Preview shows 72 dpi for a 300 dpi scanned image

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)

-g wrote:

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)

cnudi wrote"

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?

If you are seeing image dimension of 72x72 in the Finder (GetInfo) your image is only 72x72, which would explain why you see the same 72 in Preview.

In any event, the Finder shows the pixel dimensions of the image, not the resolution. A 4x6 photo scanned at 300 dpi would be 1200x1800 not 300x300.

Are you sure you are scanning at 300 dpi? What scanner & scanning app are you using?

1) Double check the Scanner Spec's and the Scan Settings.

2) Try using Image Capture instead of the Manufactures Scan-ware.

go to > Image Capture User Guide for Mac - Apple Support and select your macOS version.

+1 on trying Image Capture. I've never used the Epson scanning software that came with our ET-3850, only Image Capture from macOS 10.13 high Sierra through macOS Tahoe.. Zero issues with displayed resolution.

i want to CORRECT AN ERROR in my example:

it should read like this

EXAMPLE:

8000 x 6000 PIXEL DIMENSIONS

RESOLUTION at 4000 ppi (pixels per inch)

Document Size: 2" by 1.5"

is "identical" to the following:

(except for how RESOLUTION ppi is defined which in turn affects Document Size, length/width)

8000 x 6000 PIXEL DIMENSIONS

RESOLUTION at 72 ppi

Document Size: 111.111" by 83.333"

BOTH RESOLUTIONS sit on the drive at exactly 137.3MB (in 8-bit RGB)

for optimal scanner performance -- scan at your scanner's true OPTICAL RESOLUTION

you may need to dig for that spec

and ensure SIZE covers what you need -- i generally scan larger that I think I need

again, RESOLUTION is a weak measure (for reasons previously explained) -- the true measure of a pixel-based image is PIXEL DIMENSIONS

cnudi wrote:

I checked the GetInfo panel and my photo pixel dimensions are 1044x1044. I then looked at the photo in Apple Preview app and it says the photo, which I thought was 3.5x3.5 inches,

If your original image is 3.5” X 3.5” and the resultant scan is 1044 X 1044 pixels, it is being scanned at 300 DPI.

You have a 72 dpi image at a specific size.

I just split a single-page PDF into a 300 DPI PNG image. Here is what Preview 11.0 on Tahoe 26.2 shows for its Inspector of that resulting Letter-sized image:

You are welcome.

A little note about scanning: if you think you might need to print a larger version of the existing photo, it may be advisable to scan at a higher resolution, such as 600.