透明图绘制背景（证件照换底色）

致谢：感谢宝锋同学对方法一提供的思路；方法二则是完全是宝锋同学提供的代码。

方法一：

- (void)changeBgColorWithColorCode:(NSString *)colorCode {
    CGImageRef cgimage = [self.alphaImage CGImage];
    size_t width = CGImageGetWidth(cgimage); // 图片宽度
    size_t height = CGImageGetHeight(cgimage); // 图片高度
    unsigned char *data = calloc(width * height * 4, sizeof(unsigned char)); // 取图片首地址
    size_t bitsPerComponent = 8; // r g b a 每个component bits数目
    size_t bytesPerRow = width * 4; // 一张图片每行字节数目 (每个像素点包含r g b a 四个字节)
    CGColorSpaceRef space = CGColorSpaceCreateDeviceRGB(); // 创建rgb颜色空间
    CGContextRef context =
    CGBitmapContextCreate(data,
                          width,
                          height,
                          bitsPerComponent,
                          bytesPerRow,
                          space,
                          kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
    UIColor *fillColor;
    if ([colorCode isEqualToString:@"white"]) {
　　　　　//白色
        fillColor = [UIColor whiteColor];
        CGContextSetFillColorWithColor(context, fillColor.CGColor);
        CGContextFillRect(context, CGRectMake(0, 0, width, height));
        CGContextFillPath(context);
    } else if ([colorCode isEqualToString:@"blue"]) {
　　　　　//蓝色
        fillColor = [UIColor colorWithHex:0x3C90E8];
        CGContextSetFillColorWithColor(context, fillColor.CGColor);
        CGContextFillRect(context, CGRectMake(0, 0, width, height));
        CGContextFillPath(context);
    } else if ([colorCode isEqualToString:@"red"]) {
　　　　　//红色
        fillColor = [UIColor colorWithHex:0xF00001];
        CGContextSetFillColorWithColor(context, fillColor.CGColor);
        CGContextFillRect(context, CGRectMake(0, 0, width, height));
        CGContextFillPath(context);
    } else if ([colorCode isEqualToString:@"blue_gradual"]) {
　　　　 //蓝色渐变
        CGColorRef startColor = [UIColor colorWithRed:60/255.f green:144/255.f blue:232/255.f alpha:1].CGColor;
        CGColorRef endColor = [UIColor whiteColor].CGColor;
        NSArray *colors = @[(__bridge id)startColor,(__bridge id)endColor];
        CGFloat locations[] = { 0.0, 1.0 };
        CGGradientRef gradient = CGGradientCreateWithColors(space, (__bridge CFArrayRef) colors, locations);
//        CGFloat components[] = {
//            60/255.f,144/255.f,232/255.f,1,
//            1,1,1,1
//        };
//        CGGradientRef gradient = CGGradientCreateWithColorComponents(space, components, locations, 2);
        CGContextDrawLinearGradient(context, gradient, CGPointMake(width, height), CGPointMake(0, 0), 0);
    } else if ([colorCode isEqualToString:@"red_gradual"]) {
　　　　　//红色渐变
        CGColorRef startColor = [UIColor colorWithRed:240/255.f green:0/255.f blue:1/255.f alpha:1].CGColor;
        CGColorRef endColor = [UIColor whiteColor].CGColor;
        NSArray *colors = @[(__bridge id)startColor,(__bridge id)endColor];
        CGFloat locations[] = { 0.0, 1.0 };
        CGGradientRef gradient = CGGradientCreateWithColors(space, (__bridge CFArrayRef) colors, locations);
        CGContextDrawLinearGradient(context, gradient, CGPointMake(width, height), CGPointMake(0, 0), 0);
    } else if ([colorCode isEqualToString:@"gray_gradual"]) {
　　　　 //灰色渐变
        CGColorRef startColor = [UIColor colorWithRed:157/255.f green:157/255.f blue:157/255.f alpha:1].CGColor;
        CGColorRef endColor = [UIColor whiteColor].CGColor;
        NSArray *colors = @[(__bridge id)startColor,(__bridge id)endColor];
        CGFloat locations[] = { 0.0, 1.0 };
        CGGradientRef gradient = CGGradientCreateWithColors(space, (__bridge CFArrayRef) colors, locations);
        CGContextDrawLinearGradient(context, gradient, CGPointMake(width, height), CGPointMake(0, 0), 0);
    }

