What size are your digital files?

My "high-res" are 3600 pixels on the long edge, and my "web res" are 1200 pixels on the long edge, usually 85% quality in Lightroom.

So if I make high res images available that are 3600px on long edge, 300dpi and 100% quality (Lightroom settings) what would be the largest good quality print that could be made?

daystar wrote in post #18197604
So if I make high res images available that are 3600px on long edge, 300dpi and 100% quality (Lightroom settings) what would be the largest good quality print that could be made?

3600pixels divided by 300ppi = 12 inches, long side

However if you printed the same 3600pixel image at 240ppi the print would be 15 inches on long side (3600/240)
I doubt many people could see any difference in print quality.

If you printed it at 200ppi (and a LOT of people would find the quality more than acceptable), the print would be 3600/200 = 18inches on the long side.

Remember larger images are normally viewed from further away so the effect of using a lower printing resolution may not be noticeable.

Printing at 180ppi would result in this 3600pixel image printing out to 20 inches on the long side. Now a 20 inch image is going to viewed from further away than a 10x8.
Again a LOT of people will be satisfied with the result.

At some point, you will need to decide if
1) you can notice any degradation in image quality at the lower printing resolution
2) the degradation acceptable at that printing resolution.

You can get wonderful prints from printing at resolutions lower than 300ppi - but at some point the loss of quality will be both noticeable and unacceptable.
For me that is around 200ppi - I don't like going lower even though I know you can still get pretty good prints at lower resolutions.

Just remember, the printing resolution (ppi) is totally irrelevant UNTIL you actually do a print.
The two critical factors that affect quality of a JPEG image are:
1) the number of pixels in the image (eg 3600px x 2400px ... versus ... 1200px x 800px) and ...
2) the quality of those pixels (compression or quality level that an image is saved at)

AceCo55 wrote in post #18197677
3600pixels divided by 300ppi = 12 inches, long side

However if you printed the same 3600pixel image at 240ppi the print would be 15 inches on long side (3600/240)
I doubt many people could see any difference in print quality.

If you printed it at 200ppi (and a LOT of people would find the quality more than acceptable), the print would be 3600/200 = 18inches on the long side.

Remember larger images are normally viewed from further away so the effect of using a lower printing resolution may not be noticeable.

Printing at 180ppi would result in this 3600pixel image printing out to 20 inches on the long side. Now a 20 inch image is going to viewed from further away than a 10x8.
Again a LOT of people will be satisfied with the result.

At some point, you will need to decide if
1) you can notice any degradation in image quality at the lower printing resolution
2) the degradation acceptable at that printing resolution.

You can get wonderful prints from printing at resolutions lower than 300ppi - but at some point the loss of quality will be both noticeable and unacceptable.
For me that is around 200ppi - I don't like going lower even though I know you can still get pretty good prints at lower resolutions.

Just remember, the printing resolution (ppi) is totally irrelevant UNTIL you actually do a print.
The two critical factors that affect quality of a JPEG image are:
1) the number of pixels in the image (eg 3600px x 2400px ... versus ... 1200px x 800px) and ...
2) the quality of those pixels (compression or quality level that an image is saved at)

Thank you! I appreciate your detailed explanation. Very helpful! So if I lower the ppi, I can get a larger print that to the average eye won't be unpleasant. Did I understand this correctly?

daystar wrote in post #18197685
Thank you! I appreciate your detailed explanation. Very helpful! So if I lower the ppi, I can get a larger print that to the average eye won't be unpleasant. Did I understand this correctly?

Essentially yes ... BUT ONLY UP TO A POINT.

If you lowering the printing resolution too low, you will see a deterioration and it will be unpleasant.

As I say, I'm comfortable going down to 200ppi print resolution and at times I have gone to 180ppi
I can see the quality suffer there but it may or may not be acceptable to others.

You might want to conduct a few tests and see where it becomes unacceptable for you and your purpose.
That's what I did when I decided to agree to people buying photos off me.

Very best

Personally I think that for the majority of non photographers they are actually very likely to be more than very happy with prints done at 100 PPI. Lets face it people were generally quite happy with the quality of Kodak Disk film, which made the 110 negative look large, and a digital print at 100 PPI will be much better than that. Sometimes as photographers I think that we forget that the vast majority of people just cannot see the difference between what we would call acceptable, and stuff that we would delete without a seconds consideration quality wise.

Alan

daystar wrote in post #18197604
So if I make high res images available that are 3600px on long edge, 300dpi and 100% quality (Lightroom settings) what would be the largest good quality print that could be made?

What medium are you printing on, and what is the recommended PPI for that medium?

Three things of note:
First: PPI is just a derived calculation, pixels per inch. By itself, it's meaningless. The PPI (or DPI*) tag embedded in the image is meaningless.
There are two things that are real: Number of pixels, and number of inches. How many pixels are in the file? How many inches wide is the sheet of paper on which you're printing?
If you print a 3600x2400-pixel file on a 12x8 piece of paper, you printed at 300ppi, regardless of what the metadata in the file says about the PPI. If you print that same file on a 36x24 poster, you printed at 100ppi, regardless of what the metadata in the file says.

PPI only becomes important when you know the size of the physical print that you want, and you know what PPI is appropriate for that print medium. Use those two things to calculate the pixel dimensions of the file you export from Lightroom. If you want a canvas print that's 20x30, and the canvas printer recommends 150ppi, then you do a little math to figure out that you need a file that's 3000x4500 pixels.

Second: As alluded to above, the DPI tag in the metadata is all but meaningless. In a digital file, pixels are the only thing. A file exported at 3600x2400 pixels and 72dpi will be identical to a file exported at 3600x2400 pixels and 300dpi, or 10000 dpi or whatever. The pixels don't change.
(okay, little caveat: there are rumors that lightroom handles the export sharpening slightly differently depending on what you put in this field, but for this purpose the difference is not meaningful, I haven't personally tested it)


Third: Many people (including Adobe) use PPI and DPI interchangeably. This is technically not correct, they're not the same thing. PPI (pixels per inch) is the number of pixels from the image that will be rendered onto an inch of paper. DPI (dots per inch) is the number of ink droplets that the printer will physically deposit onto the paper - usually this is an order of magnitude higher than PPI. However, until Adobe stops using these interchangeably, the community at large won't be able to get our semantics straightened out.