I'm scanning in hard copy photos at 300 dpi, but when I view them in Preview the resolution shows 72 dpi. Also in the document information in Finder it shows the resolution as 72x72. Shouldn't it show 300 in Preview and 300x300 in the file information in Finder?
[Re-Titled by Moderator]
Original Title: Resolution dpi confusion
iMac (M1, 2021)
PIXEL DIMENSIONS are the numbers that matter in scanned images (and digital photographs and pixel based graphics) -- not RESOLUTION
try opening the pixel image in Adobe Photoshop, then Image> Image Size
note: Pixel Dimensions -- and Document Size, Resolution
EXAMPLE:
8000 x 6000 pixel dimensions
at 4000 ppi (pixels per inch)
Document size: 2" by 1.5"
is the same as
8000 x 6000 ppi
at 72 ppi
Document size: 111.111" by 83.333"
BOTH RESOLUTIONS sit on the drive at exactly 137.3MB (in 8-bit RGB)
in fact, this type of edit is the only move you can make in Photoshop that doesn't degrade the image
"You move in Photoshop -- You Lose"
+++++
72 ppi (pixels per inch) is a common screen resolution
apparently that is what Apple's Preview.app uses (though i don't use Preview app)
i would speculate Preview otherwise maintains original pixel dimensions
300 ppi is a common resolution used for printing
I once sent a designer a scan i did at 4000ppi -- the optical resolution of my Nikon film scanner
he emailed me in frustration my scan was the size of a postage stamp!
yet it sat on the hard drive at over 250MB (16-bit RGB)
and had 8000 pixels wide (Pixel Dimension)
to his credit -- he got it instantly when I pointed that out -- and he was able to adjust my Document Size to his layout with minimal loss in pixel quality...
+++++
dpi (dots per inch) are easily confused with ppi -- dpi is more related to printing terminology -- how many dots your printer is laying down per inch (in oversimplified terms)
Thank you for your advice and help.
Preview shows 72 dpi for a 300 dpi scanned image
