Question

所以我有许多带有白色背景的jpg图像，我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。我有一个功能，但它会导致每个图像周围出现锯齿状边缘。有没有办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。

以下是一个例子：

该方法还会删除图像中接近白色的额外像素：

我认为理想的方法会改变白色像素的alpha值，因为它们接近纯白色而不是仅仅将它们全部移除。任何想法都将不胜感激。

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？使用下面的代码。

- (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

目标C：如何从JPG图像中删除白色背景而不会丢失边缘质量

1 个答案: