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Input/Output/Workflow Scanning, printing, color management, and discussing best practices for control and repeatability

make me understand re lossy

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  #1  
Old 10-16-2001, 05:13 PM
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kathleen kathleen is offline
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make me understand re lossy

please.

if you have a psd open, and you change it to a jpeg, and you change it right back to a psd without ever having closed it as a jpg, do you lose anything?

i am thinking re storage. recently lost my hard drive, had my most critical stuff on zip disks, which @ the moment is my only storage option. i had run out of disks, but much of what i had saved i had saved as psds, would prob. have had room for everything if i'd saved them as jpgs. if you change a psd to a jpg, save it as a jpg, open it and convert it back to a psd, how much do you lose?

i hope this question makes sense. and if it matters for the answer, i have a mac.
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Old 10-16-2001, 06:11 PM
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Ed_L Ed_L is offline
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Kathleen,

I'm not the authority on this, but it is my understanding that you only lose quality when the file is saved. There's a good possibility that I could be wrong. You said "if you change a psd to a jpg, save it as a jpg, open it and convert it back to a psd, how much do you lose? " If you didn't close the image, you wouldn't need to open it again. If you *did* close it, you have lost something in quality. At least that's the way my thinking goes. If I'm wrong, somebody please correct me.

Ed
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Old 10-16-2001, 08:28 PM
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DJ Dubovsky DJ Dubovsky is offline
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Kathleen
JPGs tend to loose some file info which may not be visible to the naked eye but remeber if you save from a psd to a jpg you will loose any layers you have and any saved selections in the channels pallette. The better file to save in would be a tif so you don't suffer data loss but even that will delete your layers and alpha channels and is still a larger file size than you may be looking for.
Generally when you save (not save as) and change the file extension you loose the data whether you close it or not. If you save as, and change the file extension, you will have two files saved. Before you go saving to a different format, make sure you won't want to go back to it in it's layered form before you do. If it's a space problem, save the files on CD (verify the files saved correctly) then delete the ones on hard drive to give more space. I always save a psd file and make a jpg or tif as a finished print file. Hope that helps.
DJ
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Old 10-16-2001, 08:36 PM
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Why couldn't you just save the file in it's original format, then flatten and resize (if necessary) and save it as JPG? That way you should have the original file saved without a loss, and the JPG file would also be available.

Ed
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Old 10-16-2001, 09:12 PM
Vikki Vikki is offline
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From everything I've read, saving as jpg will degrade your file.
If you're concerned about saving hard disk space, why not keep your files in an online album.

I had so many photos (I have a digital camera), I had to buy a cd writer! Best investment I ever made too. Maybe something to purchase down the road.
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Old 10-16-2001, 09:26 PM
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what i glean from all of the above is i prob could have saved much of what i had as jpgs and done ok; i had a lot of originals that i had never touched so would not have involved layer or channel loss.

alas, no cd burner. yet. i'd ask for suggestions, but don't know if they're mac/pc specific.

thanks guys.

oh and vikki, you popped in while i was writing this - that is a good idea about the online storage, has occurred to me since the untimely demise of hd#1. but you couldn't store psds like that, could you?
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Old 10-16-2001, 09:35 PM
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I read what you said and then forgot you said you only had a zip drive for storage. Those photos can be pretty big and I suppose a zip isn't convient storage. The CD writers arn't that expensive these days ($40 to $100) and the benefits you get from them will out weigh any cost. Especially when you have a hard drive go on you and you loose files.
DJ
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Old 10-16-2001, 10:00 PM
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Kathleen,

I just realized that I might have misunderstood what you were asking. If you were asking how much you lose *in a PSD file* after saving it to JPG then converting it back, I understood you correctly. If you were asking how much you lose by saving to JPG (period), that's a different story. I belong to a scanning mail list, and they are having a discussion about JPG and losses. Some of the brightest people on the list feel that if you saved a JPG at the highest level (12), it would be lossless. At any lower settings, the loss would become more with each decreasing number. In other words, the more compression, the more loss. Each time the file is saved, more loss occurs. So, if you were saving JPG's at the lowest compression, and not opening and saving it several times, there would probably be little loss, if any. At least that's my impression. Of course it would need to be a flattened file. Hope this helps.

Ed
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Old 10-16-2001, 10:13 PM
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yes ed, it helps a lot. answered my unasked question about what are all those different levels of jpeg about. and you did understand me right.

never tried to save straight to jpg; even if you did it at the highest level it would still be smaller than a psd or tif, wouldn't it? that's something i guess i can prove for myself easy enough, will check it out. intelesting.
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Old 10-16-2001, 10:20 PM
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You probably already found out, but yes, jpg at it's highest setting still makes for a smaller file size then a tif or a psd.
DJ
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