DPI versus Megapixels

[spetnaza]

Hi guys, great site.
Can someone please explain to me the difference?? I have been told by "salesmen" than the highest MP cameras are still only shooting photos that are 300dpi.
Doesnt really make sense to me.
Thanks

Daniel

 

[Anonymous]

DPI is usually used when speaking about printers or images on a monitor screen. Maybe his point was that there is no point investing in a 5mp camera if your output will be printed via a low-resolution printer or only viewed on a monitor screen, like photos for a web site. That statement taken at face value, though, makes no sense to me either.

 

[Len]

Might be a bit late, but DPI tells you the density of dots per a square inch as the name suggests. Megapixels simply means the number of absolute pixels (per million) regardless of size.

It actually gets a lot more confusing then this, so we'll leave it at that for now Ask if you have any other questions.

 

[Len]

BTW, the salesman doesn't make a whole lot of sense. A cheap 2 megapixel camera can shoot at 300 dpi, but the print size would have to be very small. A 6 megapixel camera can shoot at 300 dpi at a much larger print size. So your guess is as good as mine as to what the saleman meant when he said "highest MP cameras are still only shooting photos that are 300dpi." THat, in itself, is an inaccurate statement. You can print much higher then 300dpi if you have enough resolution to work with.

 

[wade1]

FYI anything shot with a typical digital camera these days, when saved in jpg mode on the camera is saved at 72 pixels/inch.


Wade

 

[tkhawaja]

The DPI the camera saves the jpg in does make a difference when you are trying to process many pictures with minimal retouching via software. Most digital cameras save their jpges somewhere between 75 - 100 DPI. My Canon G3 saves at 72 DPI. Strangely the highest DPI jpg saving camera I've found was the Kodak EasyShare. It saved at 116 DPI therefore it just printed out better than some of the higher MP cameras. In our situation this worked out well, we were doing thumbnail prints of car ads. When you're doing hundreds of pictures it helps out a lot if you can go directo to print instead of having to do processing on every picture.

 

[azcaddman]

For more than you may care to know about this subject, see the following articles on Luminous-landscape

Understanding Resolution
http://www.luminous-landscape.com/tutor ... tion.shtml

Understanding Digital Camera Resolution
http://www.luminous-landscape.com/tutor ... myst.shtml

and finally

Counting Megapixels— All Megapixels Are Not Created Equal —
http://www.luminous-landscape.com/essay ... ing1.shtml

 

[spetnaza]

Hi all, thanks very much.

A confusing topic, but one worth discussing.
A few questions for the knowledge base.......

Is there a direct relationship or ratio between pixels per inch and Dots per inch ?? ie 100ppi is equal to 80 dpi etc etc.

Is there a direct relationship between ppi as seems to be used by the digital imaging hardware (scanners and cameras) and megapixels?? ie is a 5 mp camera putting down more ppi on a given photo than a 2mp taking the same photo?? If so, what is the equation/ratio??

Finally, im confused, but i think a pixel is a unit of measurement, especially since it can have different sizes etc, so is it fair to say that a PIXEL can have a said RESOLUTION, ie each pixel has a resolution of 100dpi for instance.

By the way, i dont want to sound rude or ungrateful, i am very grateful, but there are some conflicting replies to my original post, so I really think that this is worth discussing further to a resolution, if at all possible.

Len you have told me that photos can be taken at 300dpi. That is describing the resolution of the photo before it is printed (printing is irrelevant i think in this discussion at the moment) regardless of the mp capabilities of the camera and regardless or the mp setting of said camera.

tkhawaja then has posted that 112dpi is the maximum of any photo on any camera, again regardless of mp capabilities or settings.

Oh boy is this getting confusing.

Daniel

 

[tkhawaja]

tkhawaja then has posted that 112dpi is the maximum of any photo on any camera, again regardless of mp capabilities or settings.

That is not what I stated. I said the highest I had found was jpegs being saved by a digital camera were 116 DPI. We just found that the higher the DPI the jpeg was saved in the better it printed out for our purposes.

 

[spetnaza]

my apologies, new member, it came across alot worse than i had hoped

 

[azcaddman]

try doing a search on www.dpreview.com ... under forums, for "dpi vs ppi"

they explain it much more clearly than I can

http://forums.dpreview.com/forums/read. ... ge=1842799 would be a good start