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Thread: restoring a jpeg file

  1. #1
    Wessex Wildlife's Avatar
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    restoring a jpeg file

    Hello Clever People, I need help. I have some images that were taken as jpeg files with my trusty Canon 20D. They were taken at a time before I learned much about post-processing. I want to apply some simple adjustments to the images. I can do a certain amount to a jpeg, but is there something I can do to the images (such as convert it to a smart object) that will provide more options? I am using Photoshop CS4. I want to include these images, which are all about 1MB - 3MB in size, in a print exhibition; reproduced at about A4 size.

    All tips welcome. Thank you,

    David.

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    Re: restoring a jpeg file

    You could get your editing programme to increase the pixel count ... don't use CS but it was simply a matter of resizing after stipulating the dpi. It is called interpolation by some, resampling by others and when I used a 3.3Mp camera I did it all the time when going for A3 prints.
    It will not make the images better and detail will become slightly or considerably blurred but at least the pixel peepers will not see the pixels
    Itt can work well if you do not push the process too much, how much is too much depends on the subject matter ... a detailed landscape less than a big bold portrait etc.

    Some will argue for less but 300dpi is usually quoted and was/is the printing industry standard for quality printing, though I remember my printer [photo lab] telling me they used 600dpi. Another wrinkle suggested years ago was that the dpi should, when divided into the printing machines resolution ability, result in a whole number ... on that basis some used 360dpi with a highly reguarded printer of the time.
    Bearing in mind that dpi=ppi=dpi=ppi
    Last edited by jcuknz; 10th June 2013 at 09:36 PM.

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    Re: restoring a jpeg file

    Hello David
    Do you have the original, out-of-camera jpegs? If so, make copies, convert the copies to .tif files (or save the copies as .tif files), and put the originals somewhere safe. You should be able to do anything, and everything that Photoshop allows, with .tif files including resizing and resampling as well as any image adjustments. Files that are 1 - 3Mb should be able to be resized for A4 prints satisfactorily, all other things being equal.
    On the other hand, if you have already played with the .jpegs it is probable that your quality options are now limited because some information may have been lost in the adjustment and saving processes - that's the nature of .jpeg files.

    Tim

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    dje's Avatar
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    Re: restoring a jpeg file

    Hi David

    I have a slightly different view to Tim in that I believe you should be able to do all the editing you want on the jpeg files. I can't see how converting them to another format will open up different editing possibilities. But when you have done your editing, use Save As (not Save) to make sure you don't over-write the original jpegs. The format you Save As is up to you but my suggestion would be PSD files which can be edited later if necessary and can be used to export any format and size you like at any time.

    You can use Smart Objects in PS if you like but that doesn't really give extra editing possibilities, just the ability to open up the PSD at a later date and change some of the adjustments. A simpler way to do this for many adjustments is to use adjustment layers however there are some adjustments such as filters and Shadows/Highlights that you need to use Smart Objects for if you want to re-adjust later.

    Judging by the size of the jpeg files, they were probably saved with a fairly high quality jpeg setting and so you probably haven't lost too much with the jpeg compression.

    Dave

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    Re: restoring a jpeg file

    Keep in mind that editing programs do not use jpeg internally, but use their own data formats to work with (and those don't need to have any relation with file formats).
    That means that any image format will be translated to the internal format on loading of the file. So there's no special trick to convert a jpeg into a better editing object.
    What is important is to store the intermediate results in a lossless format (psd when using photoshop and layers, tiff, or png when you have only one layer); don't use jpeg
    for intermediate results. And of course always keep the original files intact and in a safe place.

    300 ppi is indeed a printing standard (and close to the 'normal' resolution of human vision) for material to be watched from ~30 cm. For a print exhibition,
    viewing distance will probably be larger, so print resolution can be lower. Also, the material and finish of the print is important: a print on glossy paper with very
    little texture shows more details than the same image on mat, textured paper or canvas.

    So ideally, an A4 print should require about 6 MP for handheld on glossy paper; hang it on a wall, and 3 MP would probably work.

    @David: I just notice: you cite your image size in MB, that's an almost useless unit for jpgs, as they are more or less heavily compressed, depending on quality
    setting and on image content. And don't bother about the DPI setting in your editing program, if you need a specific resolution, calculate the number of pixels
    you need and adjust that if needed (i.e. not very often)

    Finally: DPI != PPI: printers can use an array of dots for each image pixel.

    Remco

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    Wessex Wildlife's Avatar
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    Re: restoring a jpeg file

    Thank you! I knew there were lots of clever folk out there. Having that range of advice and solutions is great as I will apply slightly different methods depending on the image content and reproductive size.

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    Re: restoring a jpeg file

    David,
    I'm not sure if CS4 will do this as i missed that one...

    Open all images in ACR, and save as DNG. This has two advantages - it gives you a lossless copy of the originals, it takes less space than Tiff, there's a lot you can do in ACR, and you can always change your mind; editing in ACR doesn't change the image as such, but applies edits, and appends these to the original file. Well, the DNG

    I did say two advantages, didn't I? Well, in this case more is better...

