Philipschmitten Loc: Texas

I am currently shooting at the fine setting on my Canon XSi and it is really a large file when trying to email. How much resolution is really needed for, let's say up to 11 x 14?

JimH Loc: Western South Jersey, USA

You can reduce the FILE SIZE without reducing the RESOLUTION.

To print 11x14 at a minimum of 150 DPI you would need a file at least 1650 x 2100 pixels in size, which works out to around 3.5MB in size.

Physical size, print size, resolution, and DPI are all related, but not interconnected.

rpavich Loc: West Virginia

What software are you using for post processing?

mrbailey47 Loc: Tempe, AZ

For some reason I seem to grasp just about everything else easily about the computer side of photography but keep drawing a blank when the topics you mentioned come up, I.E., size, resolution, dpi and so on. When a contest asks for files to be submitted at 300 dpi or "no larger than "x by y pixels", how and where do you do that? Is there any one source that spells all of this out? Thanks.

rpavich Loc: West Virginia

Here is a good link that explains it

http://www.rideau-info.com/photos/mythdpi.html

JimH Loc: Western South Jersey, USA

You are not alone, and it's not your fault. Forces with a vested interest in keeping consumers confused perpetuate the madness.

The difference stems from the fact that viewing on a computer screen and printing on paper use two different methods of determining output quality.

For all intents and purposes, consumer level computer monitors display at 72 dots per inch. So no matter what "DPI" or "PPI" your image is, if it's greater than 72, you WON'T NOTICE IT ON SCREEN.

For all intents and purposes, consumer level ink-jet printers print at 150 or 300 dots per inch. If you see a printer advertised as "1200DPI", they're scamming you - they add together the four 300 DPI's of cyan,magenta,yellow and black ink. Tricky, eh?

If you know the "DPI" of your image, you can tell how large you can print it without suffering image quality loss.

A 5x7 sheet of photo paper can print 5 inches times 300 DPI or...right, 1500 pixels in that dimension. The seven inch side can handle 7 times 300..... anyone? Bueller?... right, 2100 pixels.

So a 1500 x 2100 pixel image can print perfectly well on 5x7 paper. And takes up....anyone?... 1500x2100 = a little over 3mb.

So - a 3mb digital image will print perfectly at 300DPI on 5x7 paper, and...guess what?...pretty darn good at 150 DPI on...do the math ( 5*2 = 10, 7*2 = 14), 10x14 paper, which we don't use, so call it 9x14.

BUT, if you reduce your images to 72 DPI, as many "Save for the web" functions do, they will probably print horribly at any but very small size. So don't do it.

Try not to get flummoxed by all the BS about DPI, PPI, pixels, and everything.

mrbailey47 Loc: Tempe, AZ

Thanks, JimH. This was very helpful ... maybe I just worry too much. Anyway it seems needlessly complex.

mrbailey47 Loc: Tempe, AZ

Thanks, rpavich. This site is VERY helpful and as soon as I get back from this road trip I'm on I will study it in more detail.

Elle Loc: Long Island, NY

[quote=JimHquote]

Excellent explanation of the differences Jim. I know them but you spelled it out.

commodore-don Loc: Cleveland, OH

Jim's excellent explanation above was pretty correct except for one thing. The "original VGA" 640 X 480 pixel monitors had a screen resolution of 72 pixels per inch. As monitors got higher resolutions, super VGA at 800 X 600 PPI and 1024 X 768. resolution became about 96 pixels per inch on just about all. If you size a photo to say 6 X 4 inches at 72 PPI resolution and actually measure it on your monitor screen, you will find that it measures less than 6 X 4 inches unless you happen to be using an old VGA monitor. I doubt there are many around anymore. The larger LCD monitors such as the 1920 X 1200 pixel of the calibrated monitor on which I edit my photos in Photoshop CS5 actually has a screen resolution of 124 pixels per inch.

I never overwrite the out-of-camera original pictures, so I often have numerous versions of the same photo done at different resolutions. I use the crop tools in PS to downsize the high-resolution originals for viewing on a monitor or in an email. I have preset various crop sizes to accommodate this: for example, going back to that 6 X 4 inch example above, it would have been created with one swipe of the crop tool set to 6 X 4 inches at 96 PPI. Actually, this is NOT cropping the picture as the entire picture is swiped, but is reducing its pixel count from the original 715 PPI to 96 PPI. I then save the cropped and re-sized picture with a different file name, including the size and resolution, then close the original from which it was created. For example, the original might be DSC_0010.jpg. After editing it to a final version at the original resolution, it would be saved as DSC_0010F.jpg, an 11 X 14 cropped version for printing would be DSC_0010-11X14@300ppi.jpg and an internet version would be DSC_0010S.jpg. The "s" designation means small size, or 96 PPI version.

In my opinion, Photoshop does a very good job of interpolation when downsizing an image to screen resolutions for use on the Internet or in email. When going larger than the original pixels for prints, and because I insist on never going less than 300 Pixels Per Inch resolution in prints, I have used Genuine Fractals and now OnOne Software's Perfect Resize for many years. It does a super job.

JimH Loc: Western South Jersey, USA

The Commodore is on the money re: VGA vs XGA vs newer LCDs. I didn't want to confuse things even further but he's exactly correct - most NEW monitors, especially LCDs, are much better than the old CRT VGA displays..

Anyone for CGA? Eight Glorious Colors in 40 columns.... :)

Dria Loc: Ohio

JIM--I am printing out and saving your dpi etc answer-- that is one of those things I know but explaining it---ugh!