What is DPI ?

[canon-S5IS]

I know that ... but why ...

I use a digital camera to take a picture of an object about 5 inches from the camera. I use NO zoom. Then, after downloading the image to my PC, I right click on the file, and display its properties.

Windows says it is 3264 pixels wide and 2448 pixels in height. It also says both the horizontal and vertical resolution is 180 DPI.

I load the image into Microsort Paint, and it still says the image is 3264x2448. I change Paint to display image attributes in inches, and it is said to be 34" x 25.5".

The actual object is roughly 6" by 4.5".

What is that figure of 180 DPI ? How is that determined ? If the object is truly 6" wide, why isnt the DPI reported as ~544 ?

 

[MX962]

it is an irrelevant number asigned by your computer it doesnt affect a thing

 

[-GDconcepts-]

DPI stands for Dots Per Inch. It is a term normally used for scanning and printing. The higher the DPI, the higher the quality. If the computer is telling you the DPI, I wouldn't really worry abou it. Also, I would try and find another program to edit with. MS paint lowers resolution once it has been saved in that program. 3264 x 2448 is a pretty large resolution. You can print a 4x6 with that. You could also print a decent 24x36.

 

[davebmck]

Like GDconcepts said, DPI is dots per inch and relates to printing. Your photo software should be displaying PPI or pixels per inch. If your image is saved at 180 ppi, you can divide your pictures pixel dimensions by 180 and you will get your picture size. In your example the 3264 x 2448 pixels would give you a picture size of 18.1 x 13.6.

You want to print with a resolution of at least 240 ppi, 300 is better. If you change this picture to 300 ppi the picture size would be 10.9 x 8.2. Most photo software will allow you to resize the picture while maintaining a given resolution. Paint is not a program I would suggest using. Your printer software would probably work better than that.