UIImage与位图(RGBA8 Bitmaps)的相互转化

来自 http://paulsolt.com/2010/09/ios-converting-uiimage-to-rgba8-bitmaps-and-back/

下载：https://github.com/PaulSolt/UIImage-Conversion

ImageHelper.h

/*
 * The MIT License
 *
 * Copyright (c) 2011 Paul Solt, PaulSolt@gmail.com
 *
 * https://github.com/PaulSolt/UIImage-Conversion/blob/master/MITLicense.txt
 *
 */

#import <Foundation/Foundation.h>


@interface ImageHelper : NSObject {

}

/** Converts a UIImage to RGBA8 bitmap.
 @param image - a UIImage to be converted
 @return a RGBA8 bitmap, or NULL if any memory allocation issues. Cleanup memory with free() when done.
 */
+ (unsigned char *) convertUIImageToBitmapRGBA8:(UIImage *)image;

/** A helper routine used to convert a RGBA8 to UIImage
 @return a new context that is owned by the caller
 */
+ (CGContextRef) newBitmapRGBA8ContextFromImage:(CGImageRef)image;


/** Converts a RGBA8 bitmap to a UIImage. 
 @param buffer - the RGBA8 unsigned char * bitmap
 @param width - the number of pixels wide
 @param height - the number of pixels tall
 @return a UIImage that is autoreleased or nil if memory allocation issues
 */
+ (UIImage *) convertBitmapRGBA8ToUIImage:(unsigned char *)buffer 
	withWidth:(int)width
	withHeight:(int)height;

@end

ImageHelper.m
/*
 * The MIT License
 *
 * Copyright (c) 2011 Paul Solt, PaulSolt@gmail.com
 *
 * https://github.com/PaulSolt/UIImage-Conversion/blob/master/MITLicense.txt
 *
 */

#import "ImageHelper.h"


@implementation ImageHelper


+ (unsigned char *) convertUIImageToBitmapRGBA8:(UIImage *) image {

	CGImageRef imageRef = image.CGImage;

	// Create a bitmap context to draw the uiimage into
	CGContextRef context = [self newBitmapRGBA8ContextFromImage:imageRef];

	if(!context) {
		return NULL;
	}

	size_t width = CGImageGetWidth(imageRef);
	size_t height = CGImageGetHeight(imageRef);

	CGRect rect = CGRectMake(0, 0, width, height);

	// Draw image into the context to get the raw image data
	CGContextDrawImage(context, rect, imageRef);

	// Get a pointer to the data	
	unsigned char *bitmapData = (unsigned char *)CGBitmapContextGetData(context);

	// Copy the data and release the memory (return memory allocated with new)
	size_t bytesPerRow = CGBitmapContextGetBytesPerRow(context);
	size_t bufferLength = bytesPerRow * height;

	unsigned char *newBitmap = NULL;

	if(bitmapData) {
		newBitmap = (unsigned char *)malloc(sizeof(unsigned char) * bytesPerRow * height);

		if(newBitmap) {	// Copy the data
			for(int i = 0; i < bufferLength; ++i) {
				newBitmap[i] = bitmapData[i];
			}
		}

		free(bitmapData);

	} else {
		NSLog(@"Error getting bitmap pixel data\n");
	}

	CGContextRelease(context);

	return newBitmap;	
}

+ (CGContextRef) newBitmapRGBA8ContextFromImage:(CGImageRef) image {
	CGContextRef context = NULL;
	CGColorSpaceRef colorSpace;
	uint32_t *bitmapData;

	size_t bitsPerPixel = 32;
	size_t bitsPerComponent = 8;
	size_t bytesPerPixel = bitsPerPixel / bitsPerComponent;

	size_t width = CGImageGetWidth(image);
	size_t height = CGImageGetHeight(image);

	size_t bytesPerRow = width * bytesPerPixel;
	size_t bufferLength = bytesPerRow * height;

	colorSpace = CGColorSpaceCreateDeviceRGB();

	if(!colorSpace) {
		NSLog(@"Error allocating color space RGB\n");
		return NULL;
	}

