Cocoa，Objective-C如何调整PNG图像的大小？

Question

Cocoa，Objective-C如何调整PNG图像的大小？

5

我是cocoa的新手，我想要做的是调整NSImage的大小，但是看起来我做错了什么，因为我的图像没有被调整大小。我查看了其他问题，并且这种方法看起来应该可以工作：

- (void)scaleIcons:(NSString *)outputPath{
NSImage *anImage;
NSSize imageSize;
NSString *finalPath;

anImage = [self image];

imageSize = [anImage size];
imageSize.width = 512;
imageSize.height = 512;
[anImage setSize:imageSize];

finalPath = [outputPath stringByAppendingString:@"/icon_512x512.png"];

NSData *imageData = [anImage TIFFRepresentation];
NSBitmapImageRep *rep = [NSBitmapImageRep imageRepWithData:imageData];
NSData *dataToWrite = [rep representationUsingType:NSPNGFileType properties:nil];
[dataToWrite writeToFile:finalPath atomically:NO];
}

一切都正常，唯独我的图片没有被缩放。有人可以帮忙吗？

- Rokas

3个回答

2

关于Parag Bafna的回答，对于调整大小应该使用“重新采样”而不是“裁剪”：

sips --resampleHeightWidth 10 10 input.png --out output.png

- Soul Clinic

0

您还可以使用sips（可脚本化图像处理系统）命令。

sips --cropToHeightWidth 10 10 input.png --out output.png

- Parag Bafna

那个命令的名称暗示它会裁剪图像（修剪不在所选区域内的像素），而不是调整大小。 - Duncan C

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- isaac · Accepted Answer

所以你的代码片段忽略了实际需要进行缩放/转换图像的操作。在尝试保存图像之前，请通过此方法将图像传递处理一下:

- (NSImage *)scaleImage:(NSImage *)image toSize:(NSSize)targetSize
{
  if ([image isValid])
  {
    NSSize imageSize = [image size];
    float width  = imageSize.width;
    float height = imageSize.height;
    float targetWidth  = targetSize.width;
    float targetHeight = targetSize.height;
    float scaleFactor  = 0.0;
    float scaledWidth  = targetWidth;
    float scaledHeight = targetHeight;

    NSPoint thumbnailPoint = NSZeroPoint;

    if (!NSEqualSizes(imageSize, targetSize))
    {
      float widthFactor  = targetWidth / width;
      float heightFactor = targetHeight / height;

      if (widthFactor < heightFactor)
      {
        scaleFactor = widthFactor;
      }
      else
      {
        scaleFactor = heightFactor;
      }

      scaledWidth  = width  * scaleFactor;
      scaledHeight = height * scaleFactor;

      if (widthFactor < heightFactor)
      {
        thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;
      }

      else if (widthFactor > heightFactor)
      {
        thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;
      }

    NSImage *newImage = [[NSImage alloc] initWithSize:targetSize];

    [newImage lockFocus];

     NSRect thumbnailRect;
     thumbnailRect.origin = thumbnailPoint;
     thumbnailRect.size.width = scaledWidth;
     thumbnailRect.size.height = scaledHeight;

     [image drawInRect:thumbnailRect
              fromRect:NSZeroRect
             operation:NSCompositeSourceOver
              fraction:1.0];

    [newImage unlockFocus];
  }

  return newImage;
}

如果您将此集成到现有的方法中:

- (void)scaleIcons:(NSString *)outputPath{

    NSSize outputSize = NSMakeSize(512.0f,512.0f);
    NSImage *anImage  = [self scaleImage:[self image] toSize:outputSize];

    NSString *finalPath = [outputPath stringByAppendingString:@"/icon_512x512.png"];
    NSData *imageData = [anImage TIFFRepresentation];
    NSBitmapImageRep *rep = [NSBitmapImageRep imageRepWithData:imageData];
    NSData *dataToWrite = [rep representationUsingType:NSPNGFileType properties:nil];
   [dataToWrite writeToFile:finalPath atomically:NO];
}