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Windows 7: how much quality is lost when i save in jpg rather than png format

08 Feb 2012   #21
Duzzy

Windows 7 Ultimate x64
 
 

Quote:
An interesting experiment is to take an image, and save to a new name, and compare the quality of the images, (setting the compression to high will speed up the process).
To add to this, more compression equals lower quality and smaller files, less compression equals better quality and larger files.

@Barman
Quote:
set the snipping tool JPEG settings to highest to retain as much detail as possible.
Can you do that with the snipping tool, how?


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08 Feb 2012   #22
jturk

windows 7
 
 

Quote   Quote: Originally Posted by Barman
Saving a file from the snipping tool to JPEG, which you are not going to edit is OK as the JPEG compression process is only performed once, thogh it will degrade to some extent, set the snipping tool JPEG settings to highest to retain as much detail as possible.
it sounds like you have already answered this but i want to be clear. i dont plan to edit any images once ive saved them. that being said, how much will saving in a jpg rather than png "degrade" the image?

also, how do you set the snipping tool jpg settings to retain as much detail as possible?

thank you.
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08 Feb 2012   #23
Influx

Win7 Ultimate x64 SP1 / WCP x64 / Ubuntu 11 x64
 
 

Quote   Quote: Originally Posted by Barman58 View Post
Quote   Quote: Originally Posted by manhunter2826 View Post
Quote:
, every edit and save as a JPEG file will have a detrimental effect on image quality.
wow, thanks barman, that i never knew. any reason why this happens -- short explanation ? lol
a Jpeg image discards information that is deemed to be un-necessary for the human eye to "see the image", this reduces the size, but also removes subtle detail. As this process is repeated every time a file is saved, the image quality is reduced each time.

An interesting experiment is to take an image, and save to a new name, and compare the quality of the images, (setting the compression to high will speed up the process).

When the jpeg system was developed the web was young and image quality was low so this loss was not really an issue, but today with high bandwidth, and HD screens the compression can be noticeable with "artefacts", (stray pixels and blocky images).

If you wish to retain quality for the web, the PNG image which has a better lossless compression is the way to go.

I do keep Jpeg images from my own camera but the system I use keeps a master copy, and a list of changes and "publishes" a copy for upload as required. A lot of my original images are stored as digital negatives (Raw), format which creates huge files but can be edited continuously without detail loss.

Hope that's short & simple enough, unfortunately image compression is a complex subject
I agree. Interesting and Great Information. JPEG is still widely used on animations, gfxs though.
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08 Feb 2012   #24
ignatzatsonic

Microsoft Community Contributor Award Recipient

Windows 7 Home Premium SP1, 64-bit
 
 

Quote   Quote: Originally Posted by jturk View Post

it sounds like you have already answered this but i want to be clear. i dont plan to edit any images once ive saved them. that being said, how much will saving in a jpg rather than png "degrade" the image?
Take a few jpegs and play with them as a test.

Do some minor editing and save as jpeg. Reopen this edited jpeg, do more minor editing, and resave. Etc.

Go back to the original, do the same minor editing you did on the jpeg, and save as png. Reopen the edited png, do more minor editing like you did on the jpeg, and resave as png, Etc.

If you re-edit the jpeg a number of cycles, the defects will become visible, particularly under a zoom. Aging eyes or a small low resolution monitor are more forgiving.

It plays hell with wallpaper. If you are fussy about wallpaper and do a lot of cropping and editing to get them just right, make all saves in a lossless format--png, tiff, bmp.
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08 Feb 2012   #25
Qdos

 

In photo editing programs you can choose the amount of compression on JPG images.

By default it's often set at 30%, you can adjust it to nil however.

That way editing is effectively lossless
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08 Feb 2012   #26
Barman58

Windows 10 Pro x64 x2 Windows 10 Enterprise x64, Ubuntu
 
 

Quote   Quote: Originally Posted by Duzzy View Post
Quote:
An interesting experiment is to take an image, and save to a new name, and compare the quality of the images, (setting the compression to high will speed up the process).
To add to this, more compression equals lower quality and smaller files, less compression equals better quality and larger files.

@Barman
Quote:
set the snipping tool JPEG settings to highest to retain as much detail as possible.
Can you do that with the snipping tool, how?
Sorry my bad , this is not an option in the snipping tool, though I can remember setting this so must be available in alternative applications
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08 Feb 2012   #27
Barman58

Windows 10 Pro x64 x2 Windows 10 Enterprise x64, Ubuntu
 
 

Quote   Quote: Originally Posted by jturk View Post
Quote   Quote: Originally Posted by Barman
Saving a file from the snipping tool to JPEG, which you are not going to edit is OK as the JPEG compression process is only performed once, thogh it will degrade to some extent, set the snipping tool JPEG settings to highest to retain as much detail as possible.
it sounds like you have already answered this but i want to be clear. i dont plan to edit any images once ive saved them. that being said, how much will saving in a jpg rather than png "degrade" the image?

also, how do you set the snipping tool jpg settings to retain as much detail as possible?

thank you.
Sorry for confusion, looks like snipping tool is fixed, One way would be to save as PNG and then use an editor to create any JPGs as required.

As for losses an example file I've just checked is 4912 x 3264 pixels and the digital negative file is 16.15MB in size, which is just over 16MB for the image (16032768 bytes), plus a little for overheads. The jpeg is only 8.5MB so almost half of the original data is missing, though of course the actual method used for compression would mean that the JPG version is not simply half as detailed but is considerably degraded. this export was done at 100 which is for maximum detail a setting of 50 gives a file just over 1MB but with visible degredation.

A useful comparison with some example images is at http://www.wfu.edu/~matthews/misc/gr...s/formats.html
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08 Feb 2012   #28
DeaconFrost

Windows 7 Ultimate x64 SP1
 
 

You can't add quality to a photo, so when saving images from the web, why not just leave them in the format they are already in?
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08 Feb 2012   #29
FliGi7

XP / Win7 x64 Pro
 
 

Quote   Quote: Originally Posted by jturk View Post
i want to save in png rather than jpg so that i dont lose any of the quality.

also, how much of the quality is lost by saving in jpg instead of png?

im saving pics directly from websites btw.
Why exactly are you trying to preserve the utmost quality on the downloaded images?

As an aside, if you're trying to save jpg's from the web as png's, you might want to stop and think if/how that makes sense to save an image that's already been compressed and image quality lost into a lossless format. It may make sense for you since we have no clue the reasoning behind this, but that's something to think about.
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08 Feb 2012   #30
gigagiggles

Windows 7 Home Premium x64
 
 

"i want to save in png rather than jpg so that i dont lose any of the quality.
im saving pics directly from websites btw."

It can't be done. You're after fool's gold.

The websites' authors have already done the compression prior to placing the images onto the webpages before uploading. They took into consideration the bandwidth, traffic and browsing experience to have some loss in quality of images. If the authors decided on png's, you're in luck. If it's jpg's, then that is the format of the pictures you're saving.
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