500pts: dpi/Resolution output for digital printing?

Posted on 2006-04-05
Last Modified: 2010-04-03
Hi there,

can anyone help?

I have been asked to print some Pictures out using a digital printing shop/service. These JPG's are currnetly 72dpi and anywhere from 800 x 600 to 1600x1000

I believe i need to convert these to 300dpi for output work?? is this correct? Otherwise it would look very bad quality...

If so then the resolution will change for example 800 x 600 will drop to xxx by xxx for example..

The thing i don't understand is, how do i tell what size an image will be i..e in inches or cm on the final output on the piece of paper?

Can anyone shine any light on this for me?

Also i believe i am correct is saying 300dpi for output is best, but maybe i am wrong?

And i have tried in the past by increasing the DPI i.e. from 72 to 300 and using bicubic conversion or similar so that the resolution doesn't change but i always found this to produce really bad results.... of course i may have been doing it wrong??

Any advice or help would really be appreciated

thanks in advance

Question by:ianinspain
    LVL 38

    Assisted Solution


    First of all, always ask your printshop about what formats and resolutions they need :)

    You are generally correct in your comments above. If your original is 1600 X 1000 in 72upi (units per inch), you can print an image of 22.22" X 13.89" with 72dpi (dots per inch). If you change the DPI to 300, the same number of dots will be printed, but they will be a lot closer together (because you are fitting 300 of them into an inch, not 72), so your final image will be 5.33" X 3.33". If you need to keep the same physical dimensions (22.22" X 13.89"), you need to extrapolate all the extra points with bicubic sampling, and as you say, that amount of upscaling can produce pretty poor results.

    In photoshop, to rescale the number of dots per inch, while allowing the print area to decrease, go to Image -> Image Size and unclick the "Resample Image" checkbox. Then enter your desired resolution in pixels per inch.


    Author Comment

    thanks for your comment lherrou...

    Do you think 300dpi is sufficient for printing .. or do you think i can drop to 200 ?? that way i can have a bigger image??

    Thanks again

    LVL 38

    Expert Comment

    If we're talking photo paper, you can probably go as low as 233 or even 200, larger images are typically viewed at a greater distance, and therefore the dpi isn't quite as critical. I'd still contact the printer, or send a trial image and see what the results are like.

    LVL 4

    Assisted Solution

    There is also a big difference in the printing-methods used.
    I own a small photo-printer with accesoire camera, wich shoots pictures at max 640-480,
    the printer itself is a sub-dye system. It heats the solid ink-lint and transfers it directly to special paper, and gives a very neat photo-graph, though with a white-border. absolutely no dots visible. The printing-method is advertised as a 148 dpi resolution.
    If I print these photo-graphs with a inkjet, same output-size, the quality is not good.
    So it is also dependant on what type of printing they use,
    inkjet, color-laser, wax-blocks, wax-foil ect ect,
    So, follow the advice from lherrou, and ask if they can print a trial-image for you, and for this, send the smallest (least pixels) picture
    LVL 26

    Assisted Solution

    by:David Brugge

    It all depends on how these prints will be used. A 72 dpi image will look as rough as sandpaper when you enlarge it up to 300 dpi if you are looking at it at arms length or closer. If they are going to be posters viewed at a distance, no one will notice. For the most part, it doesn’t do any good up upsample the images before printing them. The original images only have a certain number of dots in them. If you use a program to enlarge them, it will fill in the extra dots with it's best guess as to what should be there.

    If you print them as is, the printer will fill in the dots with its best guess as to what should be there. You aren't going to magically get any more information in them one way or another.
    The only difference is that you can control the sharpening just a little bit and adjust for contrast a little bit if upsample (go from a low resolution to a higher resolution) yourself, but many times this isn't worth the effort and if you don't know what you’re doing, you can make the images worse.

    In my work, I take images with my 35mm digital camera and enlarge them to 48" X 96" Te printed resolution is 125 dpi. These hang from the ceilings of stores and are viewed from a distance of 8 to 20 feet. they look perfectly sharp at that distance, but close up, you can see every pixel is about half the size of a dime.

    My advice is to discuss it with your printer. They have had a lot of experience with their machine and know what it will do. You night even take a sample image and run a small section at two different resolutions as a test just so that you will know what you are getting.

    David B
    LVL 16

    Accepted Solution

    Hi Ian,

    I recently moved out of the printing industry after over 15 years. I agree with everything the others have said so far.
    Here are two options you might consider, one free, one which would mean spending money.

    1) Free: Sometimes you can get away with res-ing up an image. Lets say you have an 8.5x11 at 72dpi. You can try to change the resolution to 300 dpi without changing the size. I'm not at my workstation, so I can't walk you through it but I recommend using 'Nearest Neighbor' in the dialogue box. (But you can experiement as well). With SOME images that don't have a lot of fine detail, you can get away with this, although you might have to play with the unsharp mask too. Iffy, but free.

    2) Pay: If this is really important quality-wise, you might consider purchasing Genuine Fractals software:

    We have had great results when we had a low resolution image that had to be printed at larger sizes. I highly recommend this product when you have no other option.


    Author Comment

    thanks everyone for the comments... it was much appreciated


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