适用于iOS的Luma Key(从图像创建alpha蒙版)

Question

我正在构建一个应用程序,允许人们在白色背景上上传自己的图像,该应用程序将创建一个人的轮廓.

我很难找出背景.我正在使用GPUImage框架和GPUImageChromaKeyBlendFilter作品非常适合颜色,但如果你得到白色/黑色,很难键出其中一种颜色.如果我将键设置为白色或黑色,则键入相同的键.

有什么建议？

Answer 1

因此，要将白色更改为透明，我们可以使用以下方法：

-(UIImage *)changeWhiteColorTransparent: (UIImage *)image {
    CGImageRef rawImageRef=image.CGImage;

    const float colorMasking[6] = {222, 255, 222, 255, 222, 255};

    UIGraphicsBeginImageContext(image.size);
    CGImageRef maskedImageRef=CGImageCreateWithMaskingColors(rawImageRef, colorMasking);
    {
        //if in iphone
        CGContextTranslateCTM(UIGraphicsGetCurrentContext(), 0.0, image.size.height);
        CGContextScaleCTM(UIGraphicsGetCurrentContext(), 1.0, -1.0); 
    }

    CGContextDrawImage(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, image.size.width, image.size.height), maskedImageRef);
    UIImage *result = UIGraphicsGetImageFromCurrentImageContext();
    CGImageRelease(maskedImageRef);
    UIGraphicsEndImageContext();    
    return result;
}

并将非透明像素替换为黑色，我们可以使用：

- (UIImage *) changeColor: (UIImage *)image {
    UIGraphicsBeginImageContext(image.size);

    CGRect contextRect;
    contextRect.origin.x = 0.0f;
    contextRect.origin.y = 0.0f;
    contextRect.size = [image size];
    // Retrieve source image and begin image context
    CGSize itemImageSize = [image size];
    CGPoint itemImagePosition;
    itemImagePosition.x = ceilf((contextRect.size.width - itemImageSize.width) / 2);
    itemImagePosition.y = ceilf((contextRect.size.height - itemImageSize.height) );

    UIGraphicsBeginImageContext(contextRect.size);

    CGContextRef c = UIGraphicsGetCurrentContext();
    // Setup shadow
    // Setup transparency layer and clip to mask
    CGContextBeginTransparencyLayer(c, NULL);
    CGContextScaleCTM(c, 1.0, -1.0);
    CGContextClipToMask(c, CGRectMake(itemImagePosition.x, -itemImagePosition.y, itemImageSize.width, -itemImageSize.height), [image CGImage]);

    CGContextSetFillColorWithColor(c, [UIColor blackColor].CGColor);


    contextRect.size.height = -contextRect.size.height;
    contextRect.size.height -= 15;
    // Fill and end the transparency layer
    CGContextFillRect(c, contextRect);
    CGContextEndTransparencyLayer(c);

    UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return img;
}

所以实际上这将是：

-(UIImage *)silhouetteForImage:(UIImage *)img {
    return [self changeColour:[self changeWhiteColorTransparent:img]];
}

显然，您会在后台线程中调用它，以保持一切顺利运行。