	// Allocate memory for image data
	bitmapData = (uint32_t *)malloc(bufferLength);

	if(!bitmapData) {
		NSLog(@"Error allocating memory for bitmap\n");
		CGColorSpaceRelease(colorSpace);
		return NULL;
	}

	//Create bitmap context

	context = CGBitmapContextCreate(bitmapData, 
			width, 
			height, 
			bitsPerComponent, 
			bytesPerRow, 
			colorSpace, 
			kCGImageAlphaPremultipliedLast);	// RGBA
	if(!context) {
		free(bitmapData);
		NSLog(@"Bitmap context not created");
	}

	CGColorSpaceRelease(colorSpace);

	return context;	
}

+ (UIImage *) convertBitmapRGBA8ToUIImage:(unsigned char *) buffer 
		withWidth:(int) width
	   withHeight:(int) height {


	size_t bufferLength = width * height * 4;
	CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer, bufferLength, NULL);
	size_t bitsPerComponent = 8;
	size_t bitsPerPixel = 32;
	size_t bytesPerRow = 4 * width;

	CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
	if(colorSpaceRef == NULL) {
		NSLog(@"Error allocating color space");
		CGDataProviderRelease(provider);
		return nil;
	}

	CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault; 
	CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;

	CGImageRef iref = CGImageCreate(width, 
				height, 
				bitsPerComponent, 
				bitsPerPixel, 
				bytesPerRow, 
				colorSpaceRef, 
				bitmapInfo, 
				provider,	// data provider
				NULL,		// decode
				YES,			// should interpolate
				renderingIntent);

	uint32_t* pixels = (uint32_t*)malloc(bufferLength);

	if(pixels == NULL) {
		NSLog(@"Error: Memory not allocated for bitmap");
		CGDataProviderRelease(provider);
		CGColorSpaceRelease(colorSpaceRef);
		CGImageRelease(iref);		
		return nil;
	}

	CGContextRef context = CGBitmapContextCreate(pixels, 
				 width, 
				 height, 
				 bitsPerComponent, 
				 bytesPerRow, 
				 colorSpaceRef, 
				 kCGImageAlphaPremultipliedLast); 

	if(context == NULL) {
		NSLog(@"Error context not created");
		free(pixels);
	}

	UIImage *image = nil;
	if(context) {

		CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, width, height), iref);

		CGImageRef imageRef = CGBitmapContextCreateImage(context);

		// Support both iPad 3.2 and iPhone 4 Retina displays with the correct scale
		if([UIImage respondsToSelector:@selector(imageWithCGImage:scale:orientation:)]) {
			float scale = [[UIScreen mainScreen] scale];
			image = [UIImage imageWithCGImage:imageRef scale:scale orientation:UIImageOrientationUp];
		} else {
			image = [UIImage imageWithCGImage:imageRef];
		}

		CGImageRelease(imageRef);	
		CGContextRelease(context);	
	}

	CGColorSpaceRelease(colorSpaceRef);
	CGImageRelease(iref);
	CGDataProviderRelease(provider);

	if(pixels) {
		free(pixels);
	}	
	return image;
}

@end

这样使用
NSString *path = (NSString*)[[NSBundle mainBundle] pathForResource:@"Icon4" ofType:@"png"];
UIImage *image = [UIImage imageWithContentsOfFile:path];
int width = image.size.width;
int height = image.size.height;
 
    // Create a bitmap
unsigned char *bitmap = [ImageHelper convertUIImageToBitmapRGBA8:image];
 
    // Create a UIImage using the bitmap
UIImage *imageCopy = [ImageHelper convertBitmapRGBA8ToUIImage:bitmap withWidth:width withHeight:height];
 
    // Display the image copy on the GUI
UIImageView *imageView = [[UIImageView alloc] initWithImage:imageCopy];
 
    // Cleanup
free(bitmap);