resolution

[maldon_walker]

I have both a 1D-MkII and a 20D. (I am retired, with too much money

and no brains....so my kids tell me). Photoshop Elements 3 tells me

the resolution for both cameras is 72 vertical and 72 horizontal. Is

this pixels per inch (as I suspect) or something else. And why 72.

I've trawled throgh lots of sites including Canon's, but can't find

any references.I hope I am not being a pest, but it'll worry me

unless I understand.

[bobatkins]

It's the print resolution and it's set to 72ppi for historical reasons which currently make no sense. At one time monitors were something like 72ppi.

 

You can change it to anything you want. Most people think that 240 to 300 ppi gives the best print quality.

[awindsor]

This is a meaningless default. It dates from years ago when this was (apparently) the standard pixel pitch on monitors (there is at least one old Apple model with a 72 PPI monitor). It doesn't mean anything and is not used for anything.

[bobatkins]

Actually the ppi setting is used in determining print size.

[phule]

In Photoshop, when you set the resolution to 300 or 240 or whatever, make sure you un-check Resample Image.

[kelly_flanigan1]

72 is WAY closer to the average JOE's monitor resolution than 300; in every nook of the woods. 72 might also be a good guess for a kids weight too; not 300. Yes there are folks still running VGA 480x640 on the internet; and here we have some at 600x800.

[kelly_flanigan1]

The settings are determined by the monitor size; how the with setting is adjusted; what resolution one is running at. Here we have 5, 9, 14,15, 17, 19, and 21 inch monitors; each run at maybe 5 different resolutions. Each image of say 240x320 pixels will be a different size in inches on the different screens in usage. Each will have a different scale; or pixels per inch on the monitors screen. The 72 number is just a dart; a rough old average; like saying most cars get 24 mpg.

[bobatkins]

Of course it doesn't matter about the screen resolution anyway. On 99% of computer systems you see EXACTLY the same image at EXACTLY the same size no matter what the ppi setting is, whether it's 1 or 1000, 72 or 300.

[press_photog]

The camera creates pixels in the X and Y directions, dependent on what you have set in the camera. My 10D shoots at 3072 x 2048 pixels, but I can set a smaller resolution if I want. There is no dpi set in camera, dpi is dependent on the output, be it a print or a computer screen. Whan you open a file in Photoshop, or whatever software you have, the pixels don't change, my image is still 3072 x 2048. What you OUTPUT to a printer or file is another matter. If I print a 4 x 6 from my original file, I would be printing at 512 dpi x 512 dpi, or 3072/6 x 2048/4. So think of the camera resolution in pixels, and the output to be the number of dots per inch which is dependent on the print or monitor size. If you don't have enough pixels for a given print size, Photoshop (and other programs) can "upres" your image by interpolation. Monitors display approx 75 dpi, so my file would be huge on such a screen. To see my file on a given screen size, say 1024 x 768, the pixels in the image would need to be 1024 x 7068 or smaller, and so on.

[robin_sibson1]

The purpose of the dpi setting on the PC, together with the option to choose different system font sizes, is to allow the system to make objects on screen a sensible size in relation to the display size and resolution. If you run a 19" monitor at 1600 by 1200, you are not going to find it easy to see screen furniture at 72dpi with small fonts! Conventional dpi choices are 72, 96, and 120. As Bob points out, the legacy value of 72 has no relevance to the usual usage in image files, which is to convert size in pixels to size in inches (so ppi rather than dpi). At one time there was a theory that ppi should divide printer dpi exactly (so, 300ppi or 240ppi with a 1200dpi printer, 240ppi but not 300ppi with a 1440dpi printer) to avoid banding effects, but this no longer seems to be much of an issue with modern printers.

[maldon_walker]

I find it hard to believe what I've just read. The question above was the first I've ever lodged in a forum of any kind. And I am astonished. In a world gone mad, there are still people out there, like you guys, who'll help an ole feller like me for no good reason other than the perceived need. My sincere thanks to all of you.