What determines DPI (in camera)

[tomscott]

<p>I am pretty much a novice with digital photography and not sure what I am doing. I just bought a Canon G12 figuring that it would be a good way to get my feet wet and, would be a pretty good camera for travel. After I download files from SD card to computer and open them in editing program (I am using Irfanview at the time) the pictures come out at 3648 X 2736 pixels but they are at 180 DPI. What I mean is, when I click on Resize/Resample, that is the numbers that I get. When I used my Nikon L18 they would come out at 300 DPI. Are these the actual Dots Per Inch that is coming from the camera or is that an arbitrary number that I can change at will?</p>

[leighb]

<p>In Irfanview (excellent program) you can change the DPI setting in the resize window.</p>

<p>But that's really only meaningful if you try to print the image. If you view it on the computer monitor with the auto-resize function enabled (the default), it will fit to the screen regardless of the DPI setting.</p>

<p>For example, if you have an image that's 600 pixels wide and set it to 300 DPI, it will be 2 inches wide when printed. If you set it to 150 DPI, it will be 4 inches wide, assuming the DPI setting honored by the print driver.</p>

<p>- Leigh</p>

 

[ellis_vener_photography]

<blockquote>

<h1>What determines DPI (in camera)?</h1>

</blockquote>

<p>The way the engineer at the factory programmed it. </p>

<blockquote>

 

</blockquote>

[tomscott]

<p>So are you saying that DPI is a function of the printer and not the camera? I basically understand that to print a photo 8 X 10 at 300 dpi it would need to be 2400 X 3000. Are you saying that at 3648 X 2736 the program chose 180 dpi to make it fit the screen?<br>

Ellis, like I said this is new to me, maybe I didn't ask the question correctly?</p>

[leighb]

<blockquote>

<p>So are you saying that DPI is a function of the printer and not the camera?</p>

</blockquote>

<p>As Ellis said, it's how the camera is programmed. It's just a value that's stored in the digital image file. It has no relationship to the real visual world, except when you print the photo, or if you try to display it at full resolution on a computer screen.</p>

<p>If you have a computer screen that's 1024 x 768 pixels, and you try to display an image at full resolution that's 3072 x 2304 pixels in size, the image is three times the size of the screen on both x and y axis, and you'll have to scroll to see the whole thing.</p>

<p>But this is not "DPI", which means Dots Per Inch. It's just dots (k.e. pixels). The dimension, i.e. the size of your screen in inches, has nothing to do with how the image is rendered.</p>

<p>- Leigh</p>

[lornesunley]

<p>Cameras do not do DPI. A sensor has a certain number of pixels, that's it. DPI is a construct that is used when printing an image (or sometimes when displaying it).</p>

[tomscott]

<p>Thanks to all of you for your help. So the fact that it comes up 180 DPI has nothing to do with anything I need to be concerned about then. If I want to print a photo, I just change the DPI or the Pixel size (or both) to match the size of the print I want to make? IE: if I want a 4x6 print I need 200 dpi at 800 x 1200 or 300dpi at 1200 X 1800? </p>

[leighb]

<p>You CAN resize it appropriately but you don't NEED to do so. The printer driver software will do it automagically.</p>

<p>There can be a difference in quality, however. Irfanview has an excellent resize algorithm (if you use the slow option). So you might get better results doing it yourself. Always select a DPI value that's native for the printer (300 or 360 or whatever). You can specify image size (inches) and DPI independently.</p>

<p>- Leigh</p>

 

[mariosforsos]

<p>Like it has already been mentioned, the camera sensor produces an image with specific dimensions, measured in terms of pixels, say 4000 by 5000. These are ALL the pixels you have. From these, you can create a printed image of 40 by 50 inches if you pack those pixels with a 100dpi density. If you pack them at twice that density (200dpi), you would get a 20 by 25 inch image. If you pack them at three times that density (300dpi), you would get a 13,3 by 17 (approximately) inch image.</p>

<p>DPI is just a notation/concept used to define the resolution of the final print, i.e. how fine (or not) it is. What the various pieces of software are doing is, essentially, assigning an arbitrary "packing" value to the pixels they're working with as an indicator, nothing more.</p>

[digitaldog]

<p>And not all the pixels in an array are used to capture image data (some are used for white balancing and other processing tasks). When looking at the spec’s, be careful to view those that define image (capture) pixels from the full array. </p>