iphone - 如何从 CGImage 获取原始像素数据

Question

如何在缩放和移动后获取 UIImage 的像素数据，我想获取 CGImage 像素数据，然后从 CGImage 像素数据中获取 UIImage。我们该怎么做呢？

Answer 1

您可以通过调用获取原始数据

CFDataRef rawData = CGDataProviderCopyData(CGImageGetDataProvider(aCGImageRef));

您可以像这样逐步遍历像素：

UInt8 * buf = (UInt8 *) CFDataGetBytePtr(rawData); 
CFIndex length = CFDataGetLength(rawData);

for(unsigned long i=0; i<length; i+=4)
{
    int r = buf[i];
    int g = buf[i+1];
    int b = buf[i+2];
     }
CFRelease(rawData);

Answer 2

尝试这个。这将为您提供图像选定像素的偏移、Alpha、RGB 颜色等。

源代码：-

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event 
{
UITouch *touch = [[event allTouches] anyObject]; 

CGPoint startLocation   = [touch locationInView:self.view];

    if ([touch view] == YourImageView)
    {
        CGPoint location = [touch YourImageView];
        [self getPixelColorAtLocation:location];
        if((alpha==255)||(alpha==0))
        {
            //perform Your task
        }
    }
} 


- (UIColor*) getPixelColorAtLocation:(CGPoint)point 
{

UIColor* color = nil;

CGImageRef inImage;

inImage = YourImageView.image.CGImage;


// Create off screen bitmap context to draw the image into. Format ARGB is 4 bytes for each pixel: Alpa, Red, Green, Blue
CGContextRef cgctx = [self createARGBBitmapContextFromImage:inImage];
if (cgctx == NULL) { return nil; /* error */ }

size_t w = CGImageGetWidth(inImage);
size_t h = CGImageGetHeight(inImage);
CGRect rect = {{0,0},{w,h}};


// Draw the image to the bitmap context. Once we draw, the memory 
// allocated for the context for rendering will then contain the 
// raw image data in the specified color space.
CGContextDrawImage(cgctx, rect, inImage); 

// Now we can get a pointer to the image data associated with the bitmap
// context.
unsigned char* data = CGBitmapContextGetData (cgctx);
if (data != NULL) {
    //offset locates the pixel in the data from x,y. 
    //4 for 4 bytes of data per pixel, w is width of one row of data.
    int offset = 4*((w*round(point.y))+round(point.x));
    alpha =  data[offset]; 
    int red = data[offset+1]; 
    int green = data[offset+2]; 
    int blue = data[offset+3]; 
    NSLog(@"offset: %i colors: RGB A %i %i %i  %i",offset,red,green,blue,alpha);
    color = [UIColor colorWithRed:(red/255.0f) green:(green/255.0f) blue:(blue/255.0f) alpha:(alpha/255.0f)];
}

// When finished, release the context
//CGContextRelease(cgctx); 
// Free image data memory for the context
if (data) { free(data); }

return color;
}

- (CGContextRef) createARGBBitmapContextFromImage:(CGImageRef)inImage 
{
CGContextRef    context = NULL;
CGColorSpaceRef colorSpace;
void *          bitmapData;
int             bitmapByteCount;
int             bitmapBytesPerRow;

// Get image width, height. We'll use the entire image.
size_t pixelsWide = CGImageGetWidth(inImage);
size_t pixelsHigh = CGImageGetHeight(inImage);

// Declare the number of bytes per row. Each pixel in the bitmap in this
// example is represented by 4 bytes; 8 bits each of red, green, blue, and
// alpha.
bitmapBytesPerRow   = (pixelsWide * 4);
bitmapByteCount     = (bitmapBytesPerRow * pixelsHigh);

// Use the generic RGB color space.
colorSpace = CGColorSpaceCreateDeviceRGB();

if (colorSpace == NULL)
{
    fprintf(stderr, "Error allocating color space\n");
    return NULL;
}

// Allocate memory for image data. This is the destination in memory
// where any drawing to the bitmap context will be rendered.
bitmapData = malloc( bitmapByteCount );
if (bitmapData == NULL) 
{
    fprintf (stderr, "Memory not allocated!");
    CGColorSpaceRelease( colorSpace );
    return NULL;
}

// Create the bitmap context. We want pre-multiplied ARGB, 8-bits 
// per component. Regardless of what the source image format is 
// (CMYK, Grayscale, and so on) it will be converted over to the format
// specified here by CGBitmapContextCreate.
context = CGBitmapContextCreate (bitmapData,
                                 pixelsWide,
                                 pixelsHigh,
                                 8,      // bits per component
                                 bitmapBytesPerRow,
                                 colorSpace,
                                 kCGImageAlphaPremultipliedFirst);
if (context == NULL)
{
    free (bitmapData);
    fprintf (stderr, "Context not created!");
}

// Make sure and release colorspace before returning
CGColorSpaceRelease( colorSpace );

return context;
}

希望能帮助到你。谢谢 ：）