Re: Image scaling

FROM : John Stiles
DATE : Sat Jan 05 00:51:02 2008

I'd suggest that if you are trying to demonstrate an image's sharpness,
a lossy format like JPG is not the format to use :)

FWIW it's entirely possible that Flickr is explicitly running a
sharpening filter on the image before scaling it down. I am not 100%
sure but I am fairly positive that Google's photo service (Picasa) does
this when you scale down images from within its iPhoto plugin.


Adam Knight wrote:
> On Jan 4, 2008, at 4:25 PM, Adam Knight wrote:
>

>> I tried this using CIImage and a CILanczosScaleTransform filter then
>> using NSBitmapImageRep's initWithCIImage method.  This worked very
>> well and made a great image, but it looks like Apple's
>> initWithCIImage code leaks a whole copy of the image outside of my
>> reach.  I'm working with too many images for this to be good.  Also,
>> this method drops the file metadata entirely (EXIF, etc.) and doesn't
>> appear to give me the chance to add it back in.

>
> I take this back -- even this method produces slightly blurry scaled
> images.  Is there anything in the system that can make a sharp, proper
> scaled image?
>
> Examples:
>    http://www.bssware.com/~ahknight/good_scale.jpg (Image uploaded to
> Flickr in full size, the resulting image at 500px wide)
>    http://www.bssware.com/~ahknight/bad_scale.jpg (Scaled using
> either CG or CI to 500 pixels wide)
>
>
> Adam Knight
> Co-Founder; CTO
> Barton Springs Software
>
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