1200 DPI Scan Integrity

[scottjoyce1234]

Hello,

I am editing a 1200 DPI 24 bit scan using the "Divide Scanned Images" script.  It is a scan of a stamp album page and when I run the script, it finds all of the individual stamps on the page, divides (crops/cuts) them out and saves each individually to a JPEG file.

My problem is that it is saving all of the individual stamp images as 600 DPI so I am losing 1/2 of my granularity.

I went into the script and found where it was saving the files as 600x600 and changed it to 1200x1200;However, it really isn't maintaining the integrity of the original 1200 DPI scan.

Does anyone know how to be able to maintain the 1200 DPI integrity?

Thanks,
Scott

[Blighty]

The thing to understand is that a digital image only has a size in pixels.

Lets say you scan a 10"x8" page @ 1200 dpi
Your image is (10x1200)x(8x1200) pixels
=12000x9600 pixels
The image now has size in pixels only, the dpi is irrelevant.
Gimp can a store a dpi value, but it is dormant until you print on paper.

If a stamp is 1" x 1.5" in size, once scanned it will have a size of
(1x1200) x (1.5x1200) pixels
=1200x1800 pixels.
Check the the size of a stamp in pixels.
If it conforms to the above everything is OK
(and the stored dpi is just a dormant value and won't affect anything.

NOTE:
1200dpi is a very high value for a stamp. It is very unlikely that any stamp has a resolution any where near that.

[scottjoyce1234]

(07-26-2018, 04:04 PM)Blighty Wrote: The thing to understand is that a digital image only has a size in pixels.

Lets say you scan a 10"x8" page @ 1200 dpi
Your image is (10x1200)x(8x1200) pixels
=12000x9600 pixels
The image now has size in pixels only, the dpi is irrelevant.
Gimp can a store a dpi value, but it is dormant until you print on paper.

If a stamp is 1" x 1.5" in size, once scanned it will have a size of
(1x1200) x (1.5x1200) pixels
=1200x1800 pixels.
Check the the size of a stamp in pixels.
If it conforms to the above everything is OK
(and the stored dpi is just a dormant value and won't affect anything.

NOTE:
1200dpi is a very high value for a stamp. It is very unlikely that any stamp has a resolution any where near that.

10-4...Roger Wilco...Thanks!

[rich2005]

Some pictures to go with that.

I was just looking at DivideScannedImages the other day, surprised that it still works in Gimp 2.10.4 (at least it does here)

The print resolution as reported in Gimp is not the same as the scan resolution. Once an image is scanned it has a definite size in pixels. The print resolution is then only if the image is printed.

This is a tif scanned at 1200 ppi. In Gimp the print size is shown as 1200 ppi. Measuring one of the stamps gives a size in pixels of around 1460 pix (a bit skewed)



It looks like you are using the batch option, that is where the 600 ppi line is in the script. I do not know why 1200 does not work.

Scan is divided, (and deskewed) The print size does show 600 ppi but the size of the object is correct, round about the 1460-ish mark. You have not lost any definition only an internal image setting.



If you need to re-set the ppi to 1200 then need to find some script that changes the setting. Not Gimp but ImageMagick

Code:

mogrify -units pixelsperinch -density 1200 *.png

sets the print resolution to 1200 for a folder full of png images.

[scottjoyce1234]

Thanks...I also found that the "deskew" option was written to output a maximum of 600 DPI so if I don't use that option, it saves the images as 1200 DPI.