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In objective c,

I need to convert a UIImage into something that matches the following type:

const unsigned char myImg[6300] = { 0xff,0xff,0xff,0xff,0xff,0xff,0x0,0x0,0x0,
0x0,0xff,0xff,0x0,0x0,0xff,0xff,0xff,0xff,0x0,0x0,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0x0,0x0,0xff,0xff, etc etc etc }

I've read the NSData docs, and tried:

self.animalImage = [UIImage imageNamed:@"animal.png"];
self.animalData = UIImagePNGRepresentation(self.animalImage);
NSUInteger size = [self.animalData length] / sizeof(unsigned char);
unsigned char* array = (unsigned char*) [self.animalData bytes];

But the result is garbage or nil, I need it to match the above format exactly. Any thoughts? Thanks in advance for any tips!

Alfie Hanssen
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  • Do you really want PNG data? Or are you looking for a bitmap representation of your image? – Carl Norum Jan 12 '12 at 22:36
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    What exactly is your formatting example supposed to be? Do you want some kind of binary image where every pixel is either 0 or 255, or do you want the standard RGB bitmap representation where each triple of bytes is the red, green, and blue value of a pixel? Right now what you are getting are the bytes that represent a PNG (i.e. compressed) version of the image. – UIAdam Jan 12 '12 at 22:40

1 Answers1

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You say your result is "garbage or nil" but the documentation says it will either return the byte data of the image or nil if it encounters an error.

https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIKitFunctionReference/#//apple_ref/c/func/UIImagePNGRepresentation

I don't see how it could generate different results with the same image, so I'm going to guess you tried it with some different images, perhaps some of them not actually PNG images. The ones that it could not parse properly returned nil and the "garbage" you describe is probably actually the data you want.

Once you have your NSData* instance you can use enumerateByteRangesUsingBlock to build your new array that you need.

https://developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Classes/NSData_Class/

slf
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