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Thread: A question for the digital experts here

  1. #1

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    A question for the digital experts here

    Hi guys, here's a question about the quality of JPEG's, for those who really understand this stuff. I have several very large image files that I am having printed at Duggal. To save the image as a TIFF requires using a DVD because they're 800MB, larger than what a CD will hold. But if I save the images as 12-quality JPEG's, they are only 140 MB, which can easily be stored on a CD.

    So out of curiosity, I tried saving the file both ways, and then opened both files and compared them at 1600%. I could see no visible difference, even in the areas of highest detail and tonal smoothness. The JPEG had every bit of detail and color as the TIFF file did. So the question is, is there any real difference between saving files as uncompressed TIFF's (which takes tons of space), and using the highest-quality JPEG option? If 12-quality JPEG's are just as good, I could save the most humgous amount of hard drive space here.

    ~cj

  2. #2

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    Re: A question for the digital experts here

    Hi Chris...

    While I've never compared as you did, I always send my digital files as 12-quality JPEGs and I've never seen any discrepancies/differences at all in the finished work.

    However, I always archive my master files as PSD docs, with all layers intact.

  3. #3
    Scott Rosenberg's Avatar
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    Re: A question for the digital experts here

    chris, i'm not an expert by any means, but when comparing the images on a screen, i would imagine that the limitations of the display would outweigh the differences between the format the file is saved under. have you tried making prints to compare? someone here might have already done this, but i suspect that would be a better way of comparing quality sacrificed by jpeg compression.

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    Re: A question for the digital experts here

    Quote Originally Posted by Scott Rosenberg View Post
    i would imagine that the limitations of the display would outweigh the differences between the format the file is saved under
    Hmmm...viewing at 1600%, if there are no differences in color or contrast, I'd say you'll never see it in a print of any practical enlargement.

  5. #5
    Ted Harris's Avatar
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    Re: A question for the digital experts here

    Scott is right about the limitation s of some screens. Beyond that .... TIFF files are lossless meaning that you can open them again and again and never loose any of the information. JPEG's OTOH are losey meaning that every time you spen and then resave a JPEG you lose a tiny bit of information, after some number of iterations of opening and closing (resaving) there will be some image degradation. Much of the degradation n a JPEG is due to the fact that the info is always stored in a compressed format ... even if you save at the highest value. TIFF's OTOH are saved uncompressed unless you specifically request they be compressed and then you have compression choices that will dramatically reduce info loss, choices that are not available for JPEG's.

    BTW, if you are concerned about how you store the data for printing why not ask if they have an option for you to use an FTP client to upload your files?
    Last edited by Ted Harris; 13-Nov-2006 at 13:50.

  6. #6

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    Re: A question for the digital experts here

    The biggest difference between yopur master image and a 1st generation 12-quality jpg would be if your master file is 16 bit. jpg's are by default 8 bit files. If your master file is also 8 bit then ther will not be any tone shifts in the jpg.

    The amount of lossy compression in a 12-quality jpg is quite small so I doubt you would be able to see any compression artificats in your print.

  7. #7

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    Re: A question for the digital experts here

    Quote Originally Posted by Greg Miller View Post
    The biggest difference between yopur master image and a 1st generation 12-quality jpg would be if your master file is 16 bit. jpg's are by default 8 bit files. If your master file is also 8 bit then ther will not be any tone shifts in the jpg.

    The amount of lossy compression in a 12-quality jpg is quite small so I doubt you would be able to see any compression artificats in your print.


    I need to amend my comment on tonal differences. Jpgs also need to be in srgb color space. So if you are converting from a color space with a wider gamut (such as Adobe RGB 1998 or ProPhoto RGB) then you may see a change in tones.

    External hard drives are a good alternative here. You can pruchase a very small external hard drive at a pretty cheap $ anout. You could copy your tiff file to the external hgard drive and then ship that to Duggal.

  8. #8

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    Re: A question for the digital experts here

    You should also try using LZW compression of your TIFF files. LZW is a lossless compression. Since you are starting at 800mb, this could very well get you down to a file size small enough to fit on a CD. And with no image degradation worries.

  9. #9

    Re: A question for the digital experts here

    Quote Originally Posted by chris jordan View Post
    ...is there any real difference between saving files as uncompressed TIFF's (which takes tons of space), and using the highest-quality JPEG option? ...

    ~cj
    Chris,

    Have you tried using compressed TIFF format? The LHZ or ZIP compression in TIFF is a lossless compression method. It doesn't look at the image, it looks are the strings of bits and does compression where it finds data that can be compressed. That may reduce your size to CD levels.

    As Ted says, JPEG is a 'lossy' compression method, but I wouldn't hesitate to use the highest quality setting for a file that I need to send out. Just avoid ever having to open and re-save that file because the compression artifacts will increase when this is done. Generally, I'll make a JPG for that purpose, and then dump it so it doesn't get in the editing pipeline again. I'll go back to the TIFF or PS file (with layers) for more editing.


    ---Michael

  10. #10

    Re: A question for the digital experts here

    Greg,

    JPG is sRGB only if you don't specifically assign a profile. It can have any normal profile embedded within it so there isn't a loss of color information using JPG.


    ---Michael

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