ios - Objective-C : How to remove a white background from a JPG image without losing edge quality

Question

所以我有许多白色背景的 jpg 图像正在加载到我的应用程序中，我想以编程方式删除白色背景。我有一个函数可以执行此操作，但它会导致每个图像周围出现一些锯齿状边缘。有没有一种方法可以混合这些边缘以获得平滑的边缘？

我目前的方法:

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

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

    UIGraphicsBeginImageContextWithOptions(image.size, NO, [UIScreen mainScreen].scale);
    CGImageRef maskedImageRef=CGImageCreateWithMaskingColors(rawImageRef, colorMasking);

    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;
}

我知道我可以更改颜色屏蔽值，但我认为任何组合都不会产生没有白色背景的平滑图片。

举个例子:

该方法还会删除图像中接近白色的额外像素:

我认为理想的方法是根据它们与纯白色的接近程度来改变白色像素的 alpha，而不是将它们全部移除。任何想法将不胜感激。

Answer 1

#import "UIImage+FloodFill.h"
//https://github.com/Chintan-Dave/UIImageScanlineFloodfill

#define Mask8(x) ( (x) & 0xFF )
#define R(x) ( Mask8(x) )
#define G(x) ( Mask8(x >> 8 ) )
#define B(x) ( Mask8(x >> 16) )
#define A(x) ( Mask8(x >> 24) )
#define RGBAMake(r, g, b, a) ( Mask8(r) | Mask8(g) << 8 | Mask8(b) << 16 | Mask8(a) << 24 )

@interface UIImage (BackgroundRemoval)
//Simple Removal
- (UIImage *)floodFillRemoveBackgroundColor;
@end

@implementation UIImage (BackgroundRemoval)
- (UIImage*) maskImageWithMask:(UIImage *)maskImage {
  CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

  CGImageRef maskImageRef = [maskImage CGImage];

  // create a bitmap graphics context the size of the image
  CGContextRef mainViewContentContext = CGBitmapContextCreate (NULL, maskImage.size.width, maskImage.size.height, 8, 0, colorSpace, (CGBitmapInfo)kCGImageAlphaPremultipliedLast);
  CGColorSpaceRelease(colorSpace);

  if (mainViewContentContext==NULL)
  return NULL;

  CGFloat ratio = 0;

  ratio = maskImage.size.width/ self.size.width;

  if(ratio * self.size.height < maskImage.size.height) {
    ratio = maskImage.size.height/ self.size.height;
  }

  CGRect rect1  = { {0, 0}, {maskImage.size.width, maskImage.size.height} };
  CGRect rect2  = { {-((self.size.width*ratio)-maskImage.size.width)/2 , -((self.size.height*ratio)-maskImage.size.height)/2}, {self.size.width*ratio, self.size.height*ratio} };


  CGContextClipToMask(mainViewContentContext, rect1, maskImageRef);
  CGContextDrawImage(mainViewContentContext, rect2, self.CGImage);


  // Create CGImageRef of the main view bitmap content, and then
  // release that bitmap context
  CGImageRef newImage = CGBitmapContextCreateImage(mainViewContentContext);
  CGContextRelease(mainViewContentContext);

  UIImage *theImage = [UIImage imageWithCGImage:newImage];

  CGImageRelease(newImage);

  // return the image
  return theImage;
}

- (UIImage *)floodFillRemove{
  //1
  UIImage *processedImage = [self floodFillFromPoint:CGPointMake(0, 0) withColor:[UIColor magentaColor] andTolerance:0];

  CGImageRef inputCGImage=processedImage.CGImage;
  UInt32 * inputPixels;
  NSUInteger inputWidth = CGImageGetWidth(inputCGImage);
  NSUInteger inputHeight = CGImageGetHeight(inputCGImage);

  CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

  NSUInteger bytesPerPixel = 4;
  NSUInteger bitsPerComponent = 8;

  NSUInteger inputBytesPerRow = bytesPerPixel * inputWidth;

  inputPixels = (UInt32 *)calloc(inputHeight * inputWidth, sizeof(UInt32));

