At 11:25 AM +0200 18/4/11, Žorvaršur Davķšsson wrote: >On 07.04.2011, at 03:42, Geoffrey Heard wrote: > >> It is desirable to avoid editing in iPhoto as >>it applies rather savage lossy compression each >>time you edit and save and you have no control >>over it, so it is best to edit in an external >>program and save without loss back into iPhoto.) > >This may be the right time to ask about >something I always wanted to know about but was >afraid to ask. > >Every time I open a jpg file in Finder with a >double-click it is decompressed when it opens. >When I close the file it is compressed again. If >I understand this process correctly then >repeatedly compressing and decompressing a jpg >file will cause it to progressively lose >quality. Therefore I'm beginning to ask myself >whether it is not best to convert ALL valuable >Photos (such as family photos) to PNG (which is >a lossless format) with GraphicConverter >*before* I import them into iPhoto. > >Most of my photos have been downloaded from the >Internet and they are all in jpg format. Should >I also convert them to PNG? Or do I have to open >and close a jpg file several thousand times >before I begin to notice any quality loss? > >Pictures are really not my strength, therefore I >would be grateful for any recommendation >regarding this. hello Žorvaršur When you double click and open the JPEG to look at it, it doesn't get compressed again when you close it, it stays the same. JPEG compression is not like packaging something in a bag and squashing it, it is making a permanent change to the contents so they are smaller. Basically, differences are removed. In an uncompressed file, you might have a bunch of 64 pixels (number simply pulled out of the air for illustration) that are all a little different and therefore all are described separately so the file is big; after JPEG compression, if the differences are small within the limits of compression applied, then all those 64 pixels will be considered the same, so they will all have the same description, and that one description will simply be applied to all 64 pixels. But where you had a fine gradation beforehand, now you have a single tone. So while the file has been made much smaller, it has lost detail and that lost is irrevocable.. So in the end the file is smaller because there is less information in it! It's not like packaging up a bunch of code in a .zip or .bin file which expands when you open it. With JPEG compression of graphics, you actually have discarded information which cannot be retrieved. This happens only when you save the file, with compression applied. Not when you simply open it to look at it. However, if you open it then save it again with more compression applied, you lose further detail because the existing file, whether it has been compressed or not, is regarded as the 100% original, so a 70% quality level saving is 70% compared with the file's 100%, even though that file is already at 70% quality compared with the original. So it groups out 64 pixels with other neighboring pixels, which weren't grouped with it in the first saving and the area of a single tone is increased again ... PNG format? That's a web format. It is pretty stripped out but superior to JPEG in retaining transparency (JPEG makes transparent areas white). I'm not sure how iPhoto handles PNG. I would store important photos in TIFF format. It's big but it works. There is non-lossy compression available. The way around all this is to specify in the iPhoto prefs that you will use an external editor. I am using PhotoLine, you will prefer Graphic Converter, Erick (and one of two others around the world) use Photoshop. Once you have selected that in the prefs, then when you double click on a thumbnail in iPhoto, it launches the external converter with the photo open ready for editing. When you save back, it saves in whatever format you specify in the external program. I'm currently saving back in TIFF or 100% JPEG (no compression in PhotoLine). iPhoto Buddy came in before iPhoto allowed multiple libraries. it remains a handy way to manage multiple libraries; handy for me at any rate. And since it is donation-ware, it doesn't cost much. Cheers, geoff Geoffrey Heard Business & Environment Writer, Editor, Publisher The Worsley Press Buy "Type & Layout: Are you communicating or just making pretty shapes?" -- the world's ONLY scientifically based guide to type and layout, and receive a free 140 page guide to advertising for small business: "How to make great ads for (small) business: 99 real world advertising ideas to kickstart *your* business today". Amazon or http://www.worsleypress.com