Question on Resolution Sizes in PSCS . . .

[RJSorensen]

I have Photoshop CS and have been using Canon G2, G3, G5, Pro1 cameras up until recently, when I purchased a 20D. I use the Mac version of PS, in case that makes any difference in the answer.

In Photoshop>Image>Image Size my 20D gives me a resolution of 72 pixels/inch. All of my Canon G's would report 180 pixels/inch in this box. Of course the 'raw' size is like 48 inches in width and etc.

So what is the difference . . . and does it affect my print quality? Has anyone else seen this? Excuse me if this is old hat and or old news but sometimes you have to ask. This seems to be a wonderful place to do so.

My thanks to those whom are able to assist with this.

[Chazs]

I'm curious, in the Metadata tab in file browser, does it show a resolution of 180 or 72? My DRebel shows 180.

[RJSorensen]

I just checked as you asked Chazs, and in a group shot today, mixed Pro1 and 20D's, the Pro1 are 180 and the 20D's are 72.

This just don't seem right, I am trying to shoot in jpg & highest res that I can, why shoot low? Anyone have an answer or a clue to work on?

[tim]

It makes no difference what it says in that box unless you go to print something. Even then it can make no difference depending what you tell the printer. You have a number of pixels in your picture, the PPI setting just tells it how long to make the scale/ruler.

Edit - if you resize and want to keep the detail the same but want to change the ruler you have to turn off the "resample picture" check box.

[Jesper]

This is one of those frequently asked questions....

The resolution number (expressed in Dots Per Inch (DPI) or Pixels Per Inch (PPI)) does not tell you anything about the quality of the image.

The only thing that matters is the size of the image in pixels. For the 20D, at the highest quality setting, the image will be 3504 x 2336 = 8.2 megapixels.

A digital image is just a rectangular matrix of pixels inside the computer's memory. It doesn't have a physical size in inches. But if you want to display it on a monitor, or print it on a printer, the image will be printed with certain physical dimensions.

The PPI or DPI setting is a "hint" that tells Photoshop how large the image should be displayed or printed. If you print a 3504 x 2336 pixel image on a piece of paper of 12 by 8 inches, the print will have a resolution of 3504 / 12 = 292 (or 2336 / 8 = 292) pixels per inch.

You can change the size at which an image is printed in Photoshop without changing the image itself by choosing Image / Image Size and UNchecking the "Resample Image" checkbox, and entering a different size in inches or a different DPI number.

[RJSorensen]

Thank you Tim and Jasper . . . I will try to mull this over and work on being able to understand it. The resample check box, I have never used this and was thus unaware of its use and or changes to the photograph size/resize.

This hobby is something that I do so enjoy . . . but having a computer and a camera does not make me either a rocket scientist nor Charles . . . if you know what I mean. I am just a poor farmer out in the sticks.

My thanks again to those whom replied.

[mphoto]

For a good explanation of PPI and DPI and their relationship to printing see:
http://www.nikonians.org/html/resources/guides/resolution_and_prints/resolution_and_print_size_1.html