If you have the printer set to 'Borderless' the original size will be increased by the driver, unless you select 'Edit>Preferences>Print and Page Formatting>Borderless Overspray>Disable from the menu.

HTH

Brian

I assume you want to load an image into the queue in Qimage and want Original Size in PPI.
I also assume you know how to do it because you are only asking why sometimes it works and sometimes not.

Some file types, such as the PS PSD and the DNG files do not carry the Original Size with them.

But as Terry pointed out, WHY, Why Why, not just use Custom size and tell Qimage that you want a X.xx by Y,yy print size.?

Whatever it may be. Asking for a 10.57 x 14.89 print is more accurate than Original size no matter how odd the size may be that you want to print.

best.
Fred

One of Qimage's major features is that it does always re-size an image to a resolution equal to the native resolution of the printer: usually 720ppi for Epson, 600 ppi for Canon & HP. This prevents the driver doing it instead. The interpolation algorithm used by Qimage is world class: the best that is why prints from it are good. If you do happen to have re-sized in another program, you have already degraded the image.
I can only say again, use Qimage to its full potential, forget what PS & similar have to do to size an image and make life easy for yourself.
I suspect that is because the embedded size data in the image is in imperial - we always talk about ppi not pixels per cm.
Terry

I know it isn't etiquette to pop in like this, but.... sir, you are laboring under a false premise.
There is no PPI until you decide on a print size.   That's what the "i" is in PPI. 
PS starts you out with a made up print size in order to show some starting point of ppi.
It has no value or use other than to make a false comfort zone for the user.
Years ago, PS started all images out at 72 PPI. If you went to make a print, it would make a 40 inch long print.
Lately, they changed that default to 180 ppi.   
It means nothing until you decide on a print size.
As you point out, your image has a native size... but digital images have a size measured in pixels in a horizontal plane and pixels in a vertical plane.  There are no inches or cm involved here at all.

The ppi will be determined by the print size....  Example: If your pixel width was 4000 pixels, and the print size YOU CHOSE was 10" wide, the PPI would be 400ppi.

Next item that Terry pointed out. The power and strength of Qimage is to interpolate to the input dimensions of you printer. An Epson is typically 720 ppi or 360 ppi.
Qimage takes your image that is ready to print and sends that image to the printer at the perfect ppi so the printer driver wont manipulate it again.
Why is that good?
The more times you reorganize pixels, the more you degrade quality.
So if you try to make (example) 300ppi when creating your image in PS and Qimage has to change that anyway to 360 or 720, you didn't help yourself!

To sum up, any image I open in Irfanview, I can check, and in  the EXIF, there is no PPI. Some images show a DPI and most often that is blank.

Perhaps, this will help.   Let us mentally scan an image into the computer from our scanner. It's an old 5 x 7 of grandma.
Before we scan it in, we set the DPI/PPI to a number so we can get better resolution on the scan.  In a scan, DPI and PPI are the same at this moment.
We choose 300.... what will the resolution of the scan be? 1500 x 2100
If we chose 600 for the DPI/PPI, the resolution of the scan would be 3000 x 4200.

Now we want to print the scanned image.  PPI is no longer at 300 unless you want to make a 5 x 7.   If you wanted to make wallet size, 2.5 x 3.5, the ppi would be 600.
If you wanted to print a 10 x 14, the ppi would be 150.

Now let's get back to you!
If you told Qimage to bring that scanned image into the queue at it's "ORIGINAL" size, it would come in at 300 ppi and the print would be set at 5 x 7 using the arithmetic from above.
But what was the point?
All you had to do was ignore the original size selection and just tell Qimage to make a 5 x 7 print. Same result less work, less confusion.... and when you measured grandmas old frame, it was larger. It was 6 x 9.
Just tell Qimage, I want to make a 6 x 9 print. PPI goes to 233 ppi.

So what is Original size used for?
Printing a Target image where the size of the print must be exact at a specified PPI.

Use PS to make your image just the way you like it.... layers and more layers, and when done, save as a PSD or a TIF or a JPG. Open that in Qimage, and select a print size, and print!
Easy Peasy.

Fred

No one ever said that.
What we all said was, you have an image with resolution but no Pixels per inch until you are ready to print and have decided on a size print.

OK Old Fox.
You wore me out.
Maybe someone else can make it clearer, that is, if you want it to be clearer!

Best,
Fred