iOS开发-简单图片背景替换(实现抠图效果)

之前好奇, 想实现这样的功能   -----> iOS图像处理-(jpg去除白色背景)

把一张图片（.jpg）的白色背景抠掉，转成.png 格式的有alpha通道的透明图。

然后在论坛，得到了想要的答案。这里先谢过那位大牛, 也提供了参考资料:  iOS8 Core Image In Swift：更复杂的滤镜

然后今天, 自己也总结一下。

写了个小小的demo, 实现背景图片的切换. 效果如下:

可以看到, 原先的黄色渐变背景被替换掉了。  接下去就是要实现这样一个功能。

当然. 如果感兴趣, 你可以从这里下载到源码: http://download.csdn.net/detail/hitwhylz/8186081

struct CubeMap {
    int length;
    float dimension;
    float *data;
};

struct CubeMap createCubeMap(float minHueAngle, float maxHueAngle) {
    const unsigned int size = 64;
    struct CubeMap map;
    map.length = size * size * size * sizeof (float) * 4;
    map.dimension = size;
    float *cubeData = (float *)malloc (map.length);
    float rgb[3], hsv[3], *c = cubeData;
    
    for (int z = 0; z < size; z++){
        rgb[2] = ((double)z)/(size-1); // Blue value
        for (int y = 0; y < size; y++){
            rgb[1] = ((double)y)/(size-1); // Green value
            for (int x = 0; x < size; x ++){
                rgb[0] = ((double)x)/(size-1); // Red value
                rgbToHSV(rgb,hsv);
                // Use the hue value to determine which to make transparent
                // The minimum and maximum hue angle depends on
                // the color you want to remove
                float alpha = (hsv[0] > minHueAngle && hsv[0] < maxHueAngle) ? 0.0f: 1.0f;
                // Calculate premultiplied alpha values for the cube
                c[0] = rgb[0] * alpha;
                c[1] = rgb[1] * alpha;
                c[2] = rgb[2] * alpha;
                c[3] = alpha;
                c += 4; // advance our pointer into memory for the next color value
            }
        }
    }
    map.data = cubeData;
    return map;
}

我将这个方法稍微改造了一下，选择一个结构体，因为外面要用到length和dimension。苹果没有提供rgbToHSV方法的实现，可以用我找到的这个：

void rgbToHSV(float *rgb, float *hsv) {
    float min, max, delta;
    float r = rgb[0], g = rgb[1], b = rgb[2];
    float *h = hsv, *s = hsv + 1, *v = hsv + 2;
    
    min = fmin(fmin(r, g), b );
    max = fmax(fmax(r, g), b );
    *v = max;
    delta = max - min;
    if( max != 0 )
        *s = delta / max;
    else {
        *s = 0;
        *h = -1;
        return;
    }
    if( r == max )
        *h = ( g - b ) / delta;
    else if( g == max )
        *h = 2 + ( b - r ) / delta;
    else
        *h = 4 + ( r - g ) / delta;
    *h *= 60;
    if( *h < 0 )
        *h += 360;
}

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

使用这个文件的时候, 需要把调用方, 比如我这里的ViewController.m 改为 ViewController.mm 

这样就能支持c文件。 然后导入头文件 #include "cubeMap.c"

之后就是简单的调用了, 具体参加如下代码:

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    
    
    //size  600?×?450
    
    //显示原图片
    UILabel *oldLabel = [[UILabel alloc]initWithFrame:CGRectMake(0, 65, 160, 15)];
    oldLabel.text = @"原图";
    oldLabel.textAlignment = NSTextAlignmentCenter;
    [self.view addSubview:oldLabel];
    
    UIImageView *oldImageView = [[UIImageView alloc]initWithFrame:CGRectMake(5, 80, 150, 112)];
    oldImageView.image = [UIImage imageNamed:@"beautyPic.jpg"];
    [self.view addSubview:oldImageView];
    
    //显示背景图片
    UILabel *backLabel = [[UILabel alloc]initWithFrame:CGRectMake(160, 65, 160, 15)];
    backLabel.text = @"背景图";
    backLabel.textAlignment = NSTextAlignmentCenter;
    [self.view addSubview:backLabel];
    
    UIImageView *backImageView = [[UIImageView alloc]initWithFrame:CGRectMake(165, 80, 150, 112)];
    backImageView.image = [UIImage imageNamed:@"background"];
    [self.view addSubview:backImageView];
    
    
    
    //更换背景图片
    CubeMap myCube = createCubeMap(35, 55);
    NSData *myData = [[NSData alloc]initWithBytesNoCopy:myCube.data length:myCube.length freeWhenDone:true];
    CIFilter *colorCubeFilter = [CIFilter filterWithName:@"CIColorCube"];
    [colorCubeFilter setValue:[NSNumber numberWithFloat:myCube.dimension] forKey:@"inputCubeDimension"];
    [colorCubeFilter setValue:myData forKey:@"inputCubeData"];
    [colorCubeFilter setValue:[CIImage imageWithCGImage:oldImageView.image.CGImage] forKey:kCIInputImageKey];

    CIImage *outputImage = colorCubeFilter.outputImage;
    
    CIFilter *sourceOverCompositingFilter = [CIFilter filterWithName:@"CISourceOverCompositing"];
    [sourceOverCompositingFilter setValue:outputImage forKey:kCIInputImageKey];
    [sourceOverCompositingFilter setValue:[CIImage imageWithCGImage:backImageView.image.CGImage] forKey:kCIInputBackgroundImageKey];
    
    outputImage = sourceOverCompositingFilter.outputImage;
    CGImage *cgImage = [[CIContext contextWithOptions: nil]createCGImage:outputImage fromRect:outputImage.extent];
    
    UILabel *newLabel = [[UILabel alloc]initWithFrame:CGRectMake(0, 200, 320, 15)];
    newLabel.text = @"合成图";
    newLabel.textAlignment = NSTextAlignmentCenter;
    [self.view addSubview:newLabel];
    
    
    UIImageView *newImageView = [[UIImageView alloc]initWithFrame:CGRectMake(10, 220, 300, 225)];
    newImageView.image = [UIImage imageWithCGImage:cgImage];
    [self.view addSubview:newImageView];
    
}