Need help setting DPI on Canon 350D

[Big Mike]

Yes...when you change the PPI...it does change the 'size in inches'...but that's a different issue (at least I think it is...I forget what we were talking about too). If you want to know the print size...then change the PPI to 300...and it will divide the image size (in pixels) by the PPI and give you the print size.

It's up to you to know that for good quality prints...300 pixels per inch is what you want to shoot for...but it all comes back to the size of the image.

 

[markc]

The point I was getting at is that size of image in pixels, size of image output (either screen or print), and DPI/PPI are tied together in a similar manner as ISO, aperture, and shutter speed. DPI/PPI alone tells you nothing about the quality of an image without knowing the rest of the story, just like knowing just the aperture doesn't tell you what an image's exposure is.

Actually, it's even less important than one of the exposure elements. DPI/PPI is made up of the other two image elements: Dot/pixels and inches. It's just telling you how many dots/pixels there are in an inch.

When a image is in a digital file format, the only element that has bearing is number of pixels. There are no inches, so the other two elements mean nothing. When it's put on a screen, they now have bearing, but the number of inches changes depending on what system the image is being displayed on (size of monitor and it's current resolution), so they don't mean much. When you make a print, you finally have a solid "inch" measurement that isn't going to change on you. Now you can use the PPI to see if you are likely to get a quality image. If it's 300 PPI or more, you are likely to be happy with it. If it's 125-300 DPI, it's going to depend on your tolerance for such things. Under 125 DPI and some people are likely to have issues with the quality. That's just a rule of thumb, though. It all depends on what you are printing on, the image, your eye, and other factors.

 

[Digital Matt]

I think the original poster was confused in thinking that the 72 DPI in the jpg from the XT meant that it was a low res file.

Dpi is meaningless, until you want to print your file, in which case you should be resampling the image to the desired image size, and setting the DPI to 300 DPI at this time. This all should take place in software.

 

[Big Mike]

I think the original poster was confused in thinking that the 72 DPI in the jpg from the XT meant that it was a low res file.

We see this often...a lot of people are confused by it.

 

[markc]

in which case you should be resampling the image to the desired image size, and setting the DPI to 300 DPI at this time.

I usually disagree with this approach, as it either bloats the file size without adding detail (if you are enlarging), or you are deleting detail (if you are shrinking). The only time I think it's warranted is if the printer being used actually requires a 300 DPI file to print correctly.

I've seen people talk about staged enlarging, but I remain unconvinced, as I haven't seen any good examples yet.

 

[shingfan]

I usually disagree with this approach, as it either bloats the file size without adding detail (if you are enlarging), or you are deleting detail (if you are shrinking). The only time I think it's warranted is if the printer being used actually requires a 300 DPI file to print correctly.

I've seen people talk about staged enlarging, but I remain unconvinced, as I haven't seen any good examples yet.

i'm not sure if you alwys need exact 300 DPI image...but for sure with walmart.....if your image is 10MP and you want to print 4x6...better size it down before taking it for print.....they dotn come out nice fi you give them full size 10MP pictures...done it 3 times with full size and got poor quality...... next time i'll resize (regretting)

 

[RacePhoto]

i'm not sure if you alwys need exact 300 DPI image...but for sure with walmart.....if your image is 10MP and you want to print 4x6...better size it down before taking it for print.....they dotn come out nice fi you give them full size 10MP pictures...done it 3 times with full size and got poor quality...... next time i'll resize (regretting)

This sounds like an interesting experiment in the making.

You are saying that I'll get better prints by reducing the size of the image, before I take it in? Sounds counter intuitive? Why would I want to degrade an image, to make it better?

Type slow, I may have to read it more than once...

 

[markc]

Some printing hardware requires it. Some of them, like dye-subs, print one dot per pixels. For them, DPI and PPI are the same. If you send something bigger, it has to be shrunk to match, and their software may not do as good a job as you can do at home with Photoshop. Some require it for other reasons. It's good to find out exactly what the "native" resolution of these printers are, because for some it's 360 DPI or something other than 300 DPI. You can pick up finer detail if you get it just right.

Printers like inkjets and lasers use many dots to make up a single pixel. This is why you will see things like 2400 DPI and up. That may seem like a waste if your image is only 300 PPI, but it allows that one pixel to have its own dither pattern. You don't have to rely on just having the printer pick the closest color. Many colors can be blended in that small space. Dye-sub printers use a transparent dye, so they don't need to use a half-tone.

Basically, sending a print out has different requirements from printing at home (though they may be the same if the lab uses a large inkjet). It's good to find out what equipment is being used so you can adjust for it.

Here's a couple of links you might find interesting:
http://www.shortcourses.com/how/printers/photoprinters.htm
http://www.alpenglowimaging.com/resolution.htm

 

[MACollum]

i'm not sure if you alwys need exact 300 DPI image...but for sure with walmart.....if your image is 10MP and you want to print 4x6...better size it down before taking it for print.....they dotn come out nice fi you give them full size 10MP pictures...done it 3 times with full size and got poor quality...... next time i'll resize (regretting)

Maybe Walmart is doing their own resizing and screwing up the quality? I don't know how they do it but I know they will crop for you if the ratio is off, and their cropping software (or whatever they use to do it) will crop indiscriminately. My old Nikon Coolpix took pictures at 4.5 x 6 and I always had to crop before printing if I didn't want them messing up my pictures. This is another reason why I always crop my big picture files down to 1800 x 1200 (for a 4 x 6). I don't want them messing it up so I make sure they don't have to do any work other than printing (and they've screwed that up enough times anyway :x )