将图像转换为灰度
问题描述:
我想通过以下方式将图像转换为灰度:
I am trying to convert an image into grayscale in the following way:
#define bytesPerPixel 4
#define bitsPerComponent 8
-(unsigned char*) getBytesForImage: (UIImage*)pImage
{
CGImageRef image = [pImage CGImage];
NSUInteger width = CGImageGetWidth(image);
NSUInteger height = CGImageGetHeight(image);
NSUInteger bytesPerRow = bytesPerPixel * width;
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
unsigned char *rawData = malloc(height * width * 4);
CGContextRef context = CGBitmapContextCreate(rawData, width, height, bitsPerComponent, bytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colorSpace);
CGContextDrawImage(context, CGRectMake(0, 0, width, height), image);
CGContextRelease(context);
return rawData;
}
-(UIImage*) processImage: (UIImage*)pImage
{
DebugLog(@"processing image");
unsigned char *rawData = [self getBytesForImage: pImage];
NSUInteger width = pImage.size.width;
NSUInteger height = pImage.size.height;
DebugLog(@"width: %d", width);
DebugLog(@"height: %d", height);
NSUInteger bytesPerRow = bytesPerPixel * width;
for (int xCoordinate = 0; xCoordinate < width; xCoordinate++)
{
for (int yCoordinate = 0; yCoordinate < height; yCoordinate++)
{
int byteIndex = (bytesPerRow * yCoordinate) + xCoordinate * bytesPerPixel;
//Getting original colors
float red = ( rawData[byteIndex] / 255.f );
float green = ( rawData[byteIndex + 1] / 255.f );
float blue = ( rawData[byteIndex + 2] / 255.f );
//Processing pixel data
float averageColor = (red + green + blue) / 3.0f;
red = averageColor;
green = averageColor;
blue = averageColor;
//Assigning new color components
rawData[byteIndex] = (unsigned char) red * 255;
rawData[byteIndex + 1] = (unsigned char) green * 255;
rawData[byteIndex + 2] = (unsigned char) blue * 255;
}
}
NSData* newPixelData = [NSData dataWithBytes: rawData length: height * width * 4];
UIImage* newImage = [UIImage imageWithData: newPixelData];
free(rawData);
DebugLog(@"image processed");
return newImage;
}
所以当我想转换一个图像时,我只是调用processImage :
So when I want to convert an image I just call processImage:
imageToDisplay.image = [self processImage: image];
但不显示imageToDisplay。可能有什么问题?
But imageToDisplay doesn't display. What may be the problem?
谢谢。
答
发生在你使用这个功能?该函数是否返回无效图像,或者显示是否无法正确显示?
What exactly takes place when you use this function? Is the function returning an invalid image, or is the display not showing it correctly?
这是我用于转换为灰度的方法。
This is the method I use to convert to greyscale.
- (UIImage *) convertToGreyscale:(UIImage *)i {
int kRed = 1;
int kGreen = 2;
int kBlue = 4;
int colors = kGreen | kBlue | kRed;
int m_width = i.size.width;
int m_height = i.size.height;
uint32_t *rgbImage = (uint32_t *) malloc(m_width * m_height * sizeof(uint32_t));
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate(rgbImage, m_width, m_height, 8, m_width * 4, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipLast);
CGContextSetInterpolationQuality(context, kCGInterpolationHigh);
CGContextSetShouldAntialias(context, NO);
CGContextDrawImage(context, CGRectMake(0, 0, m_width, m_height), [i CGImage]);
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
// now convert to grayscale
uint8_t *m_imageData = (uint8_t *) malloc(m_width * m_height);
for(int y = 0; y < m_height; y++) {
for(int x = 0; x < m_width; x++) {
uint32_t rgbPixel=rgbImage[y*m_width+x];
uint32_t sum=0,count=0;
if (colors & kRed) {sum += (rgbPixel>>24)&255; count++;}
if (colors & kGreen) {sum += (rgbPixel>>16)&255; count++;}
if (colors & kBlue) {sum += (rgbPixel>>8)&255; count++;}
m_imageData[y*m_width+x]=sum/count;
}
}
free(rgbImage);
// convert from a gray scale image back into a UIImage
uint8_t *result = (uint8_t *) calloc(m_width * m_height *sizeof(uint32_t), 1);
// process the image back to rgb
for(int i = 0; i < m_height * m_width; i++) {
result[i*4]=0;
int val=m_imageData[i];
result[i*4+1]=val;
result[i*4+2]=val;
result[i*4+3]=val;
}
// create a UIImage
colorSpace = CGColorSpaceCreateDeviceRGB();
context = CGBitmapContextCreate(result, m_width, m_height, 8, m_width * sizeof(uint32_t), colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipLast);
CGImageRef image = CGBitmapContextCreateImage(context);
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
UIImage *resultUIImage = [UIImage imageWithCGImage:image];
CGImageRelease(image);
free(m_imageData);
// make sure the data will be released by giving it to an autoreleased NSData
[NSData dataWithBytesNoCopy:result length:m_width * m_height];
return resultUIImage;
}