSImage alloc] initWithContentsOfFile:filePath];
NSBitmapImageRep *controlBitmap = [[NSBitmapImageRep alloc] initWithData:controlImage];

But this yields a compiler error ‘incompatible type’ saying that initWithData wants a NSData variable not an NSImage.

I have also tried various other ways to get this done, but all are unsuccessful either due to compiler or runtime error. Can someone help me with this? I will eventually need to load some PNG files in the same way (so it would be nice to have a consistent technique for both).

And if you know of an easier / simpler way to accomplish what I am trying to do (i.e., get the images into a two-dimensional array), rather than using NSBitmapImageRep, then please let me know! And by the way, I know the path is valid (confirmed with fileExistsAtPath) — and the filename in outLabel is a file with .jpg extension.

Thanks for any help!

Answer 1

Easy!

NSImage *controlImage = [[NSImage alloc] initWithContentsOfFile:filePath];
NSBitmapImageRep *imageRep = [[controlImage representations] objectAtIndex:0];

Then to get the actual bitmap pixel data:

unsigned char *pixelData = [imageRep bitmapData];

If your image has multiple representations (it probably doesn’t), you can get them out of that same array. The same code will work for your .png images.