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  1. #1
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    Default Relationship between megapixels, Megabytes and dpi with regard to printing quality

    I want to print some of my photos in large size on stretched canvas, e.g. 60cm x 90cm.
    The printing guys insist on a print quality of 230dpi ... BUT I AM NOT PRINTING !!
    The only info I have from my photos are the MEGAPIXELS (e.g. 2100 x 1900 pixels) and the MEGABYTES (e.g. 5.2Mb).
    I also understand thet the photo is composed of PIXELS and therefore the MEGAPIXELS are important for the printed results.
    I also understand that to print a 60cm x 90cm from a 250kB original will look bad....Or am I wrong ?
    Can someone please explain the connections between the embedded photo data (Pixels, Megabytes) and the print parameter of 230 dpi for instance, and what is really important for larger prints.?

  2. #2
    Frequent Member elsahoffmann's Avatar
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    Default Re: Relationship between megapixels, Megabytes and dpi with regard to printing qualit

    The printing guys insist on a print quality of 230dpi ... BUT I AM NOT PRINTING !!
    i don't know what you mean by that statement

    90% of my photos are not printed - and I have very high res images - so I dont get into this issue - but what I can tell you - you can't print an 60 x 90 from such a small file. The detail just wont be there

    Also - you dont like at file size (250kb) you look at pixel dimension at a specific resolution

    But I think others may give you better input than I can
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    Default Re: Relationship between megapixels, Megabytes and dpi with regard to printing qualit

    Thanks Elsa
    I don't plan to print from a small file but the printing shop indicates that I must have an image of minimum 350 dpi.
    I would like to know how 250 dpi relates to pixel counts (or size in Megabytes).
    The small size I gave was just an example and I am aware that the print 60cm x 90 cm will not be adequate or satisfactory.
    A large print costs something like R 800,- and I simply want to make sure that the print will be sharp and fine BEFORE I place a printing order.
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    Last edited by Gerd; 30-03-2018 at 08:37 AM.

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    Frequent Member elsahoffmann's Avatar
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    Default Re: Relationship between megapixels, Megabytes and dpi with regard to printing qualit

    Gerd

    Printing is a loooong subject - Books have been written on this subject. Not possible to repeat it all here.

    Suffice to say: 230-300 is more than sufficient for printing - often 230 rather than 300 especially IF you print very big, and sometimes on canvass as well.

    (dots per inch is the amount of ink dots per inch that is laid down on paper in printing - so 72 dpi will give you 72 dots per inch printed - whereas 300 dpi will give you 300 dots per inch - which means more ink is laid down for a clearer print)

    What is the exact size of your image? and on what camera did you shoot - and is it full res or did you crop?

    You can also ask the printer do do a sample print where they take a portion of the image (eg jumbo size portion from somewhere in the image) and print that. thats a test print so you can check with your printer
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    Default Re: Relationship between megapixels, Megabytes and dpi with regard to printing qualit

    Hi

    I recently had some large prints made, and the printer gave me the same info, he must be able to print the required size print at a resolution of 300 pixels per inch, or 120 pixels per centimetre. I had to resample my images, (not resize) to get them to the correct image size, in my case about 9000 x 5000 pixels for the images. The resulting print quality was excellent. For the 90 x 60 prints mentioned in your post it would be around 10800 x 7200, that’s a large 77 megapixel image. Perhaps more if you have several layers in the image.

    For interest I post processed the images in Photoshop CC, and then resampled the images using the “Preserve Detail 2.0” resample algorithm in PS CC to get the correct size, and then sharpened the image. An older method was to resample the image in 10% increments until the desired size was reached.

    You also mentioned Mbyte file sizes in your post. I say this under correction but there is no direct correlation between image size in pixels, and file size in Mbytes. A RAW file and a Jpeg file with identical pixel sizes will have different file sizes. In my case a RAW file is around 23 Mbytes, an identical sized Jpeg is around 6 Mbytes, yet both have 18 megapixel images.

    There may be other methods of obtaining high quality prints from smaller images, but that’s what my printer needed so I followed his instructions.

    Jim

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    Default Re: Relationship between megapixels, Megabytes and dpi with regard to printing qualit

    Hi Jim and Elsa
    Thanks a lot for the info.
    Yes, I know it is a looooooong and equally wiiiide subject but every little info helps. I shoot with Canon 6D (mostly) and Canon 1D Mk4 (wildlife) and shoot in RAW only.
    I thought that there is a direct relation between Pixel Qty.and (large) print size and so it appears I will have to climb into Post RAW processing.I obtained Cs6 very recently and now I MUST get aquainted with it speedily.
    Final question: To your knowledge is there a printing software available for printing directly from RAW ?
    Thank you again for clearing the matter up to a great extent.
    Gerd

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    Default Re: Relationship between megapixels, Megabytes and dpi with regard to printing qualit

    Quote Originally Posted by Gerd View Post
    Final question: To your knowledge is there a printing software available for printing directly from RAW ?
    No, a raw file is just data that needs to be converted via software. If you're worried about quality issues arising from compassion just save them in an uncompressed format such as a TIFF.

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    Default Re: Relationship between megapixels, Megabytes and dpi with regard to printing qualit

    Hi Gerd

    Not sure if you have used a previous version of Photoshop and upgraded to CS6, or if Photoshop is new to you. You may already have seen that Photoshop will open a RAW CS2 file in Adobe Camera Raw, (ACR) then allow you to open the image directly in Photoshop proper. I use ACR to correct any obvious highlight and shadow issues, the rest of my post processing is done in Photoshop proper.

    I am lucky enough to have a friend who is a Fellow of the SA Photographic Society and a Fellow of the Royal Photographic Society. She also runs seminars in the UK on using Photoshop for photographers who entering panels to become either an associate or a fellow of the RPS. She took me through a complete workflow on Photoshop post processing that proved to be a solid platform to build on.

