Printing quality paremeters enquiry

As long as the pixel count doesn't change, the resolution is just an image "tag", an hint to compute the "physical" size at that resolution. So 5472 x 3648 at 72ppi or 300ppi is the same image in a file, until you print it at a given resolution, that can be different from whatever is set in the file.

Usually the print resolution is selected taking into account the printing technology, print size, viewing distance, and pixels count of the original image, and the image resampled accordingly. Downsampling is usually OK, upsampling usually introduce issues, but for smaller values. Thereby the more the native pixels, the larger the image can be printed at higher resolutions - and thereby viewed closer. There are formulas available, which take into account the human eye resolution.

72 ppi is usually too low, but for larger images seen far away. Most inkjets prints are printed at around 300/360ppi, some higher res one at 600/720 (Canon/Epson native resolutions), some larger ones may use lower resolution (240, 150, as needed). Image printed using different technologies may use other values.

For that reason, the resampling is usually made by the print process itself, when all the needed parameters are known. If you know them exactly in advance, you may perform all the steps yourself (if really needed for specific reasons), otherwise you may make a resample and your customer another - and it will just mean a degraded quality.

Thereby, give your customers an image with a pixel size large enough for their print size without upsampling, the image file resolution is not important.

LDS is correct that if the pixel count remains the same, then it is irrelevant what the dpi says. Pixel count is the true file size. I worked at a small pro lab for two decades and continue to have my stuff printed by them. Print resolution is 300 dpi (or ppi - those terms are used interchangeably). Ideally your file should be 300 dpi at the size you want printed. If you change the dpi from 72 to 300 and keep the same pixel count and the new (smaller) image size in inches is as big as they want to print, you are done.

If I need to upsize a file for printing I do it in Photoshop Elements (the program I have at home). Though I was not a printer or technician at the lab, I can testify this gives me good results. I open the image in Elements and first change the dpi to 300 and then put the pixel count back down to what it was originally. Then I increase the size a few inches at a time until I get to the desired final print size.

If I think I am pushing how big I can go, I will take this new file with the ruler showing on the screen and crop out an 8x10 inch section. Then I have the lab do a cheap 8x10 print to see how it will print at the final large size.

Use 240-360 ppi based on what yoour printer is.

DPI is not the same as PPI, but some people mistakenly use them interchangably. DPI is a printer term meaning the number of dots per inch, but it takes several dots to produce a pixel.

Read more?

https://99designs.com/blog/tips/ppi-vs-dpi-whats-the-difference/