Are both images ok for high quality print?

[marygb]

I have two images of basically the same subject. One shows 300dpi but is smaller while the other shows 72dpi but is much larger. Can I change the one that is 72dpi without re-sampling and use that? I get a lot of photos from family that have settings like this - 72dpi but very large and I need to know if they will print well.

Attached is snapshot of photos along with the one of the actual photos - the other one is too large.

[Geoff F]

What really matters, Mary, is the total number of pixels. Resolution just 'converts pixels into actual printable sizes'.

Both of those images actually have around 10 ins at 300 ppi (3,000 pixels). The pixels appear to give different sized images simply because of the different resolution.

But I don't quite understand the width of the right hand image. I assume it should be 1,752 pixels. I appear to be seeing another number after that and it can't be 17,521 pixels can it!

So just divide (or multiply) the number of pixels by the resolution to give the actual image size when printed.

Incidentally, some printing shops insist on having 300 ppi but in reality you can usually print at a much lower resolution without any noticeable difference. In fact, in many cases it is impossible to tell the difference between prints at 200 and 300 ppi.

ps. some cameras and software automatically default their settings to a resolution of 72 ppi while others use a different resolution. Which is why there can be so much apparent confusion.

[marygb]

Thanks for the explanation. The 2nd image was 1752x2829 - what you saw that looked like a 1 at the end was my cursor.

So now I know I can see how 2048/300 = 6.827 and 1752/72 = 24.333

I just took the 2nd image and changed the resolution to 300 and un-checked resample image options and printed both images which are near exact to each other.

One last question - when you say that both images have around 10 ins at 300ppi or 3,000 pixels, how do you get that calculation?

Thanks so much.
Mary

[Colin Southern]

One last question - when you say that both images have around 10 ins at 300ppi or 3,000 pixels, how do you get that calculation?

Because both are around 3000 pixels high. Don't assume that you NEED 300 PPI though; whilst it's true that that's what's used by high-end glossy magazines, 180 PPI is STILL over 50 tone changes per square millimeter, which most folks couldn't resolve without a magnifying glass.

Also - the bigger the print - the greater the viewing distance - and the less the eye can resolve. For that reason, you could print these pretty much any size you like and - from a normal viewing distance - they'd still look just fine (I do it all the time).

Often people will ask "how big can I print this image" where as in reality, the question should be "for a given print size, what's the minimum viewing distance for this image". I've printed images that contained only about 1% of the ideal about of information (the camera was set on VGA resolution (640 x 480 pixels - AND - we had to crop it to about 1/2 that!) - then I had to print it at about 22 x 15 inches. How did it look? Up close, bloody awful - from about 6 or 7 feet away, just fine.

[Geoff F]

Just basic maths, Mary. 3,000 (pixels) divided by 300 (pixels per inch) = 10 inches.

So simple, even I can do it.

It is exactly the same principle as the figures you stated 2048 pixels divided by 300 ppi gives 6.83 inches.

And working it the other way. How many pixels do I require for a print which would be 10 ins long at 300 ppi? 10 (inches) x 300 (ppi) = 3,000 pixels needed.