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Apocalypse · Mar 18, 2002, 06:47 PM

Hello,

I was wondering if anyone knows if the Cocoa API has any methods for scaling NSImage data. I know that it can scale the display of the image data but I can't find anything that will scale the actual data. I might have overlooked something, though.

Seems like a tedious thing to do if someone else has already done it.

Thanks,
Jeff.

Rickster · Mar 19, 2002, 12:15 AM

<BLOCKQUOTE>code:<HR><pre>
NSImage *bigImage, *littleImage;

bigImage = [NSImage imageNamed:@"SomeBigImageInMyAppBundle"];
littleImage = [[NSImage alloc] initWithSize:NSMakeSize(32, 32)];
[littleImage lockFocus];
[bigImage drawInRect:NSMakeRect(0, 0, 32, 32) operation:NSCompositeCopy fraction:1.0];
[littleImage unlockFocus];
[/code]

This code is right off the top of my head, so it may not compile when copied/pasted.

If you want to save the finished iamge, call [littleImage TIFFRepresentation] to get an NSData you can write to a file. Also, you may want to mess with the current NSGraphicsContext's image interpolation factor after [littleImage lockFocus] so you get good scaling.

smeger · Mar 19, 2002, 12:33 AM

Ahhh, this is beautiful! I've been using the quicktime API for this and hating it (quicktime code is really nasty after you've gotten used to objective-c yumminess).

kongtomorrow · Mar 19, 2002, 03:49 AM

So that doesn't quite compile, it needs an extra argument, fromRect. My question is, how can I make an NSRect object which has the dimensions of the source image?

I'm sorry to be a pain, but I've wanted to be able to do this for a while and this got me excited. The information I need is surely contained in the NSSize object obtained from [bigImage size], but I don't know how to access it since it is a Java class! Or is it? I'm obviously new to objective-c, and seem to be quite confused.

Thanks to anyone who decides to help, and to Rick already!

[ 03-19-2002: Message edited by: kongtomorrow ]

[ 03-19-2002: Message edited by: kongtomorrow ]

[ 03-19-2002: Message edited by: kongtomorrow ]

kongtomorrow · Mar 19, 2002, 11:50 AM

I got what I wanted to work, but from inspection the scaling seems to be a simple resampling of the image. Does anyone know if a more sophisticated scaling algorithm is already implemented somewhere in the frameworks in a way we can get at it?

int69h · Mar 19, 2002, 10:40 PM

NSSize is a C structure declared in <Foundation/NSGeometry.h>
Here's the declaration:
<BLOCKQUOTE>code:<HR><pre>
typedef struct _NSSize {
float width; /* should never be negative */
float height; /* should never be negative */
} NSSize;
[/code]

Assuming you have a NSSize called mySize, you could access width like this:
<BLOCKQUOTE>code:<HR><pre>
myFloat = mySize.width;
[/code]

If you have an NSRect that you want to know the width of you could do

<BLOCKQUOTE>code:<HR><pre>
myFloat = myRect.size.width;
[/code]

or

<BLOCKQUOTE>code:<HR><pre>
myFloat = NSWidth(myRect);
[/code]

All of of this and more can be found at /System/Library/Frameworks/Foundation.framework/Headers/NSGeometry.h

I'm not exactly sure where you got the idea this was a java class, but I've heard stranger ideas.

Rickster · Mar 19, 2002, 10:42 PM

oops, yeah, I left out the fromRect parameter. But you don't need to come up with the dimensions of your image there... if you pass in NSZeroRect it will automatically use the entire image. (If you pass in anything else, it lets you grab a portion of the image.)

See NSGraphicsContext.h for how to change the image interpolation setting (which you should do immediately after locking focus on littleImage) if you'd like better smoothing of the scaled image.

kongtomorrow · Mar 19, 2002, 11:13 PM

Thanks a lot guys, I'll get the hang of this eventually.

And Rick I see you mentioned how to get better scaling. Sorry for making you repeat yourself.

Rickster · Mar 20, 2002, 03:07 AM

Sorry for making you repeat yourself.

That's okay, I don't mind. Oh, and did I mention you could get better image scaling by calling methods on NSGraphicsContext?