    I looked at many sites on U tube for additional information and skills, but one of the best resources I found was www.photoshopessentials,com. The site has PDF documents that cover almost every aspect of PS post processing, the info is easy to understand with lots of examples. You can browse the site and read all the PDF’s, or you can for around $20 download all the PDF’s.

    Enjoy using PS, I love it, keeps the grey matter working for an old guy like me

    Jim

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    Default Re: Relationship between megapixels, Megabytes and dpi with regard to printing qualit

    Many thanks Jim and Norm de Plume,
    At last I got answers and I now can start to torment my grey matter with Photoshop.
    Can images shot in RAW be transformed into TIFF without any loss of quality and can TIFF images also modified / changed / manipulated in photoshop ?

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    Default Re: Relationship between megapixels, Megabytes and dpi with regard to printing qualit

    Hi Gerd

    You can convert a CR2 file to a TIFF file with zero loss in quality. In ACR you have several options. At the bottom of the ACR screen there are for buttons, “Save Image” “Open Image” “Cancel” and “Done”

    Save Image – if you are happy with the adjustments you have made in ACR and do not want to go to PS, clicking the button will open a dialog box allowing you to save the image in a range of file formats, including TIFF.

    Open Image – clicking this button will open the image in PS in CR2 format. You can make adjustments and when you save the image the dialog box will give a choice of file formats.

    Cancel – simply closes ACR without saving any adjustments.

    Done – closes ACR but saves any adjustments to the CR2 file without giving you any file options. When you reopen the CR2 file all the previous adjustments can be seen and redone. The adjustments are none destructive.

    If you hold done the Alt key when clicking Open Image, ACR will open a copy of the image in PS.

    Hope this helps

    Jim

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    Default Re: Relationship between megapixels, Megabytes and dpi with regard to printing qualit

    Hi Jim
    A ton of thanks for your help. Makes me feel much much better about the subject , now that I have answers.
    Gerd

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    Default Re: Relationship between megapixels, Megabytes and dpi with regard to printing qualit

    Qimage can print directly of raw files and is excellent at retaining detail in large prints.
    Enjoy Global Warming while you can, the next Ice Age is on its way........

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    Frequent Member elsahoffmann's Avatar
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    Default Re: Relationship between megapixels, Megabytes and dpi with regard to printing qualit

    My question is this - why would you want to print from RAW?
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    Default Re: Relationship between megapixels, Megabytes and dpi with regard to printing qualit

    I do not want to print from RAW, it was merely a question simply because of the available RAW image sizes. I am starting to get deeper into more details concerning different image files (Jpeg, TiF and TIFF, Raw and the resultant image definitions.
    When playing around with RAW images (I began using the out of camera CANON RAW PHOTO EDITOR ) I noted that when converting from RAW to JPEG the file size reduced from e.g. 25 Megabytes to 5 or 6 Megabytes and with a JPEG file the editing possibilities are severely limited as compared to RAW editing via the Canon Software.
    Then I read some time ago that Images are best stored as RAW files because all original image parameters are retained in "eternity".
    Then I read that converting RAW into TIFF also conserves all image qualities , however when I converted a 23 Mb RAW into a TIFF image it showed suddenly 52 Mb This is throwing me around a little because everyone is looking for as small as possible file sizes for storage but TIFF contradicts this because files become bigger than Raw.
    MY VERY ORIGINAL QUESTION WAS: Can i deduce from the file size of an image whether a large print of the 60cm x 90cm variety would be appropiately sharp or in other words: For a print of the aforementionsd size, what should be the ideal or sufficient parameters of the image ? The answer was PIXEL COUNT and NOT MEGABYTES if printing would be done with around 300dpi.
    I also deduce that the pixel count of a RAW image and that of a converted JPEG or TIFF image are identical, which in conswequence means: The larger the desired print with acceptable sharpness and definition, the more Pixels are neccessary.....Correct ???

    I did not know about the "re sampling" of RAW images in PS, which means in essence "one is able to increase the pixel count of an image". CORRECT ??? My new question would be : HOW FAR CAN THIS BE TAKEN ???
    Anyway, I will have to climb into r my CS6 with Gusto to discover more and more about the extremely large subject of modifying / treating / changing / enhancing / correcting / etc etc etc./ images digitally.
    What a subject !!!
    Thanks all for your input, I feel like a newborn idiot right now .......

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    Default Re: Relationship between megapixels, Megabytes and dpi with regard to printing qualit

    Hi Gerd
    When I mentioned converting CR2 to TIFF files in ACR, I forgot about the instant increase in file size, I only convert to TIFF when post processing. If you work with multiple layers in PS the files can get very large.

    It took a while to understand that enlarging an Image simply by resizing just increases the size of the pixels with a loss of quality. Whereas resampling adds pixels to the image maintaining quality levels of the image.

    I use PS CC with the Preserve Detail 2.0 algorithm for increasing image size. I have pushed it the 300% without a noticeable loss of quality.

    I only sharpen the image once I have it at the required size. I used to use LAB sharping in PS but now I use the High Pass filter on a layer. Using the blend modes, opacity sliders, and layer masks you can tune the sharpening exactly to your taste, You can apply sharpening to selected parts of the image or even different levels of sharpening to selected parts of the image. It may sound complex but it is very, very easy. I’m an old guy, I can’t even spell complex.

    Jim

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    Default Re: Relationship between megapixels, Megabytes and dpi with regard to printing qualit

    Hi Jim
    Thanks for all the explamations and tips. Very vert much appreciated.
    I am an old guy too but I have no problem with spelling kompleks..........

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