DPI can someone explain?

[Izzy]

My T2i shoots at 240dpi, I think. I know that printers usually want 300dpi. Seeing that I have never had to print at 300dpi I want to know if I can "upres" and image to meet the 300dpi.

Could someone tell me the finer details of this? What should I know so I don't print unacceptable prints?

[kirbinster]

DPI has little if any meaning today. Your camera shoots at a given resolution in terms of pixels, lets say for arguement sake it is 4000 x 3000 pixels for a resolution of 12 megapixel. You can print that image at any size you want, the pixels per inch will be determined by the resolution divided by the size in inches. So it you printed an image that 20 x 15 inches it would be 200 PPI (or DPI in printing terms).

[teaking]

The only think I would add because as far as I know kirbinster is spot on, unless its an old style printing press the 300DPI thing is not all its cracked up to be. Most Inkjet printers will print at a default DPI so it will convert your file to its DPI. But if your printers want 300DPI come hell or high water just give him a file that size it probably wont be much different as your not adding detail.

[OsmosisStudios]

Originally Posted by Izzy

My T2i shoots at 240dpi, I think. I know that printers usually want 300dpi. Seeing that I have never had to print at 300dpi I want to know if I can "upres" and image to meet the 300dpi.

Could someone tell me the finer details of this? What should I know so I don't print unacceptable prints?

Depending on your RAW editor, you should be able to set the "DPI" when you edit you do your first edits.

[kayzar]

DPI means dots per inch, and is in fact only relevant to inkjet and laser printers. A digital image, is, as you may know, a bunch of coloured squares (pixels). When we select a DPI to print, you are basically telling the printer how many drops to put down per square inch. On a screen, we call this pixels per inch, or PPI, however, it has no impact on how an image looks on a screen, because screens a made up of a certain number of pixels, at a certain PPI. It basically refers to the density of pixels. The printing standard for design is 300dpi, however, the bigger you print, the lower the DPI needs to be as the print will not be looked at so closely.

[tuxcomputers]

In this day and age the only time DPI makes a difference is:

1. When scanning
2. Your talking to some one that has no clue

Check out these 2 photos, one has a DPI of 1, the other has the DPI set to 30,000, there is no difference in quality or file size, the DPI is just an arbitrary figure in the EXIF.



If I went to print either of these the software would go something like this:

1. He wants it what size.... 8x12, oh ok
2. Now what size is this photo... 2402x3589, oh ok
3. Now how many pixels per inch do I need to print that size at 8x12, divide that by that..... carry the 5..... oh ok, got it
4. bzzzzt, bzzzt, clunk, bzzzt... etc

At no point it time does it give a shit about the DPI that it is set to.

[teaking]

I have to say this subject is one that does confuse so many people including my self , PPI being the pixels per inch really doesnt matter, the size of your image is all that really matters as pointed out by tuxcomputers from the width and height the amount of pixels per inch is determined.

Now when we get to DPI thats set in your printer most modern inkjets let you choose 300, 600, 1200, some let you choose 1400 in reality your digital image does not have a DPI only the printed image does.

So as far as I understand it if we have an image that turns out to be 300PPI at the size its to be printed and the printer is set to print at 1200 DPI each pixel will be made up of 16 dots of ink or there abouts. Which also goes to explain a little why todays printing machines with high DPI resolutions can print good images at lower resolutions compared to older printing machines which had lower DPI resolutions as if we printed the same image on a printer with 300 DPI the image would consit of just 1 dot per pixel... I think thats right (300DPI x 300DPI) / (300PPI x 300PPI)