Objective-c - 获取图像中最少使用和最多使用的颜色

Question

我试图从音乐播放应用程序的 MP3 文件的专辑插图中获取最少使用的颜色和最常用的颜色。我需要颜色来做像新 itunes 11 那样的效果。菜单的背景颜色是最常用的颜色，最少使用的颜色是歌曲标签和艺术家姓名的颜色。我正在使用

`- (UIColor*) getPixelColorAtLocation:(CGPoint)point {
    UIColor* color = nil;
    CGImageRef inImage = self.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));
        int 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 = CGColorSpaceCreateWithName(kCGColorSpaceGenericRGB);
    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;
}`

获取图像底部的颜色，使其在我的 View Controller 中混合，该 View Controller 使用该颜色作为背景，并有一个阴影使其混合。

问题:所以，正如它所说:如何从图像中获取最少和最多使用的颜色？

Answer 1

下面的方法按照以下步骤拍摄图像并分析其主要颜色:

1.) 缩小图像并确定主要像素颜色。

2.) 添加一些颜色灵 active 以允许缩放期间的损失

3.) 区分颜色，去除相似的颜色

4.) 以有序数组或百分比的形式返回颜色

您可以调整它以返回特定数量的颜色，例如如果您需要返回保证数量的颜色，则使用图像中的前 10 种颜色，或者如果不需要，则只使用“detail”变量。

较大的图像需要很长时间才能进行高细节分析。

毫无疑问，该方法可以稍微清理一下，但可能是一个很好的起点。

像这样使用:

 NSDictionary * mainColours = [s mainColoursInImage:image detail:1];

-(NSDictionary*)mainColoursInImage:(UIImage *)image detail:(int)detail {

//1. determine detail vars (0==low,1==default,2==high)
//default detail
float dimension = 10;
float flexibility = 2;
float range = 60;

//low detail
if (detail==0){
    dimension = 4;
    flexibility = 1;
    range = 100;

//high detail (patience!)
} else if (detail==2){
    dimension = 100;
    flexibility = 10;
    range = 20;
}

//2. determine the colours in the image
NSMutableArray * colours = [NSMutableArray new];
CGImageRef imageRef = [image CGImage];
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
unsigned char *rawData = (unsigned char*) calloc(dimension * dimension * 4, sizeof(unsigned char));
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * dimension;
NSUInteger bitsPerComponent = 8;
CGContextRef context = CGBitmapContextCreate(rawData, dimension, dimension, bitsPerComponent, bytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colorSpace);
CGContextDrawImage(context, CGRectMake(0, 0, dimension, dimension), imageRef);
CGContextRelease(context);

float x = 0;
float y = 0;
for (int n = 0; n<(dimension*dimension); n++){

    int index = (bytesPerRow * y) + x * bytesPerPixel;
    int red   = rawData[index];
    int green = rawData[index + 1];
    int blue  = rawData[index + 2];
    int alpha = rawData[index + 3];
    NSArray * a = [NSArray arrayWithObjects:[NSString stringWithFormat:@"%i",red],[NSString stringWithFormat:@"%i",green],[NSString stringWithFormat:@"%i",blue],[NSString stringWithFormat:@"%i",alpha], nil];
    [colours addObject:a];

    y++;
    if (y==dimension){
        y=0;
        x++;
    }
}
free(rawData);

//3. add some colour flexibility (adds more colours either side of the colours in the image)
NSArray * copyColours = [NSArray arrayWithArray:colours];
NSMutableArray * flexibleColours = [NSMutableArray new];

float flexFactor = flexibility * 2 + 1;
float factor = flexFactor * flexFactor * 3; //(r,g,b) == *3
for (int n = 0; n<(dimension * dimension); n++){