  CGContextRef context = CGBitmapContextCreate(inputPixels, inputWidth, inputHeight, bitsPerComponent, inputBytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);

  CGContextDrawImage(context, CGRectMake(0, 0, inputWidth, inputHeight), inputCGImage);

  //2

  for (NSUInteger j = 0; j < inputHeight; j++) {
    for (NSUInteger i = 0; i < inputWidth; i++) {
      UInt32 * currentPixel = inputPixels + (j * inputWidth) + i;
      UInt32 color = *currentPixel;

      if (R(color) == 255 && G(color) == 0 && B(color) == 255) {
        *currentPixel = RGBAMake(0, 0, 0, A(0));
        }else{
          *currentPixel = RGBAMake(R(color), G(color), B(color), A(color));
        }
      }
  }
  CGImageRef newCGImage = CGBitmapContextCreateImage(context);

  //3

  UIImage * maskImage = [UIImage imageWithCGImage:newCGImage];
  CGColorSpaceRelease(colorSpace);
  CGContextRelease(context);
  free(inputPixels);

  UIImage *result = [self maskImageWithMask:maskImage];

  //4

  return result;
}

@end

如果您的图像具有渐变背景怎么办？为此使用以下代码。

- (UIImage *)complexReoveBackground{

  GPUImagePicture *stillImageSource = [[GPUImagePicture alloc] initWithImage:self];

  GPUImagePrewittEdgeDetectionFilter *filter = [[GPUImagePrewittEdgeDetectionFilter alloc] init];
  [filter setEdgeStrength:0.04];

  [stillImageSource addTarget:filter];
  [filter useNextFrameForImageCapture];
  [stillImageSource processImage];

  UIImage *resultImage = [filter imageFromCurrentFramebuffer];

  UIImage *processedImage = [resultImage floodFillFromPoint:CGPointMake(0, 0) withColor:[UIColor magentaColor] andTolerance:0];

  CGImageRef inputCGImage=processedImage.CGImage;
  UInt32 * inputPixels;
  NSUInteger inputWidth = CGImageGetWidth(inputCGImage);
  NSUInteger inputHeight = CGImageGetHeight(inputCGImage);

  CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

  NSUInteger bytesPerPixel = 4;
  NSUInteger bitsPerComponent = 8;

  NSUInteger inputBytesPerRow = bytesPerPixel * inputWidth;

  inputPixels = (UInt32 *)calloc(inputHeight * inputWidth, sizeof(UInt32));

  CGContextRef context = CGBitmapContextCreate(inputPixels, inputWidth, inputHeight, bitsPerComponent, inputBytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);

  CGContextDrawImage(context, CGRectMake(0, 0, inputWidth, inputHeight), inputCGImage);

  for (NSUInteger j = 0; j < inputHeight; j++) {
    for (NSUInteger i = 0; i < inputWidth; i++) {
      UInt32 * currentPixel = inputPixels + (j * inputWidth) + i;
      UInt32 color = *currentPixel;

      if (R(color) == 255 && G(color) == 0 &&   B(color) == 255) {
        *currentPixel = RGBAMake(0, 0, 0, A(0));
      }else{
        *currentPixel = RGBAMake(0, 0, 0, 255);
      }
    }
  }
  CGImageRef newCGImage = CGBitmapContextCreateImage(context);
  UIImage * maskImage = [UIImage imageWithCGImage:newCGImage];
  CGColorSpaceRelease(colorSpace);
  CGContextRelease(context);
  free(inputPixels);

  GPUImagePicture *maskImageSource = [[GPUImagePicture alloc] initWithImage:maskImage];

  GPUImageGaussianBlurFilter *blurFilter = [[GPUImageGaussianBlurFilter alloc] init];
  [blurFilter setBlurRadiusInPixels:0.7];
  [maskImageSource addTarget:blurFilter];
  [blurFilter useNextFrameForImageCapture];
  [maskImageSource processImage];

  UIImage *blurMaskImage = [blurFilter imageFromCurrentFramebuffer];
  //return blurMaskImage;
  UIImage *result = [self maskImageWithMask:blurMaskImage];

  return result;
}

您可以从此处下载示例代码 sample code