Opening = Losing?


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Picard

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May 27, 2004
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#1
Hi all,

I attended this talk where the speaker said that even by virtue of opening a digital picture with,say, Photoshop or any other editing software then closing it (w/o change of picture format, editing etc...just for a look), you WILL still lose picture quality.

Is that true?...frankly I don't believe but... :think:

Could someone enlighten me?
 

Azure

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Mar 16, 2003
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#2
Picard said:
Hi all,

I attended this talk where the speaker said that even by virtue of opening a digital picture with,say, Photoshop or any other editing software then closing it (w/o change of picture format, editing etc...just for a look), you WILL still lose picture quality.

Is that true?...frankly I don't believe but... :think:

Could someone enlighten me?
:rolleyes: :bigeyes: :bsmilie:
If you did not even save the image (if any changes done), how to affect it?
 

darkness

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Aug 11, 2002
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#3
You will only lose picture quality if you SAVE it, i.e., go through another layer of compression in jpg. The more times you save the more quality will be lost.

If you are just viewing it's ok.

Who's the speaker?? :eek:
 

zekai

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May 10, 2002
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#7
if the picture file is set to read only. he want to save also cannot.
So end of story, he is bull shitting.
 

Adiemus

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May 21, 2004
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#8
if the file is not saved... there is no loss in quality....
sigh... speakers should do their homework.... :think:
 

Zerstorer

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Jul 8, 2002
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#9
Probably a miscommunication.

If you do save when you close the file, it will affect, even if no change was made. He did state "editing software" so the process of saving is implied.
 

rueyloon

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#10
Picard said:
Hi all,
Is that true?...frankly I don't believe but... :think:

Could someone enlighten me?
this is totally not true, I would like to know who is the speaker :)
 

blurblock

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May 30, 2003
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#11
Picard said:
Hi all,

I attended this talk where the speaker said that even by virtue of opening a digital picture with,say, Photoshop or any other editing software then closing it (w/o change of picture format, editing etc...just for a look), you WILL still lose picture quality.

Is that true?...frankly I don't believe but... :think:

Could someone enlighten me?
The speaker is nuts, unless you save it everytime you open it (applicable to JPG only) it is not going to lose it's quality.

Loseless compression such as Compressed Tif, BMP or other formats do not lose it quality even if you save it a million time.
 

Picard

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May 27, 2004
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#12
Thanks guys, I think I get the message. I think I'd better not reveal his identity afterall we make mistakes and besides I was half asleep thru it...but what posted by 'Darkness' makes sense.

Thanks all!
 

Noir

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Apr 3, 2003
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#13
Picard said:
Hi all,

I attended this talk where the speaker said that even by virtue of opening a digital picture with,say, Photoshop or any other editing software then closing it (w/o change of picture format, editing etc...just for a look), you WILL still lose picture quality.

Is that true?...frankly I don't believe but... :think:

Could someone enlighten me?
The speaker is so mistaken. So all write once CD-R discs become re-writeable ones when u burn images onto them, open them and close them! ;p Sorry, can't help it. :D

Anyway, here's an interesting read on the block compression structure characteristic of JPEG which can be a useful read for people who edit JPEG files. For more, point to here ----> http://www.photofocus.com/zine7/jpeg.html

"For the truly curious, there are technically a few things you can do to JPEGs that will not degrade them. First, we need to go over some details about how JPEGs work. The human eye can see abrupt changes in tone better than in can subtle transitions. The JPEG process takes advantage of this by processing an image in blocks of either 16x16 pixels, 8x8 pixels, or occasionally even 8x16 pixels. Within each block a JPEG compression scheme attempts to smooth out the more subtle transitions without disturbing the edges that define objects in the image. Below, I show a close-up of a highly compressed JPEG image. Note the block structure. These blocks only start to become obvious when you've overdone things. But their influence is at work in every JPEG to varying degrees, when editing an image. As long as you don't disturb these blocks, no harm comes to the image. But it's pretty hard to pull that off.

Certain specialized editing programs can take advantage of this block structure to perform tricks with JPEG images. They do so without expanding and recompressing them. Rotations of 90 or 180 degrees in either direction can be done relatively easily. It is also possible to crop an image (so long as it is done on block boundaries) beginning in the upper left hand corner. Remember that in most programs, including PhotoShop, you can't do this. Windows XP now has a graphic viewer that will let you rotate images as well, but you should resist the temptation. Ditto with Apple's iPhoto for Mac OS. As with PhotoShop, both of these actually decompress the image, rotate it, then resave with the accompanying loss of quality that comes with it. ACDSee is the most popular program that actually offers lossless JPEG rotation. A free online service that can do lossless JPEG rotation is available as well, courtesy of Pegasus Imaging.

You can also take advantage of the block structure when editing your image in any program, if you resave it with exactly the same settings that were used originally. If you don't use exactly the same settings, you'll lose more information each time you save. If you don't change any settings, any blocks that were unmodified should compress again without any significant degradation. Quality levels and compression settings are not standardized across programs either. So you are unlikely to be able to avoid degradation if you edit a JPEG with more than one program, no matter how hard you try to use the same settings. Keep in mind that any global changes, such as brightness, contrast, tone adjustment, white balance or sharpening, will affect all blocks and result in quality loss no matter what program you use. Your best option is to stick with PhotoShop's native PSD or other non-compressed format for all your editing."
 

snowspeeder

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Feb 16, 2004
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#14
Well let me think....if each time i save an image and it loses some quality. Then does it mean that after savings a certain XX number of times, the image will deteriorate beyond visual recognition? :bigeyes:
 

Spyer2

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Mar 20, 2004
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#15
snowspeeder said:
Well let me think....if each time i save an image and it loses some quality. Then does it mean that after savings a certain XX number of times, the image will deteriorate beyond visual recognition? :bigeyes:
:bsmilie: you can try it..
 

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