Are 72 dpi and 300 dpi images with the same resolution the same quality? [duplicate]

Question

I have a lot of travel photos I was hoping to sell as downloadable prints on Etsy but do not know how the whole dpi thing works. When I click on the properties of my picture on my computer it says 4608 X 3456/72 dpi. Now other prints for sale on Etsy say 300 dpi. Does that mean mine are not of high enough resolution. I have enlarged one of the photos and it looked really good. Do I need to put it into a photo editing software program to change the dpi if I want to sell it. Is there a converter somewhere to figure how big I can enlarge a photo to where it will still look good? Sorry so many questions.

Answer 1

The reason you, and everybody, have trouble figuring this out is because there is no such thing as the dpi of digital images. Images only have pixel dimensions and image quality. You can only get the dpi or resolution of the display of the image, not from the image file itself.

Only displays have dpi. DPI is how you define displays. For example, the display on a newer big phone has around twice as many pixels as an HD tv. Phones have a far higher pixel density or pixels per inch so images are displayed at a far higher dpi.

72 dpi is the old number used in digital. I think it used to be close to the resolution of old crt monitors.

300 dpi is the old standard for print. I was never in print so I'm not sure where the number came from but it's a print dpi. It's the dpi of the printout.

Answer 2

The size of your image is the 4608 X 3456 pixels, which is also basically the actual resolution created in the pixels.

It probably only says 72 dpi if you saved it in Adobe menu "Save For Web", which eliminates the Exif, which is where the JPG DPI number is stored (video monitors have no use for dpi). Then when no dpi is specified, Adobe just chooses to say it is 72 dpi, which has no meaning (and it is blank).

If you actually printed it at 72 dpi, it would try to print 4608/72 = 64 inches and 3456/72 = 48 inches, or 5.33 x 4 feet. That is not realistic, and 72 dpi is insufficient printing resolution.

Or at 300 dpi, it would print 4608/300 = 15.36 inches by 3456/300 = 11.52 inches. It would seem a good idea to show that it is that large. Since there will be other people that don't understand dpi, to sell it, it probably is a wise idea to change it say 300 dpi. But the size of the image is 4608x3456 pixels.

You can change the number to be 300 dpi or whatever you want it to say. To change it, UNCHECK the Resample Image box in the Adobe Image - Image Size box (so that it will not resample the pixels), and then when changing the Dpi number, the pixel count will not change (just the printed size in inches or mm will change).

If you use the menu "Save As" JPG, it retains the Exif, and keeps the DPI that you just changed (Save For Web would discard it again). If the first Save you did was "Save As" JPG, then it would have kept the dpi that the camera stored there (which also has no meaning, since the camera does not know how you will print it).

If you do not change the pixels in any way, it remains exactly the same image (same 4608x3456 pixels). The dpi number is simply an instruction about what size to print it (spacing the pixels to cover 300 per inch, or whatever), which you set at the time you print. Often when we print, we simply specify the paper size, and printing computes the necessary dpi number. The person printing probably will also have to crop it to shape for printing, because 4:3 aspect ratio paper is pretty rare.