Confused with printing

[Drihan]

Hi, ive been taking pictures for a while now with my Nikon D40 and want to start printing a few just for myself, but want them to look as good as possible.
I just have a few questions about how to know what dpi the pic is and how big my print can go. My camera is 6megapixels. And currently im viewing the picture in photoshop and the specs are as follow:

Pixel Dimensions
Width: 1600
Height: 2531

Document Size
Width: 16.93 cm
Height: 26.79 cm
Resolution: 240 pixel/inch

How do i know what the dpi is?

Thanks
Drihan

[teaking]

For greatest quality most sites and people seem to recommend 300 DPI the maximum print size from your picture would be as in your post, 16x26cm at 240 DPI its actualy a bit less most people state 300 DPI but even at 240 DPI you wont have a problem. You can even go to 150 but its personal preference I think the prints still look good. As for anything lower than 16x26cm no problems there the DPI will increase as the size decreases.

Its basically 1600 / 240 ( x 2.54 to convert to cm from inch) = 16.93cm

Although bear in mind viewing distance, larger prints generally are viewed further away and in these cases smaller DPI can be used as from distance the quality still looks good.

If pushed images can be enlarged with Bi-cubic sharpening methods in photoshop giving good results.

Like many things its all down to what your standards are but hope it gives you some information to base a decision off.

[Drihan]

Thanks teaking, that helped alot!! I thought that the 240 was the dpi. Oh and i tried changing it to 300 and then everything got bigger. And I zoomed in to 100% and the image quality still looked the same as with the 240. So can i change the dpi to 300 and then be able to print at a larger size that still looks good?

[teaking]

Glad it helped.

By changing the DPI what you are doing is increasing the number of pixels to do this pixels are made up well guessed at. Im not sure how photoshop does this through the standard image information dialogue. But I would recommend using the resizing tool and choosing the Bi-Cubic algorithm from the various options (sorry not a photoshop user im a GIMP man lol) I would say increasing your image over 200% is going to mean over half the image is made up pixels so be careful its probably best to think about the size you wish to print then work out how big in total it would have to be pixel height and width wise for 300 DPI (300 pixels in each square inch) then have a think "am I creating too many pixels?" if your happy then go ahead and interpolate (resize)

[BCampbell]

DPI, PPI, and printing can get really confusing because so many people use terms interchangably, both for input and output measures.

First, it helps to just stop thinking in DPI, this is how printers work, not your photo or photo editing. You'll (probably) never need to touch the DPI setting of your actual file. Let your printer or print lab worry about DPI.

You want to be concerned with PPI, pixels per inch. You are working with pixels, your printer is working with dots. The advice above is all good, generally "safe" resolutions are between 150-300ppi. The lower your resolution, the more likely you are to see the boundaries between pixels in the print, which is why digital photos printed too large look digitized or "pixellated".

If you're using a lab, just ask them, they'll tell you recommended dimensions for your photos. But, we can do the easy math at both 150 and 300ppi to find out what maximum size we can print your 1600x2531 image.

1600x2531 / 300 = 5.3"x8.4"
1600x2531 / 150 = 10.6"x16.9"

You can go in reverse, too, to find out what image dimensions you need to print to a specific size:

8"x10" * 300 = 2400x3000
11"x14" * 150 = 1650x2100

Since megapixels are simply the full count of pixels in the image, that's easy to calculate too:

2400px x 3000px = 7200000px = 7.2MP
1650px x 2100px = 3465000px = 3.5MP

You'll quickly see that if you want to print large images at very high quality, that will stand up to someone putting their nose right on top of it, you need lots of pixels.

20"x30" * 300ppi = 6000px x 9000px = 54000000 = 54MP

This is technically out of the range of even full-frame digitals right now, without a few tricks. But the need to print this big at this resolution is low for most of us, and you're talking over $50 per print anyway.

[Drihan]

Thanks for the replies! And thanks BCampbell! I forgot about the printers dpi. Now it all makes sense! Thanks for the help!

[BCampbell]

It's a kind of complicated issue that I haven't fully wrapped my head around yet. Would help so much if ppi & dpi weren't so easily confused and so often interchanged. Good luck!

[teaking]

Yeah I know what your all saying lol most graphics designers will say DPI when they should say PPI

I think the thing to do is when referring to anything digital up to the final print just take it as PPI its even in a lot of software it says DPI but theres no way it can mean it its like monitor resolutions we all know there PPI.

People just say DPI as its in the software packages they use and there used to that terminology. I dont really think it effects anything as long as people know that there talking about how many pixels are in an area and how that effects quality.

[filmoreha]

thanks for the awesome explanation! i was wondering about this myself.
so would you say that in order to print larger than the maximum pixels on our cameras AND keep the detail, we would need to also scale up the image?

[teaking]

If you want to maintain the 300 PPI/DPI in the final file for example it is required by your printers then you would need to upscale your image. But by doing so you are adding new information and the program is in effect logically guessing at this. Up to 100-200% increase Bi-Cubic, Fractal, and Lancoz give similar results after this fractals seems to give better results but at over 200% increase the image is more made up pixels than real pixels and hence the trade off.

But if you do need files to be in the 300 DPI/PPI range do the math and work out what size image you will need so then your only adding pixels you need. Photoshop and Gimp have a pretty good bi-cubic upscaler and you can either do it in one full stop, or in 25% increments some people recommend doing it in smaller steps.... I must admit im a one stop guy lol, but you could compare the two methods.