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Exporting to .jpg

Dec 8, 2013, 16:58 (This post was last modified: Dec 8, 2013 18:22 by russbrett.)
Post: #1
Exporting to .jpg
My artist uses Adobe Photoshop CS4 and saves the images as a .jpg (as required by our printer).

I want to be able to make slight changes to his art (text only) without having to bother him.

I'm concerned about maintaining print level quality of the .jpg.

On the current page I'm working on, HIS .jpg is 4.81 mb

When I open it in Gimp, make my changes, and then export it as a .jpg, it is only 1.08 mb

I'm concerned that there is a resolution loss, and the Gimp generated .jpg will not be print quality.

It doesn't appear that any other settings are changing (pixels or dpi), but I really have no idea how to use this software.

Any help is appreciated. Thanks in advance.

Russell Brettholtz
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Dec 8, 2013, 18:28 (This post was last modified: Dec 8, 2013 18:28 by russbrett.)
Post: #2
RE: Exporting to .gif
(Dec 8, 2013 17:47)ofnuts Wrote:  There are two things that influence quality, the "quality" setting and the "chroma subsampling" in the advanced options. But there is a lot of difference in size for rather small variations of the quality setting in the 85-100 range, and comics that have a limited number of colors and large areas of uniform colors may have a specific behavior when compressed.

Thank you for the response.

But I have no idea what you just said.

Do you think the Gimp generated .jpg at 1.08 mb is still print level quality?

Quote:PS: why is the topic title mentioning .GIF?

Because I'm an idiot.

I fixed it.

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Dec 8, 2013, 23:51
Post: #3
RE: Exporting to .jpg
2 pages of resources to better understand subsampling .jpeg in Gimp
Jpeg compression/Examples
http://docs.gimp.org/2.6/en/gimp-tutoria...-jpeg.html

Scroll down to "1.2.2. Export Image as JPEG"
(ctrl + F, type the quoted to jump to it)
http://docs.gimp.org/en/gimp-images-out....ort-dialog

Note the photo, Subsampling part
All the options are explained if you scroll down further.

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Dec 9, 2013, 00:46
Post: #4
RE: Exporting to .jpg
The image is 2063 x 3131.

I'm not sure how determine quality (or what that term "technically" refers to).

Seriously, I'm an idiot when it comes to graphic design.

But I appreciate the help.

Russell Brettholtz
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Dec 9, 2013, 02:17
Post: #5
RE: Exporting to .jpg
(Dec 9, 2013 01:20)ofnuts Wrote:  JPEG is a "lossy" format. The compressed image doesn't hold as much detail as the original. In photography (and in photography only, this is the "P" in JPEG) loss of detail isn't visible until the file size has dramatically reduced, so JPEG is a good format. For other applications, loss of detail shows very quickly (around sharp edges, typically: text, logos, and other CGI such as digital comics) so you have to keep a big file size.

The "Quality" is how you set the compromise between loss of detail and file size (at 100% you don't lose any detail).

Thank you. That helped. When I exported at 100 Quality the file was 3.36 mb (clearly better).

Does Gimp only use the RGB color palette. My printer uses CMYK and that's what the files were originally drawn in (or do you think it won't ostensibly matter? - the changes I'm making are only for a 4-page ashcan preview).

Russell Brettholtz
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Dec 9, 2013, 10:19
Post: #6
RE: Exporting to .jpg
Quote:...I exported at 100 Quality the file was 3.36 mb (clearly better).
Does Gimp only use the RGB color palette. My printer uses CMYK and that's what the files were originally drawn in (or do you think it won't ostensibly matter? - the changes I'm making are only for a 4-page ashcan preview).

You are delving into the dark arts here Wink There is a difference in file size between RGB and CMYK.

Just for info: I faked-up a 2063 x 3131 pix image. saved it with Gimp, obviously RGB, used the 90 quality setting.
Then using PS7 opened and resaved as a CMYK image. Twice, once with an embedded cmyk profile, and again without. PS uses a different quality scale 1 - 12 so I used 10.

File size in MB
RGB 1.917
CMYK no profile 3.37
CMYK embedded ISO coated profile 5.00

So the original file size quoted 4.81 MB could include a a sizable chunk of colour information, anything from .25 MB (FOGRA27.icc) to 1.5 MB (ISOcoated.icc)

Ask your artist what he uses, if anything.

Gimp does not edit in CMYK, but it can export as a jpeg using a plugin, separate+
my demo here: http://www.youtube.com/watch?v=2rby7r771D4&hd=1
but not the best way, best way is use CMYK from start to finish.

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Dec 10, 2013, 00:20
Post: #7
RE: Exporting to .jpg
Thanks to all for your help.

I think I'm a bit out of my depth though.

I think I'll just run a test print off the best quality I can create. It's just an ashcan, and it's only the cover, so hopefully the quality will be good enough.

If not... I'll be back.

Russell Brettholtz
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Dec 15, 2013, 21:30
Post: #8
RE: Exporting to .jpg
Thank you, everyone!

With the help you all provided I was able to make the changes I need. I printed a test copy on Friday and it came out perfect.

Russell Brettholtz
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