    CGContextDrawImage(context, CGRectMake(0, 0, width, height), cgimage);
    cgimage = CGBitmapContextCreateImage(context);
    
    self.singleImage = [UIImage imageWithCGImage:cgimage];
    self.printImage = [self createPrintPhotoWithImage:self.singleImage];
    
    NSData *data1 = UIImagePNGRepresentation(self.singleImage);
    [data1 writeToFile:[NSString stringWithFormat:@"证件照/%ld.png",time(NULL)] atomically:YES];
}

方法二：

int main(int argc, char * argv[]) {
    @autoreleasepool {
        UIImage *ig = [UIImage imageWithContentsOfFile:@"/Users/friday/Documents/MyGitHub/ImgMating/drawimg/ef038050d196e37752e2f57e2c042acc.png"];
        
        
        
        CGImageRef cgImg = ig.CGImage;
        
        
        
        CGDataProviderRef dataRef = CGImageGetDataProvider(cgImg);
        
        CFDataRef data = CGDataProviderCopyData(dataRef);
        CGDataProviderRelease(dataRef);
        
        NSData * data1 = (NSData *)CFBridgingRelease(data);
        
        Byte   *bitmapData = data1.bytes;
        
        int width = CGImageGetWidth(cgImg);
        int height = CGImageGetHeight(cgImg);
        int bitsPerComponent = CGImageGetBitsPerComponent(cgImg);
        int bitsPerPixel = CGImageGetBitsPerPixel(cgImg);
        int bytesPerRow = CGImageGetBytesPerRow(cgImg);
        CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(cgImg);
        
        CGDataProviderRef provider = CGDataProviderCreateWithCFData((CFDataRef)data1);
        CGFloat *decode = CGImageGetDecode(cgImg);
        bool shouldInterpolate=   CGImageGetShouldInterpolate(cgImg);
        CGColorRenderingIntent intent = CGImageGetRenderingIntent(cgImg);
        int dataLength = height * bytesPerRow;
        
        
        
        unsigned char *pByte = (unsigned char *)bitmapData;
        //    Result  = subview * subview.alpha + superView *superView.alpha * (1 - subview.alhpa)
        float superViewAlpha = 1.0;
        int   superView      = 0xff000000;
        
        int   cutValue       = 0xffffff00;
        int   resultCutValue = 0x000000ff;
        
        
        // 渐变色
        
        Byte red = 0xff;
        Byte red1 = 0x00;
        
        Byte green = 0x00;
        Byte green1 = 0xff;
        
        Byte blue = 0x00;
        Byte blue1 = 0x00;
        
        
        float redPer = (red1-red)/(float)height;
        float greenPer = (green1-green)/(float)height;
        float bluePer = (blue1-blue)/(float)height;
        
        for (int i = 0 ; i< dataLength; i+=4) {
            
            int row = i/bytesPerRow;
            
            float subviewAlpha = pByte[i+3]/255.0; // alpha;
            
            float cuRed = row*redPer+red;
            float cuGreen = row*greenPer+green;
            float cuBlue = row*bluePer+blue;
            pByte[i]   = pByte[i]*subviewAlpha + cuRed*superViewAlpha*(1-subviewAlpha);//red
            pByte[i+1] = pByte[i+1]*subviewAlpha+ cuGreen*superViewAlpha*(1-subviewAlpha);// green
            pByte[i+2] = pByte[i+2]*subviewAlpha + cuBlue*superViewAlpha*(1-subviewAlpha);// blue
            
            pByte[i+3] = 255;
            
        }
        
        
        
        CGImageRef newImg = CGImageCreate(width, height,  bitsPerComponent,  bitsPerPixel,  bytesPerRow, CGColorSpaceCreateDeviceRGB(),  bitmapInfo,    provider, decode,  shouldInterpolate,  intent);
        
        
        
        UIImage *svImg = [[UIImage alloc]initWithCGImage:newImg];
        
        NSData *data2 = UIImagePNGRepresentation(svImg);
        [data2 writeToFile:@"证件照.png" atomically:YES];
        
        
        return 1;
    }
}