Question about dpi

I read in a magazine some time ago that most digital cameras save the image at 72dpi and that this should be converted to at least 300dpi prior to printing.

I've tried this with the K10D and ist DS but can see no noticeable difference when I print.

The largest I normally print is A4 but normal 6x4 or a little larger.

I'm using a Minolta Magicolor 2300W colour laser set to 600dpi.

When I take prints to my local shop for proper printing I always convert to 300dpi.

Do I need to or can I just leave them at 72dpi?

The DPI setting in the picture file is a notional figure in some ways. If you actully printed an unedited file K10D file at 72dpi it woud come out at about 53x35 inches!!. If you have reduced it down to A4 you will be printing at a bit more than 300 Dpi anyway. Setting the DPI (without scalling the image) is really just a way of resizing it.

It does, however, seem odd that most cameras still leave that value as 72dpi. 300 would be better!

Hi Roger,

with the DS (I have a DL, so I'm happy with the figures) you get an image of 3008 x 2000 pixels. If you display at 72 dpi, which is what monitors are generally set to, then you get 72 pixels per inch, or an image 41" x 28" (aprox) open an image on your screen and set to 100% and you'll see. Printing is usually done at 300dpi, so you get a printed image, without any resizing (interpolating) of 10" x 7" or about A4 sized. To get a printed image greater than taht, the software used, either by you or the printer will interpolate, or add pixels to, the image in order to increase the finished print to the required size. To print smaller than the A4 native sized print, the software used will decrease the amount of pixels in a reverse procedure to the above.

If you actually print at 72 dpi, you'll get a very blocky/low resolution (relatively) image by comparison. If you'd printed at 72 instead of 300, you would have noticed.. The software would have corrected to a printing resolution.

Printing at more than 300 dpi, whilst it may sound great, will probably not result in a better image, due to the resolving power of the eye.

So, in summary, you'll get the best image from a 6mp camera at A4, and from the K10D at the proportionally larger size, A4 x 1/3 ish..

hope that helps, and the usual disclaimer that I could be completely wrong stands..

Cheers

Liam

Although used interchangeably much of the time, there is a difference between the ppi (pixels per inch) of the image in the computer and the dpi (dots per inch) of, say, an inkjet printer image.

As stated, 72ppi out of the camera produces an immense print size that, if viewed at the appropriate huge distance, would look fine. However, for normal sizes of print an image is interpolated in Photoshop to give the required size at 300ppi. There is no advantage in producing a 600ppi image as the eye cannot tell the difference. A 150ppi image shows on close inspection to be definitely inferior.

Now the printer puts down dots of ink per inch. If it put down 300dpi then every pixel would be represented by a dot of ink, which would be a very poor result indeed. I use 2880dpi, and hence every pixel is reproduced more accurately and the image quality is much improved. This applies to inkjet printers, laser printers and others may be a different matter again.

It's worth noting that Epson printers print at 720dpi by default - for the best results, this should be changed and a Custom setting made for Photo printing.

many thanks all - I'll give up converting them all to 300 dpi and let the printer fo the work.

It's got a 1200x600 setting so I'll use that

Hi Roger

I went through this problem last week as I was preparing my first batch of images for sending to ProAm Imaging for printing.

If you want to print an 8" x 10" @ 300ppi (or dpi if you wish) you need to first crop the image to the correct aspect ratio then resize without sampling so that the long edge of your image is 3000pixels, 10" x 300 = 3000, a rule of thumb calculation is, ppi x longest edge in inches.

Here's a few helpful links that I dug up....
http://www.scantips.com/calc.html
http://www.dynodan.com/image-new/preparing-images.pdf
http://digitalgalleryplus.com/fr_default.htm?/printing__image_resolution.htm

BTW, I fully recommend ProAm Imaging, 3 day turn around and the print quality is faltless.

Just to add another twist to this:
If you do your own printing etc then the dpi setting is completely irrelavent. You're concerned only, and 100% about pixels.

If, however, you give a JPG or TIFF to a publisher and they import it into Quark (or some other DTP) and you've got it set to 72dpi with 3008x2008 pixels then they'll curse you because they'll have to fiddle around and shrink your image to fit. Setting the right dpi helps the DTP software to sort its sizing out. If it's one or two images then that's not too bad, but if you're doing a product catalogue - you'd better set the dpi correctly

Matt

Surely you're still meaning ppi here, which should be at 300ppi for submission purposes, but also for printing at home.

dpi relates to the printer settings.

John,
I was referring to the EXIF designated "dpi" setting

Although what you say is correct about the variance between inkjet dots and pixels, it gets even more complex when dealing with postscript screening for litho and you start dealing with lpi (lines per inch) Still, the DTP packages generally deal with the EXIF dpi setting and default to "size = pixels / dpi" setting for the frame size. That's all I meant

Matt

OK I think I'm getting the picture

If I sent my images to a publisher (say Pentax Mag) to hopefully get some published then I should send them in 300ppi (or is that dpi)

If I'm doing prints at home then I'll just let the printer and PS do all the work.

I still don't really get the differance between ppi and dpi, PS only uses dpi

In very simple terms (cos I'm like that) is what I put above right?

Ta
Rodger

AFAIK, some Inkjet printers that promise 2400 dpi actually overprint the image so that (e.g.) Red and Cyan get printed onto the same dot or pixel. This means that you would not necessarily get better resoloution, but you might get truer colours.

When I submit pictures i do so at 300ppi and a print size as appropriate - either A4 or A3 depending on what it is.

The same applies to printing at home.

If I make a picture in Photoshop I make a printable copy at A3 and 300ppi. All these are saved as TIFFs.

If i want a pic for EPZ then I create a JPEG of 1000 pixels wide and 72ppi from the saved TIFF.

Further Reading for insomniacs!

http://en.wikipedia.org/wiki/Dots_per_inch

This just relates to printers and DPI.

Strange, my PS talks in terms of PPI - Pixels per inch.

To put it simply PPI is a measure that applies to the IMAGE and reflects, amongst other things, the amount of data available for further manipulation. (I did say I was being simple) - PPI X image size = total number of pixels in the image.

DPI on the other hand is a measure of the number of dots of inks the PRINTER places on the page.

So very crudely speaking printing a 300 PPI image at 1800 DPI means 6 dots of ink per pixel.

As has already been pointed out, this gives better rendition than printing out at only 300dpi. Incidentally, if my memory serves me correctly, the old dot matrix printers used 360dpi giving a very dotty image.

If you remember that PPI is an IMAGE measure and DPI is a PRINT measure you should not go far wrong. Much of the confusion comes from people who treat the two expressions as interchangeable - they are not.

So if you are scanning something, the result will be an Image. So you should think in terms of PPI of the resultant image. eg if you want a 10X6 image from a 10X6 document use 300 PPI.
If, on the other hand you want a 10X6 image from a 5X3 document then scan at 600PPI.
Do the maths, the resultant image in either case will be 3000X1800Pixels.

You worry about the IMAGE and let the printer worry about the print. Provided that you use Fine Quality, Photo Quality, or at least 1440dpi you should get satisfactory results.

Hope that helps
Graham

the problem is further compounded by the inkjet manufacturers using the "think of a number and double it" aproach when specifying what their printers are capable of. My Canon Pixma claims to be capable of 4800DPI. Does it produce better images than Johns Epson at 2880? probably not, and if it does it will be as a result of better driver software or clever ink technology and almost certainly not because of notional DPI capabilities.