Printing a scale drawing from a Photo

[rovingpaddy]

I had a search around but couldn't find any conclusive answers to what I'm trying to do. I'm new to the forum, so any help is very much appreciated. 

So, I need to produce patterns for making bicycle frame bags for my work. However not everyone lives local enough to do a physical drawing/pattern. So customers will email me a high res photo of their bike frame with a tape measure or ruler attached to the frame for scale.
My question is, how can I take this image from the customer and then using GIMP, make sure the image is at 1:1 scale and then print it out on multiple A4 pages? Is there even a way?

I'm very new to using GIMP so I'm completely lost at the moment.

If you can point me in the direction of any other topics or videos that may help that would also be great.



Cheers
Patrick

[rich2005]

The first thing is a measurement on the photo using the Gimp measure tool. Choose say 10 cm on the tape-measure (20 to 30 here) and determine the length in pixels. That value is shown bottom of the Gimp window.

Apologies for quality, these are photos rather than screen shots, I need to hang an actual ruler over the monitor.  Painted in a bit of green and the red is where the measure tool spans. 228.1 pixels  Go into Image -> Print Size and see what you have 

   

The X and Y resolution here are 72 pixels-per-inch (PPI) but might be anything depending on the camera.

Now get your calculator out and 10 cm = 228 pixels so 1 cm = 22.8  Change the units to pixels/cm and enter 22.8 in the X / Y resolutions.  By default Gimp maps the image in 1 pixel = 1 screen pixel but to see the image as it will print go into View menu and untick dot-for-dot.  Make sure the zoom is set to 100% and you can check the size manually with a ruler.

   

If satisfactory turn View -> Dot-for-Dot back on

When it comes to printing, your Windows Gimp is hopeless. Better off using something like LibreOffice. You can split the image up into A4 sized sections. Again get your calculator out A4 = 21 cm x 29.7 cm which at 22.8 pix-per-cm is 479 x 677 pixels. You can set guides up at those spacings and get separate images using Image -> Slice using Guides  This is now a big printing size 4.4 metres x 2 metres, so consider cropping before chopping up. Beware of margins when printing, these will shrink the result (typically by 3 or 4 %)  Go for marginless on the printer setup.

   

There is an application for splitting up images, You could try it: https://posterazor.sourceforge.io/

[rovingpaddy]

Rich thanks so much for this. I will have a crack at it and see how I get on.

[Ofnuts]

(01-03-2022, 03:01 PM)rovingpaddy Wrote: I had a search around but couldn't find any conclusive answers to what I'm trying to do. I'm new to the forum, so any help is very much appreciated. 

So, I need to produce patterns for making bicycle frame bags for my work. However not everyone lives local enough to do a physical drawing/pattern. So customers will email me a high res photo of their bike frame with a tape measure or ruler attached to the frame for scale.
My question is, how can I take this image from the customer and then using GIMP, make sure the image is at 1:1 scale and then print it out on multiple A4 pages? Is there even a way?

I'm very new to using GIMP so I'm completely lost at the moment.

If you can point me in the direction of any other topics or videos that may help that would also be great.

IMAGESET-FuGLi[rarbg]/' -> '../finished--Pix/MetArt/SexArt.com_22.01.03.Scarlett.Queen.Navy.Lace.XXX.IMAGESET-FuGLi[rarbg]'





Cheers
Patrick

You would need two rulers on the picture, one horizontal and one vertical. It is obvious that you sample picture was taken from eye level, so vertical dimensions are distorted by perspective and appear smaller. For instance in your picture the rear wheel is 1494px wide but only 1455px high. You can sort of fix this because you know the wheel is a circle, but there are other distortions due to the wide angle lens of the phone (so parts in the middle are slightly enlarged).

You would need to ask your customers to take the picture from far away (4 to 5 bike lengths), while kneeling down if you want usable photos.

[rovingpaddy]

(01-03-2022, 04:51 PM)rich2005 Wrote: The first thing is a measurement on the photo using the Gimp measure tool. Choose say 10 cm on the tape-measure (20 to 30 here) and determine the length in pixels. That value is shown bottom of the Gimp window.

Apologies for quality, these are photos rather than screen shots, I need to hang an actual ruler over the monitor.  Painted in a bit of green and the red is where the measure tool spans. 228.1 pixels  Go into Image -> Print Size and see what you have 



The X and Y resolution here are 72 pixels-per-inch (PPI) but might be anything depending on the camera.

Now get your calculator out and 10 cm = 228 pixels so 1 cm = 22.8  Change the units to pixels/cm and enter 22.8 in the X / Y resolutions.  By default Gimp maps the image in 1 pixel = 1 screen pixel but to see the image as it will print go into View menu and untick dot-for-dot.  Make sure the zoom is set to 100% and you can check the size manually with a ruler.



If satisfactory turn View -> Dot-for-Dot back on

When it comes to printing, your Windows Gimp is hopeless. Better off using something like LibreOffice. You can split the image up into A4 sized sections. Again get your calculator out A4 = 21 cm x 29.7 cm which at 22.8 pix-per-cm is 479 x 677 pixels. You can set guides up at those spacings and get separate images using Image -> Slice using Guides  This is now a big printing size 4.4 metres x 2 metres, so consider cropping before chopping up. Beware of margins when printing, these will shrink the result (typically by 3 or 4 %)  Go for marginless on the printer setup.



There is an application for splitting up images, You could try it: https://posterazor.sourceforge.io/

So I've had a go with the program following your instructions above and I can get the guides set and then sliced. However when it comes to printing I can't seem to be able to get it to print borderless. Even if I set the margins at 0 it still prints with a border and the image is not to scale.

I've downloaded Libreoffice but not sure how to go about getting the image in there and printing it out? I'm lost on this as I've never tried to do anything of this sort before.

[rich2005]

Not a straight forward project

This right from the beginning, with a couple of tweaks before a LibreOffice set up.

8 and a half minutes https://youtu.be/1WAC2PCSKOU






Not this image particularly but sometime you might need to temporarily straighten for a true horizontal measurement.
Deduct margins before slicing the image.
Save some ink by tracing the edges.


I am not using the Windows Gimp print, it is notoriously flaky.

[rovingpaddy]

(01-08-2022, 04:17 PM)rich2005 Wrote: Not a straight forward project

This right from the beginning, with a couple of tweaks before a LibreOffice set up.

8 and a half minutes https://youtu.be/1WAC2PCSKOU






Not this image particularly but sometime you might need to temporarily straighten for a true horizontal measurement.
Deduct margins before slicing the image.
Save some ink by tracing the edges.


I am not using the Windows Gimp print, it is notoriously flaky.

Thanks so much for this Rich, following that video was a dream. I've got it now that once the png image is in LibreOffice and I've selected original size, in the properties section it says Margin - Normal 1.90cm, this setting when printed gave me 96mm on the ruler, when measuring 100mm on the image.
If I set the Margin to Narrow, I get 98/99mm which is pretty close.

Is there a way to manipulate the pixel numbers to correct this? Or would you put it down to my printer still not printing 100% true to scale? (I did try a no margin print and that still added margins albeit very slim)

I'm a lot closer to the correct size anyway with your help, really do appreciate it. I will do a full printout on Monday and check it against the actual frame to see how it fairs.
Patrick.