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iOS中的圖像處理（一）——基礎濾鏡
最近在稍微做一些整理，翻起這部分的代碼，發現是兩個多月前的了。
這裏討論的是基於RGBA模型下的圖像處理，即將變換作用在每個像素上。
代碼是以UIImage的category形式存在的：
typedef struct _singleRGBA
{
unsigned char red;
unsigned char green;
unsigned char blue;
unsigned char alpha;
} RGBA;
@interface UIImage (ImageFilter)
- (UIImage*)applyFilter:(FilterFunction)filter context:(void*)context
{
CGImageRef inImage = self.CGImage;
CFDataRef m_DataRef = CGDataProviderCopyData(CGImageGetDataProvider(inImage));
UInt8 *m_PixelBuf = (UInt8 *)CFDataGetBytePtr(m_DataRef);
int length = CFDataGetLength(m_DataRef);
for (int i=0; i<length; i+=4) {
filter(m_PixelBuf, i, context);
}
CGContextRef ctx = CGBitmapContextCreate(m_PixelBuf,
CGImageGetWidth(inImage),
CGImageGetHeight(inImage),
CGImageGetBitsPerComponent(inImage),
CGImageGetBytesPerRow(inImage),
CGImageGetColorSpace(inImage),
CGImageGetBitmapInfo(inImage)
);
CGImageRef imageRef = CGBitmapContextCreateImage(ctx);
CGContextRelease(ctx);
UIImage *finalImage = [UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);
CFRelease(m_DataRef);
return finalImage;
}
typedef void (*FilterFunction)(UInt8 *pixelBuf, UInt32 offset, void *context);
在此基礎上，我們可以把每個變換操作獨立出來，比如調整亮度、對比度、色調、透明度等：
void filterOpacity(UInt8 *pixelBuf, UInt32 offset, void *context)
{
double val = *((double*)context);
int a = offset+3;
int alpha = pixelBuf[a];
pixelBuf[a] = SAFECOLOR(alpha * val);
}
void filterBrightness(UInt8 *pixelBuf, UInt32 offset, void *context)
{
double t = *((double*)context);
int r = offset;
int g = offset+1;
int b = offset+2;
int red = pixelBuf[r];
int green = pixelBuf[g];
int blue = pixelBuf[b];
pixelBuf[r] = SAFECOLOR(red * t);
pixelBuf[g] = SAFECOLOR(green * t);
pixelBuf[b] = SAFECOLOR(blue * t);
}
void filterSaturation(UInt8 *pixelBuf, UInt32 offset, void *context)
{
double t = *((double*)context); // t (- [0, 2]
int r = offset;
int g = offset+1;
int b = offset+2;
int red = pixelBuf[r];
int green = pixelBuf[g];
int blue = pixelBuf[b];
red = red * (0.3086 * (1-t) + t) + green * (0.6094 * (1-t)) + blue * (0.0820 * (1-t));
green = red * (0.3086 * (1-t)) + green * ((0.6094 * (1-t)) + t) + blue * (0.0820 * (1-t));
blue = red * (0.3086 * (1-t)) + green * (0.6094 * (1-t)) + blue * ((0.0820 * (1-t)) + t);
pixelBuf[r] = SAFECOLOR(red);
pixelBuf[g] = SAFECOLOR(green);
pixelBuf[b] = SAFECOLOR(blue);
}
void filterContrast(UInt8 *pixelBuf, UInt32 offset, void *context)
{
double t = *((double*)context); // t (- [0, 10]
int r = offset;
int g = offset+1;
int b = offset+2;
int red = pixelBuf[r];
int green = pixelBuf[g];
int blue = pixelBuf[b];
red = red * t + 128 * (1-t);
green = green * t + 128 * (1-t);
blue = blue * t + 128 * (1-t);
pixelBuf[r] = SAFECOLOR(red);
pixelBuf[g] = SAFECOLOR(green);
pixelBuf[b] = SAFECOLOR(blue);
}
void filterPosterize(UInt8 *pixelBuf, UInt32 offset, void *context)
{
double levels = *((double*)context);
if (levels == 0) levels = 1; // avoid divide by zero
int step = 255 / levels;
int r = offset;
int g = offset+1;
int b = offset+2;
int red = pixelBuf[r];
int green = pixelBuf[g];
int blue = pixelBuf[b];
pixelBuf[r] = SAFECOLOR((red / step) * step);
pixelBuf[g] = SAFECOLOR((green / step) * step);
pixelBuf[b] = SAFECOLOR((blue / step) * step);
}
void filterDesaturate(UInt8 *pixelBuf, UInt32 offset, void *context)
{
int r = offset;
int g = offset+1;
int b = offset+2;
int red = pixelBuf[r];
int green = pixelBuf[g];
int blue = pixelBuf[b];
red = red * 0.3086 + green * 0.6094 + blue * 0.0820;
green = red * 0.3086 + green * 0.6094 + blue * 0.0820;
blue = red * 0.3086 + green * 0.6094 + blue * 0.0820;
pixelBuf[r] = SAFECOLOR(red);
pixelBuf[g] = SAFECOLOR(green);
pixelBuf[b] = SAFECOLOR(blue);
}
void filterInvert(UInt8 *pixelBuf, UInt32 offset, void *context)
{
int r = offset;
int g = offset+1;
int b = offset+2;
int red = pixelBuf[r];
int green = pixelBuf[g];
int blue = pixelBuf[b];
pixelBuf[r] = SAFECOLOR(255-red);
pixelBuf[g] = SAFECOLOR(255-green);
pixelBuf[b] = SAFECOLOR(255-blue);
}
void filterTint(UInt8 *pixelBuf, UInt32 offset, void *context)
{
RGBA *rgbaArray = (RGBA*)context;
RGBA maxRGBA = rgbaArray[0];
RGBA minRGBA = rgbaArray[1];
int r = offset;
int g = offset+1;
int b = offset+2;
int red = pixelBuf[r];
int green = pixelBuf[g];
int blue = pixelBuf[b];
pixelBuf[r] = SAFECOLOR((red - minRGBA.red) * (255.0 / (maxRGBA.red - minRGBA.red)));
pixelBuf[g] = SAFECOLOR((green - minRGBA.green) * (255.0 / (maxRGBA.green - minRGBA.green)));
pixelBuf[b] = SAFECOLOR((blue - minRGBA.blue) * (255.0 / (maxRGBA.blue - minRGBA.blue)));
}
其中SAFECOLOR宏如下：
#define SAFECOLOR(color) MIN(255,MAX(0,color))
最後，拿一張帥氣的Andy照片來實踐下，希望沒有侵犯到肖像權。
原圖如下：
通過以下四種變換，可以分別得到四張處理過的圖片：
return [originImage changeOpacityByFactor:0.5];
return [originImage changeBrightnessByFactor:1.2];
return [originImage changeSaturationByFactor:2.0];
return [originImage tintWithMaxRGBA:(RGBA){190, 190, 230} minRGBA:(RGBA){50, 35, 10}];
最後更新：2017-04-02 16:48:12