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-   -   180 ppp resolution from the camera (https://forums.steves-digicams.com/canon-21/180-ppp-resolution-camera-92763/)

genci Jun 17, 2006 7:14 AM

I´ve got a S45 for 3 years and today I´ve realized that images from the camera are 180 ppp resolution instead of the 72 ppp.

Could anybody give an explanation of this 'CSI' strange resolution?

Regards from Spain

JimC Jun 17, 2006 7:43 AM

It's just a number in the image header, and most software ignores it entirely.

The number of pixels per inch you have will depend on the print size.

For example, if you need 180 pixels per inch of detail at an 8x10" print size, you'd need to send the printer a 1440 x 1800 pixel image (approximately 2.6 Megapixels):

8 inches x 180 pixels per inch = 1440 pixels
10 inches x 180 pixels per inch = 1800 pixels

But, if you took that same 1440 x 1800 pixel image and printed it at 16 x 20 inches, you'd end up with only 90 pixels per inch of detail:

1440 / 16 inches = 90 pixels per inch
1800 / 20 inches = 90 pixels per inch

See my posts in this recent thread for more details:

http://www.stevesforums.com/forums/v...mp;forum_id=70


genci Jun 17, 2006 9:52 AM

Thanks JimC, but I think you have misundeerstood my question or perhaps I haven´t explain it allright.
What I mean is that when you get the image files from the camera they usually are at 72 dpi, but mine (from the S45) are 180 dpi photos and that is what I don´t understand.



JimC Jun 17, 2006 9:57 AM

I understood you.

What I'm trying to tell you is that it's only a number in the file header. It doesn't impact the actual image at all.

Some cameras put 72 in the header, some put 180; some do it differently depending on whether you're shooting raw or jpeg.

But, it's only a number that most software ignores anyway.

Here's an article that may help:

http://www.photo.co.nz/faq/resolution.htm


JockScott Jun 17, 2006 10:19 AM

JimC wrote:
Quote:

I understood you.

What I'm trying to tell you is that it's only a number in the file header. It doesn't impact the actual image at all.

Some cameras put 72 in the header, some put 180; some do it differently depending on whether you're shooting raw or jpeg.

But, it's only a number that most software ignores anyway.

Here's an article that may help:

http://www.photo.co.nz/faq/resolution.htm
Quote:

That link explains DPI and PPI well! Thanks


genci Jun 17, 2006 11:13 AM

Well, now everything is clear. Thanks again for your help, JimC.

ajaynejr Aug 6, 2006 8:01 AM

Pixels per inch or dots per inch is totally meaningless until you have an image size in mind (print size or even transparency size in the case of slides). Then you have to do the calculations yourself given the horizontal and vertical pixel count.

On a computer monitor or TV set, pixels per inch depends on the screen, not on the source material. For non-CRT screens the pixels per inch is fixed. For CRT screens the pixels per inch depends on the computer video card and on the operating system selections. The screen imposes some limitations. For detailed analysis of a photograph you want to zoom it on the screen to achieve a 1:1 pixel match between the source material and the screen (and also make sure the computer video card is delivering a 1:1 pixel match).






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