A question about dpi

When you use Canon's Zoombrowser, the default is to 72dpi which of course is the maximum veiwing resolution of most monitors. Which is why it defaults to that. What about for printing though? of which most people recommend 300dpi.

I know you can convert an image with photoshop up to 300dpi... but that "unnaturally" stretches to 300 doesn't it? It would not change the fact that it is a 72 dpi picture.... just simply made bigger... right?

The information saved in a RAW or .CR2 file is pure, therefore is there a way to change the default conversion from 72dpi to 300?

To convert a photo to 300dpi you aren't necessarily stretching it. It depends on the size you're printing.

300 dpi at 20x30 would obviously need to be stretched, BUT you do not HAVE to print at 300dpi.

Larger prints are viewed from further away, you don't stand up next to a print that is 20x30, you stand back so you can get away with printing a full size 18mp file without upsizing it at all. It won't be 300DPI but that doesn't matter.

A smaller print like an 8x10 can be achieved with a 10mp sensor without any upsizing at 300DPI.

Here is an interesting article: http://www.pcworld.com …s_largest_print​_size.html

Edit: here is ANOTHER article that may be of assistance: http://www.bythom.com/​printsizes.htm though you still need to keep view distance in mind.

First off, monitor resolution hasn't been 72 ppi for 30 years, That was the number Macs used in the 1980s because in some ways it made graphic design easier. Microsoft favored 96 ppi. MS won. The fact that the Exif standard calls for filling that field with 72 when no real resolution is known is an anachronism. Modern LCD monitors range from 90 to 110 ppi and any image on a screen will be displayed at the resolution of that particular monitor, without any regard for the number in the Exif.

As regards prints, what is important is the REAL ppi, which is the available pixels divided by the inches of print they have to cover. It is a derivitive number determined by pixel dimensions and print size, and by nothing else and until somebody has decided what size the print will be, it can have no meaning. If I have 2000x3000 pixels and I put them on 8x12 paper the real ppi will be 250, no matter what is written in the Exif. The Exif number can easily be changed from 72 to 300 to 3000 - the reality that I am putting 250 pixels on every inch of paper is unchanged. Real ppi can be used as a guide to predicting the quality of the print: 180 to 200 borderline, 200 + acceptable, 240 + good, 300 optimum, but since ppi is a second order number derived from the number of pixels in the image, ultimately pixels are the only thing that matters.

Both very informative and concise explanations. Thank you both.

The reason I ask is that I'm entering a couple of my photos into contests. Some of the rules state, if an image is chosen. The photographer must provide a high quality jpg

My camera is your basic bottom of the line SLR with 10mp

It just got me thinking about dpi

In the digital age if you aren't printing you would refer to ppi. A 300 ppi image at 8 x 10 is a image that is at least 2400 x 3000. Any higher and you are higher than 300ppi at 8 x 10.

Sdiver2489 wrote in post #12336035
In the digital age if you aren't printing you would refer to ppi. A 300 ppi image at 8 x 10 is a image that is at least 2400 x 3000. Any higher and you are higher than 300ppi at 8 x 10.

excellent uncropped photos are 3888x2592

So basically the exif saying 72dpi is totally irrelevant, is the jist of it right?

Crimzon wrote in post #12336092
excellent uncropped photos are 3888x2592

So basically the exif saying 72dpi is totally irrelevant, is the jist of it right?

Yes, the printer/software will do the conversion when you set the output print size. Alternatively, photoshop will set it if you set the desired photo size.

Even then, 300dpi is vastly overrated.

I cover DPI a little in this FAQ.

Ok thanks Tim. That helped

Thanks to everyone I now have a pretty good understanding of it. I'm no longer confused, or worried about only having 10mp. That still wont stop me from wanting a better camera though.

I have a 30" print made from a 6MP image, it looks awesome. I have a 50" print made from a 12MP image, it looks awesome too. I suspect I could do 50" with 6MP and it'd look great.

Make a good image and people won't nitpick the details.

Tim's link points out difference of PPI vs. DPI. As he stated, "dpi stands for dots per inch, and it's a physical measure of how many dots go on a piece of paper. We don't care about this. The output device could be a continuous tone printer, a 250dpi minilab, or a 4000dpi inkjet, we just don't care."

To illustrate this point, the embedded value in EXIF might have '72 dpi', I can print it on a Canon printer which assumes 300 dpi, or an Epson printer which assumes 360 dpi, and never have touched my actual photo file to change the EXIF value which is embedded into the file!
Furthermore, I might use a Canon ip100 printer whose head and paper advance is capable of 9600 x2400 dpi per its specifications, while I might also use a Canon iP2702 printer whose head and paper advance is capable of 4800 x1200 dpi per its specifications and never have touched my actual photo file to change the EXIF value which is embedded into the file!

DPI specification is that irrelevant. DPI came about as an output device specification in the days before digital photography, as an offset print setting for 'screen' mesh size, which affected the quality of printed photos on pages like newspaper (low DPI) vs. glossy magazines like National Geographic (high DPI).

One complication to this is the fact that often we use software which calls it 'DPI' (wrongly) when the software is deterimining 'PPI' (Pixels Per Inch) in its export of JPG from RAW conversion, as the total pixel count is determine by the product of print size x 'DPI'...a 5184x3456 pixel 7D photo intended to print a 4x6" photo at 200 ppi has '200 DPI' as the output parameter (not PPI) in some software, and the software outputs a JPG file of 800x1200 pixels as a result...which is '200 PPI' in the final print, not '200 DPI'. And pro labs often repeat this same confusing error because their software is similarly AFU.

Lastly, let me comment that I often use Zoombrowser to do 4x6" printing on my home printer with a 3888x2592 pixel (40D) file, using a file with 72 dpi embedded into its EXIF, and I also might send that same file to Costco for printing 8x10" with the same 72 dpi value in the EXIF, and I get the right sized output and never touched the embedded EXIF value. Nor have I changed the file's pixel sizing (from 1200x1800 to 2400x3000, to keep a 300 DPI or 300 PPI output in the 4x6 or 8x10, respectively). The only time I bother with counting pixels is if I want to have a large print made (e.g. 16x20") and then I resize the file to 4800x6000 pixels in order to meet the lab's 300 PPI minimum (although they might wrongly state it as a '300 DPI minimum'