Save image after rotate it. But picture has lower resolution after saving

Question

I am trying rotate an image from IKImageView. But after rotating and saving it, I got a lower resolution picture.
Below is code which I am using for rotating

-(NSImage *)imageRotated:(float)degrees{
    degrees = fmod(degrees, 360.);
    if(0 == degrees){
        return self;
    }
    NSSize size = [self size];
    NSSize maxSize;
    if(90. == degrees || 270. == degrees || -90== degrees || -270. == degrees){
        maxSize = NSMakeSize(size.height, size.width);
    }else if (180. == degrees || -180. == degrees){
        maxSize = size;
    }else{
        maxSize = NSMakeSize(20+MAX(size.width, size.height), 20+MAX(size.width, size.height));
    }

    NSAffineTransform *rot = [NSAffineTransform transform];
    [rot rotateByDegrees:degrees];
    NSAffineTransform *center = [ NSAffineTransform transform];
    [center translateXBy:maxSize.width/2 yBy:maxSize.height/2];
    [rot appendTransform:center];
    NSImage *image = [[NSImage alloc]init];
    image = [NSImage imageWithSize:maxSize flipped:NO drawingHandler:^BOOL(NSRect desRect){
            [rot concat];
            NSRect rect = NSMakeRect(0, 0, size.width, size.height);
            NSPoint corner = NSMakePoint(-size.width/2, -size.height/2);
            [self drawAtPoint:corner fromRect:rect operation:NSCompositeCopy fraction:1.0];
        return YES;
    }];
    return image;
}

then, I converted image to bitmap by below code

- (NSBitmapImageRep *)bitmapImageRepresentation{
    int width = [self size].width;
    int height = [self size].height;

    if(width <1 || height < 1)
        return nil;

    NSBitmapImageRep *rep = [[NSBitmapImageRep alloc]
                             initWithBitmapDataPlanes:NULL
                             pixelsWide:width
                             pixelsHigh:height
                             bitsPerSample:8
                             samplesPerPixel:4
                             hasAlpha:YES
                             isPlanar:NO
                             colorSpaceName:NSDeviceRGBColorSpace
                             bytesPerRow:width*4
                             bitsPerPixel:32];

    NSGraphicsContext *ctx = [NSGraphicsContext graphicsContextWithBitmapImageRep:rep];
    [NSGraphicsContext saveGraphicsState];
    [NSGraphicsContext setCurrentContext:ctx];
    [self drawAtPoint:NSZeroPoint fromRect:NSZeroRect operation:NSCompositeCopy fraction:1.0];
    [ctx flushGraphics];
    [NSGraphicsContext restoreGraphicsState];
    return rep;
}

and I used below code to convert to NSData, then write to file

- (NSData*)toNSData{
    NSImage *imgTemp = [[NSImage alloc]initWithSize:NSMakeSize(self.size.width*2, self.size.height*2)];
    imgTemp = self;
    NSBitmapImageRep *bmprep = [imgTemp bitmapImageRepresentation];
    NSDictionary *imageProps = [NSDictionary dictionaryWithObject:[NSNumber numberWithFloat:1.0] forKey:NSImageCurrentFrame];
    NSData *pngData = [[NSData alloc]init];
    pngData = [bmprep representationUsingType:NSPNGFileType properties:imageProps];
    return pngData;
}

Could you show me the reason why picture after saving have lower resolution?.
I am using MacBook Pro (Retina, 13-inch, Mid 2014)
Thank you very much in advance :)

What is the issue? The image after save is rotated. Isn't that what you want? — FightOn, Aug 07 '17 at 19:22
@FightOn: Hello, thank you for your feedback in advance. I updated my question again. Could you help me check it again? — NextTrang, Aug 17 '17 at 03:30

score 0 · Accepted Answer · answered Aug 07 '17 at 08:03

0

I think you are rotating the image twice.

Inside the method rotateLeft

//First rotation
//Rotate Picture
        Img = [self imageRotatedByDegrees:Img and:90];

//Second rotation
[_imageView rotateImageLeft:sender];

So I believe you will need to block the second rotation and you will get rid of your issue.

answered Aug 07 '17 at 08:03

Paras Gorasiya

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Thank you for your answer, it is so usefull for me. Currently, I am facing with a other problem. That is the resolution of image decreased after saving. I updated my question, Could you help me check it again – NextTrang Aug 17 '17 at 03:34
It seems like in your updated question it is totally different code than I remember, so I would advise you to ask a separate question in order to get help from more people. Also dont forget to accept and upvote the answer if it solved your issue, that helps understanding the problem better for us. Thanks – Paras Gorasiya Aug 17 '17 at 03:40

Save image after rotate it. But picture has lower resolution after saving

1 Answers1