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.
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"];