Dynax Digital Forums

Briefly, DPI quoted in the image file doesn't in itself make much difference and is primarily used to determine what the image thinks should be its full size.  If you print at a different size then the DPI will not be the DPI figure quoted.  What is important is the image resolution and the size that you print it at - the DPI on printing will merely be a consequence of the two, i.e. pixel length of the image divided by 18, or pixel width of the image divided by 12.

I believe that one rule of thumb is that the resulting DPI should be no less than 150, and ideally somewhat more than that.  Others with greater knowledge of these things than I should be able to give you more guidance!

Each printer has its own "sweet" spot in terms of dpi, above which little is gained in image quality (and burns up extra ink).  For my HP Photosmart it was recommeded to me that 220-240 dpi would be the optimum so I usually calculate a jpeg image size using 225 dpi, e.g. for a projected print size of 8" x 10" I will adjust the jpeg image to 1800 x 2250 pixels and set the printer resolution in the print menu to 225 dpi.  Check the chat rooms for your type of printer and see what others are using.

Stef i tried changing the dpi to 300 by also unclicking resample image on CS4. However to my surprise, when viewing the file on Print-Size on same CS4, it turned out to be very small compared to the one that previously was 72dpi. It only shows a 30cm print size!

It sounds like you are printing your own images so a few words from me.
Firstly I agree with all the advice so far.  I have an Epson stylus Photo R2400 and the recommended print dpi is 360 and I print most of my stuff at this.  You can get away with less than this and it then comes down to a combination of the size of your original file and how far away you are going to be when you view the print.  Get up close to some of these billboard images or the canvas images on the sides of trucks (lorries).  If you are in doubt, extract a portion of your image to fit a 6x4 or 5x7 paper at the resolution you need to print and check the quality.  I have printed A3+ from my images without a problem.  My A700 gives an image 4272x2848 pixels.  Using the 12" size (the maths is easier) 2848/12 gives ~235 ppi and this will be fine for a print...... john

Quote from: Stef. on March 14, 2010, 05:55:09 PM

Well 30cm is about 14 inches and that is correct! It's the right size for a good A4 print. Please double

What i can`t understand is how come that at 72dpi, clicking on print the photo file is far much larger than at 300dpi (30cm)?

Once you put 300 ppi under image size and unclick resample nothing visible should happen on the screen. You have merely re-distributed the same amount of pixels over you image. When you leave it at 72ppi and click print you basically tell your computer to put 72 pixels of the total amount of pixels that you have in your image over 1 inch. When you resize you tell you computer to now put 300 pixels over each inch of the print. Obviously as you have only a certain amount of pixels,  the image printed with 300 ppi will be smaller. I hope somebody can jump in and explain it in better words...
Stef.

Yes that's correct. You can lower the ppi but not below somewhere around 200ppi. With some images you can even get away with 150ppi. Alternatively, what I would do is: first unlclick "resample" and then put 240ppi > click O.K. Ope image size once more: this time do click resample > put 30 inches in under width and under resample method : click the down arrow and choose bicubic sharper (I know it says for downsampling but just do it ) You have then effectively upsampled your image.
Stef.

Well if you do your math...and I will NOT do the calculation (just got out of bed )...if you just print the image @30 inches you will end up with too little ppis to make it look really good. Are you printing yourself or are you giving it to a printer?
Stef.