如何改变目标c中的图像分辨率 [英] how to change image resolution in objective-c

问题描述

我需要更改objective-c中现有图像的分辨率，就像Apple的预览应用工具 - >调整大小...->分辨率。

请让我知道可能的解决方案。

解决方案

这里有一个很好的例子我使用 - http://weblog.scifihifi.com/2005/06/25/how-to-resize-an-nsimage/

从该示例中，您可以将resizedData写入文件 - 这将是tiff格式的调整大小的输出。

UPDATE：

这里是NSImage类别实现，允许使用指定的DPI保存NSImage实例：

$ （NSBitmapImageFileType）imageType withDPI：（CGFloat）dpiValue atPath：（NSString *）filePath;（b）
@end

@implementation NSImage（DPIHelper）


- （void）saveAsImageType：（NSBitmapImageFileType）imageType withDPI：（CGFloat）dpiValue atPath： （NSString *）filePath
{
NSBitmapImageRep * rep = [[self representations] objectAtIndex：0];

NSSize pointsSize = rep.size;
NSSize pixelSize = NSMakeSize（rep.pixelsWide，rep.pixelsHigh）;

CGFloat currentDPI = ceilf（（72.0f * pixelSize.width）/pointsSize.width）;
NSLog（@current DPI％f，currentDPI）;

NSSize updatedPointsSize = pointsSize;

updatedPointsSize.width = ceilf（（72.0f * pixelSize.width）/ dpiValue）;
updatedPointsSize.height = ceilf（（72.0f * pixelSize.height）/ dpiValue）;

[rep setSize：updatedPointsSize];

NSData * data = [rep representationUsingType：imageType properties：nil];
[data writeToFile：filePath atomically：NO];

}

@end

使用它像这样：

  NSImage * theImage2 = [NSImage imageNamed：@image.jpg]; 
 [theImage2 saveAsImageType：NSJPEGFileType withDPI：36.0f atPath：@/ Users /< user-name> /image-updated.jpg]; 
  

I need to change the resolution of the existing image in objective-c just like Apple's Preview application Tools->Adjust Size...->Resolution.

Please let me know the possible solutions.

解决方案

Here's a great sample I've used - http://weblog.scifihifi.com/2005/06/25/how-to-resize-an-nsimage/

From that sample, you can write resizedData to the file - and this will be a resized output in tiff format.

UPDATE:

here comes the NSImage category implementation, that allows to save NSImage instance with specified DPI:

@interface NSImage (DPIHelper)
- (void) saveAsImageType: (NSBitmapImageFileType) imageType withDPI: (CGFloat) dpiValue atPath: (NSString *) filePath;
@end

@implementation NSImage (DPIHelper)


- (void) saveAsImageType: (NSBitmapImageFileType) imageType withDPI: (CGFloat) dpiValue atPath: (NSString *) filePath
{
  NSBitmapImageRep *rep = [[self representations] objectAtIndex: 0];

  NSSize pointsSize = rep.size;
  NSSize pixelSize = NSMakeSize(rep.pixelsWide, rep.pixelsHigh);

  CGFloat currentDPI = ceilf((72.0f * pixelSize.width)/pointsSize.width);
  NSLog(@"current DPI %f", currentDPI);

  NSSize updatedPointsSize = pointsSize;

  updatedPointsSize.width = ceilf((72.0f * pixelSize.width)/dpiValue);
  updatedPointsSize.height = ceilf((72.0f * pixelSize.height)/dpiValue);

  [rep setSize:updatedPointsSize];

  NSData *data = [rep representationUsingType: imageType properties: nil];
  [data writeToFile: filePath atomically: NO];

}

@end

you can use it like this:

NSImage *theImage2 = [NSImage imageNamed:@"image.jpg"];
[theImage2 saveAsImageType:NSJPEGFileType withDPI: 36.0f atPath: @"/Users/<user-name>/image-updated.jpg"];

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