    NSArray * pixelColours = copyColours[n];
    NSMutableArray * reds = [NSMutableArray new];
    NSMutableArray * greens = [NSMutableArray new];
    NSMutableArray * blues = [NSMutableArray new];

    for (int p = 0; p<3; p++){

        NSString * rgbStr = pixelColours[p];
        int rgb = [rgbStr intValue];

        for (int f = -flexibility; f<flexibility+1; f++){
            int newRGB = rgb+f;
            if (newRGB<0){
                newRGB = 0;
            }
            if (p==0){
                [reds addObject:[NSString stringWithFormat:@"%i",newRGB]];
            } else if (p==1){
                [greens addObject:[NSString stringWithFormat:@"%i",newRGB]];
            } else if (p==2){
                [blues addObject:[NSString stringWithFormat:@"%i",newRGB]];
            }
        }
    }

    int r = 0;
    int g = 0;
    int b = 0;
    for (int k = 0; k<factor; k++){

        int red = [reds[r] intValue];
        int green = [greens[g] intValue];
        int blue = [blues[b] intValue];

        NSString * rgbString = [NSString stringWithFormat:@"%i,%i,%i",red,green,blue];
        [flexibleColours addObject:rgbString];

        b++;
        if (b==flexFactor){ b=0; g++; }
        if (g==flexFactor){ g=0; r++; }
    }
}

//4. distinguish the colours
//orders the flexible colours by their occurrence
//then keeps them if they are sufficiently disimilar

NSMutableDictionary * colourCounter = [NSMutableDictionary new];

//count the occurences in the array
NSCountedSet *countedSet = [[NSCountedSet alloc] initWithArray:flexibleColours];
for (NSString *item in countedSet) {
    NSUInteger count = [countedSet countForObject:item];
    [colourCounter setValue:[NSNumber numberWithInteger:count] forKey:item];
}

//sort keys highest occurrence to lowest
NSArray *orderedKeys = [colourCounter keysSortedByValueUsingComparator:^NSComparisonResult(id obj1, id obj2){
    return [obj2 compare:obj1];
}];

//checks if the colour is similar to another one already included
NSMutableArray * ranges = [NSMutableArray new];
for (NSString * key in orderedKeys){
    NSArray * rgb = [key componentsSeparatedByString:@","];
    int r = [rgb[0] intValue];
    int g = [rgb[1] intValue];
    int b = [rgb[2] intValue];
    bool exclude = false;
    for (NSString * ranged_key in ranges){
        NSArray * ranged_rgb = [ranged_key componentsSeparatedByString:@","];

        int ranged_r = [ranged_rgb[0] intValue];
        int ranged_g = [ranged_rgb[1] intValue];
        int ranged_b = [ranged_rgb[2] intValue];

        if (r>= ranged_r-range && r<= ranged_r+range){
            if (g>= ranged_g-range && g<= ranged_g+range){
                if (b>= ranged_b-range && b<= ranged_b+range){
                    exclude = true;
                }
            }
        }
    }

    if (!exclude){ [ranges addObject:key]; }
}

//return ranges array here if you just want the ordered colours high to low
NSMutableArray * colourArray = [NSMutableArray new];
for (NSString * key in ranges){
    NSArray * rgb = [key componentsSeparatedByString:@","];
    float r = [rgb[0] floatValue];
    float g = [rgb[1] floatValue];
    float b = [rgb[2] floatValue];
    UIColor * colour = [UIColor colorWithRed:(r/255.0f) green:(g/255.0f) blue:(b/255.0f) alpha:1.0f];
    [colourArray addObject:colour];
}

//if you just want an array of images of most common to least, return here
//return [NSDictionary dictionaryWithObject:colourArray forKey:@"colours"];


//if you want percentages to colours continue below
NSMutableDictionary * temp = [NSMutableDictionary new];
float totalCount = 0.0f;
for (NSString * rangeKey in ranges){
    NSNumber * count = colourCounter[rangeKey];
    totalCount += [count intValue];
    temp[rangeKey]=count;
}

//set percentages
NSMutableDictionary * colourDictionary = [NSMutableDictionary new];
for (NSString * key in temp){
    float count = [temp[key] floatValue];
    float percentage = count/totalCount;
    NSArray * rgb = [key componentsSeparatedByString:@","];
    float r = [rgb[0] floatValue];
    float g = [rgb[1] floatValue];
    float b = [rgb[2] floatValue];
    UIColor * colour = [UIColor colorWithRed:(r/255.0f) green:(g/255.0f) blue:(b/255.0f) alpha:1.0f];
    colourDictionary[colour]=[NSNumber numberWithFloat:percentage];
}

return colourDictionary;

}