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    Re: restoring a jpeg file

    Hi again David
    there's a lot of debate floating about re PSD, TIFF, DNG. I'm not taking sides. The key thing we all agree on is, don't do intermediate saves on a file you're working on, in JPEG format. It's lossy, and consequently can be lousy!
    RE printing standards: check with your printer. If they're using Canon or HP gear or similar, 300 dpi is the dot pitch images will eventually need to be sized to for exhibition viewing. If they're using Epsons 360 dpi is the native dot pitch. (if you're fascinated by why this difference comes about, (and few people are), see http://fromcameratoprint.com/FAQs/index.html)
    Cheers
    Tim

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    Re: restoring a jpeg file

    Quote Originally Posted by proseak View Post
    David,
    I'm not sure if CS4 will do this as i missed that one...

    Open all images in ACR, and save as DNG. This has two advantages - it gives you a lossless copy of the originals, it takes less space than Tiff, there's a lot you can do in ACR, and you can always change your mind; editing in ACR doesn't change the image as such, but applies edits, and appends these to the original file. Well, the DNG (...)
    Just a small nit: the original question was about jpegs, not raw files. DNG is intended as a RAW file alternative, with better specification, so not applicable to jpegs.
    I'm not even sure you actually [i]can[i] save a jpeg as DNG (other than as an embedded thumbnail), and I wouldn't want to try to reverse the demosaicing.

  10. #10
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    Re: restoring a jpeg file

    With reference to Peter's post (#7) and Remco's post #9, this has raised some questions for me. I have been aware that you can open and edit a jpeg in ACR but had never considered saving as a dng. I usually just hit "Done" and the edit data is stored in the jpeg's metadata. This means that if you open the jpeg again, the edit information is once again applied.

    However a quick check in ACR revealed that a jpeg opened in ACR can be saved as a dng and from a quick Google search it appears that this dng is a special form called a Linear dng (as distinct from a RAW dng). The Linear dng apparently saves the image as an RGB pixel raster rather than in raw format. (mosaicing is not re-visited). Not all Raw conversion software can open Linear dng's apparently. Here is the link I found.

    One of the interesting points that this article makes is that modern RAW converters do much more than raw conversion and indeed are now powerful parametric image editors for a variety of file formats. (Hence the popularity of Lightroom)

    Dave

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    Re: restoring a jpeg file

    Quote Originally Posted by revi View Post
    Just a small nit: the original question was about jpegs, not raw files. DNG is intended as a RAW file alternative, with better specification, so not applicable to jpegs.
    I'm not even sure you actually [i]can[i] save a jpeg as DNG (other than as an embedded thumbnail), and I wouldn't want to try to reverse the demosaicing.
    Yes, and you can do the same with flattened Tiffs. This means that there's a lot that you can do between ACR and Photoshop itself, without damaging the original.

    It's also one of the reasons I prefer Tiff to PSD until layers are needed - the ability to edit in ACR is itself valuable, and you can even discard the Tiffs in favour of DNG; the space saving mounts up.

    HTH

    Peter

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    Re: restoring a jpeg file

    Thank you to Dave and Peter for setting me straight on what DNG can do.

    And I can see the use of DNG for use with ACR or Lightroom. Otherwise, PNG would also work,
    and also give a considerable space saving (~40Mb in PNG vs. ~100 Mb in TIFF in my case).

    Just one question remains:
    can programs like photoshop or GIMP (pixel-level editors) open (Linear) DNG files?

    Regards,

    Remco

  13. #13
    dje's Avatar
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    Re: restoring a jpeg file

    Quote Originally Posted by revi View Post
    Just one question remains:
    can programs like photoshop or GIMP (pixel-level editors) open (Linear) DNG files?

    Regards,

    Remco
    Remco I tried opening up a "linear dng" (ie one saved in ACR from a jpeg) in Photoshop and found that it opens the file in ACR in the same way it opens any raw file. You can then move it into PS proper in the same way you can with any raw file. So basically PS treats it like any other raw file even though it doesn't actually contain data in raw format. I don't know about GIMP.

    Dave

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    Re: restoring a jpeg file

    Your existing jpg file is the best reference piece that you have. I don't see how converting it into another format is going to buy you anything other than take up more storage space. Use it as your reference image and rework and save the reworked images in whatever intermediate format that you like. I tend to leave them in Photoshop .psd until I'm done.

    When upsampling the old Photoshopper's trick was to increase the size by 10%, and do this up to three times. This was certainly valid in older versions of Photoshop as the algorithms seemed to give cleaner results with small incremental changes than with one large one. There are, of course some of the more advanced upsampling plugins that others have mentioned.

    The other argument about resaving in jpgs is also not quite true; yes you do lose data, but that happens on the first compression. Try opening and resaving the image (even a changed image) in Photoshop. You will find that there is no further data loss (assuming you are saving to the highest quality level).

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