Sizing a picture to a specicific size and then add border

Hi all,

I am new to the DSLRs and the printing of high quality pictures. I am going thru a printing company and I need help in darktable for it to print to the specific size…

I can’t find what I need in darktable and I don’t know people who use it to get help. I even tried gimp to see if I could get it done there and I thought I did - but the picture is still too big.

The picture (the printed part) needs to be 13.125 in W x 10.1875 in height. Then on 3 sides I need .5 in border and the 4th needs to be .75 in. So the overall size, with border, will be like 13.875 x 11.43. I will then use a 12x18 size to order from the printing house.

Gimp had canvass size and border but it still printed (the actual picture) too big.

So I either some how effed up the GIMP processing or it was not the “correct” way to do what I need.

How can I do what I need with darktable v4.6?



GIMP should do this fine.
In the crop tool set the ratio of the cropping
Then you need to scale the image. Precision to four decimal places may not be possible.
Then you need to create a new layer filled with white.

Then just move the white layer to the bottom of the stack and position the image where you want it placed.

Doing this gets me to:

I finally got this but shouldn’t I be able to see the white border?


I guess it is the ratio that is off and GIMP is changing the print size:


I am not sure why the link icon is activated in the layers dialog. That is not needed. If you turn of the eyeball for the ducks layer you should see a solid white layer.

I am going to redo it today. I can see the white layer when I click on it but just expected to see the layer underneath as the border.

I had to change a calculation as one was slightly off.

After scaling the image, instead of creating a new layer, change the canvas size (Image → Canvas Size…). Turn off proportional resizing, add twice the frame width to the length and width of the canvas, click the center button, set the fill to white and click ok.

This weekend I am getting back to this… :slight_smile:

Three simple GIMP steps.

Make a new image ‘n’ px bigger than your target, say 32.

Fill the new image with whatever you like, say mid-gray.

‘Open as Layers’ your target. It centers automatically!

Export with no further ado:


I think I finally got it - I need to recheck measurements in GIMP before sending it off. I will have instructions to not print if, for some reason, the measurements were not correct.

I have to do inches - no idea how to convert inches to pixels…

I’m probably not understanding that.

You know your image size in pixels wide x pixels high. You know the required print size in inches - so the conversion factor is (pixels wide)/(print wide) px/in or ppi as it is often written. So, for 256 ppi, a 1/4" border thickness would be 64 px.

I know the required print size in inches… The way my brain works - staying in inches the entire time is FAR easier to conform rather than having to switch back and forth.

Unfortunately my app doesn’t allow me to express a border size in inches, or mm for that matter, AFAIK.

Dimensions can be specified in inches without converting to pixels.

But that only works correctly if you specify the correct conversion factor (resolution in ppi), which depends on the output device; printers are not all 300 ppi… So @CylonRed will have to contact his print shop to get that resolution (and if they cannot or will not provide it, I would change shop).

In both GIMP and darktable you can then set that resolution when specifying the size (canvas etc. in GIMP, export in dt).

I don’t print much and find it hard to understand the concept of having to specify the “resolution in ppi” in order to print an image. Is that not done by the print driver when you tell your app. the paper and margin sizes? I assume that we are not talking the x,y resolution tags in the EXIF.

I also find the concept of sizing a picture and then “adding a border” a bit confusing inasmuch as any picture for printing includes a border if so desired i.e. the border is not a separate item as far as the printer is concerned

I need a specific size border and it is different for the bottom from top/sides. So - it seems to me that specifying the border is the best thing to do - to make sure they are correct or the border is enough to be cut down to the correct sizes.

This is my first time going thru this process with a printer and editing photos and trying to get to a specific size. These are going up at my work and the boss wants a specific sizing/framing.

Which is why I did inches in GIMP.

Those numbers don’t add up.

If you have an image that is 13.125 x 10.1875 inches, and you add a border that is exactly 0.5 inches to all four sides, the final dimensions will be 14.125 x 11.1875 inches. You want one of the four borders to be more than 0.5 inches (which border?) but the final size should be only 13.875 inches wide, which is less than 14.125 inches.