can a Cocoa app scale jpeg images as nicely as Preview does?

Folks --

When I load a jpeg image into my app and shrink it, certain images look
pretty awful. When I open the same image in Preview and Zoom a
bunch of times, it briefly looks awful, but then it sharpens up and
looks great.

For example, try grabbing
<and
doing Zoom six times, scaling it down 8x in each dimension. You can
almost read the text.

When I scale that image by the same amount in a simple Cocoa app (by
resizing the NSImage or by making the NSImageView the right size), it
comes out pretty ugly


I’m sure there are techniques and libraries out there to do this, but I
thought NSImage would do a good job right out of the box

Thanks,

-- Mike

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You can get better scaling via -[NSGraphicsContext
].
Ali



Begin forwarded message:

From: Mike Morton <mike.morton (AT) sonos (DOT) com>
Date: 6, 2005 9:34:33 AM PDT
To: Cocoa-Dev <cocoa-dev (AT) lists (DOT) apple.com>
Subject: can a Cocoa app scale jpeg images as nicely as Preview does?
>
Folks --
>
When I load a jpeg image into my app and shrink it, certain images
look pretty awful. When I open the same image in Preview and Zoom
a bunch of times, it briefly looks awful, but then it sharpens
up and looks great.
>
For example, try grabbing <
B000006TRV.01._SCLZZZZZZZ_.jpgand doing Zoom six times,
scaling it down 8x in each dimension. You can almost read the text.
>
When I scale that image by the same amount in a simple Cocoa app
(by resizing the NSImage or by making the NSImageView the right
size), it comes out pretty ugly
>
>
I’m sure there are techniques and libraries out there to do this,
but I thought NSImage would do a good job right out of the box
>
Thanks,
>
-- Mike

Do not post admin requests to the list. They will be ignored.
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Ali et alia --

This worked great.

Googling for setImageInterpolation:, I found
<>. the techniques
there, I found that I had to use drawInRect: -- compositing didn’t
work for me.

I wound up doing:

NSImage *result = [[[NSImage alloc] initWithSize: newSize]
autorelease];
[result lockFocus];
[[NSGraphicsContext currentContext] setImageInterpolation:
quality];
[self drawInRect: NSMakeRect (0, 0, newSize.width,
newSize.height)
fromRect: NSMakeRect (0, 0, currentSize.width,
currentSize.height)
operation: NSCompositeCopy
fraction: 1.0];
[result unlockFocus];

Thanks!

-- Mike


6, 2005, at 4:02 PM, Ali wrote:

You can get better scaling via -[NSGraphicsContext
].
Ali
>
>
>
Begin forwarded message:
>
>From: Mike Morton <mike.morton (AT) sonos (DOT) com>
>Date: 6, 2005 9:34:33 AM PDT
>To: Cocoa-Dev <cocoa-dev (AT) lists (DOT) apple.com>
>Subject: can a Cocoa app scale jpeg images as nicely as Preview does?
>>
>Folks --
>>
>When I load a jpeg image into my app and shrink it, certain images
>look pretty awful. When I open the same image in Preview and Zoom
>a bunch of times, it briefly looks awful, but then it sharpens up and
>looks great.
>>
>For example, try grabbing
><
>and doing Zoom six times, scaling it down 8x in each dimension.
>You can almost read the text.
>>
>When I scale that image by the same amount in a simple Cocoa app (by
>resizing the NSImage or by making the NSImageView the right size), it
>comes out pretty ugly
>>
>>
>I’m sure there are techniques and libraries out there to do this, but
>I thought NSImage would do a good job right out of the box
>>
>Thanks,
>>
>-- Mike
>

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