Re: how to cache images
Re: how to cache images
- Subject: Re: how to cache images
- From: Ken Thomases <email@hidden>
- Date: Sat, 08 Jun 2013 14:24:09 -0500
On Jun 8, 2013, at 2:05 PM, Jens Alfke wrote:
> On Jun 8, 2013, at 8:01 AM, Ken Thomases <email@hidden> wrote:
>
>> Alternatively, you could force the image to load and then use +[NSBitmapImageRep representationOfImageRepsInArray:usingType:properties:] to create an NSData from the image's representations and save that to file.
>
> Not a good idea. If you do this with images that were originally JPEG, you’ll degrade the image quality if you save it out as JPEG again, since it’ll have to run the pixels through the lossy encoder again. Or if you save it in a different format the file size will go up a lot.
I haven't done the experiment, but I don't believe this is necessarily true. NSBitmapImageRep is documented (in the Snow Leopard release notes) as keeping the original image data and not re-encoding or exploding file sizes on being saved.
"You should see less encoding and decoding of bitmap data as CGImages. If you initialize a NSImage from a JPEG file, then draw it in a PDF, you should get a PDF of the same file size as the original JPEG. In Leopard you'd see a PDF the size of the decompressed image."
Search for "NSBitmapImageRep: CoreGraphics impedance matching and performance notes" on this page:
https://developer.apple.com/library/mac/releasenotes/Cocoa/AppKitOlderNotes.html#X10_6Notes
Regards,
Ken
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