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Collage for Print -- DPI & Scaling

Mar 22, 2014, 18:04
Post: #1
Collage for Print -- DPI & Scaling
Hello,
I've been using Gimp for a while but haven't made many compilation images or sent anything to a print shop.

Now I'm doing both at the same time. What I'd like to know is how to go about making a collage of several images for a quality print job. The final print piece will be 6x9. I want several images to be on each side of the print and each image is way bigger than 6x9.

So...should I make one large "workspace" pulling my images together and then once I have it formed correctly adjust the DPI and stuff? Or should I adjust the DPI/scale of each image beforehand, create a 6x9 blank workspace, and fit each in that way?

I hope my question makes sense, I may not be using certain terms correctly. Print is new to me and I only occaisonally scale images so I'm limited there also.

Let me know. Thanks.
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Mar 22, 2014, 18:38
Post: #2
RE: Collage for Print -- DPI & Scaling
Your images will print as big or as small as you want them to, adjust the pixels-per-inch (ppi).

To send off to a printer, generally use 300 ppi. A canvas 2700 pix x 1800 pix @ 300 ppi prints to 9" x 6"

Then what size are your images?
My camera is 16 MP and the images are 4600 x 3500 Four of those would make an image 9200 x 7000 pix and at 1000 ppi would print 9.2" x 7"

I could do a little cropping to get to a 9:6 aspect ratio and send that off to the printer. They might not be very happy about 1000 ppi but might accept it.
Probably your best bet is to assemble the prints you have, then scale the whole thing down to 300 (to 600) ppi.

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Mar 22, 2014, 18:42
Post: #3
RE: Collage for Print -- DPI & Scaling
some images are 16.2 MP others are 24.1MP.
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Mar 23, 2014, 10:31 (This post was last modified: Mar 23, 2014 10:51 by rich2005.)
Post: #4
RE: Collage for Print -- DPI & Scaling
I had a look around the printing services here in the UK and they are not very keen on downscaling a large image. Probably best to do that yourself.

Just my thoughts.
6" x 9" is a small print size (and some printers do not use that size). Make a canvas that will print at 300 ppi = 1800 pix x 2700 pix

Now you need to determine how many images are going into the finished work and what sort of size in pixels they need to be. At best they are going to be almost thumbnails so do not expect fine detail. If they butt in the middle then the width would be 900 pix. Only you can determine the layout. Portrait orientation versus Landscape, how will these fit together?

There are applications/plugins that will batch scale but I think you will get a better result treating each image individually. Remember lots of open images consume lots of computer resources, have the 2700x1800 image open and each 'thumbnail' one at a time. The usual advice for anything computer-ish Save your work more often than frequently Save in gimp xcf format until the montage is complete.

Have the 1800x2700 canvas open.
Open one of your images. Look at it. Do you need to do any straightening, cropping any other sort of remedial work, now is the time to do it. Now you can resize it.
Menu: Image -> Scale Image the width and height are linked together, so set one, (try width = 900) and the other adjusts. For quality Sinc(Lanczos3) and scale. Not a bad idea to maybe export this as a separate png image.

Copy that, paste in as a new layer. Use the move tool to position. Close that thumbnail and move on to the next. Remember to save your work.

Here is one where I cheated, bulk scaled the images and opened them all at once Menu: File -> Open As Layers

[Image: QYcezuz.jpg]

But it does show
Useful to set up some guide lines
Moving a layer. Easy to move the wrong layer, tick the move active layer button.
Layers can overlap and you can adjust this depending on the position in the layer stack.

Truthfully not difficult, the main issue are your large original image sizes. If they had been a bit smaller, maybe a large original canvas then scale that, but 24 MP is around 5500x4000 pix a bit uncomfortable.

Edit: I remembered this episode of meetthegimp 'Look Down'
http://blog.meetthegimp.org/192/
It covers making a mosaic, a bit advanced, but there are tips on sizing images in the video.

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Mar 23, 2014, 13:09
Post: #5
RE: Collage for Print -- DPI & Scaling
Thanks for all the advice. Fortunately I have a pretty beastly machine here with 16 GB of Ram and a nice processor. I ended up making a huge workspace and adding all my pictures to it in their original sizes, only making minor adjustments so they all have the same proportions.

Took almost all my RAM and Gimp started acting a little funny but I got through it. I have assembled the mosaic, it's about a 60 MB jpeg file exported. The quality of each image looks great in digital but I'm not sure how it'll turn out in print.

I see that I can adjust the print size and DPI within GIMP but I'll probably take it to a local print shop and make sure it'll do what I expect and ask for their advice.

THanks for all the help.
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Mar 23, 2014, 13:39
Post: #6
RE: Collage for Print -- DPI & Scaling
Nice one. Do not be surprised when their machine spits it out and they ask you to downscale it to 300 ppi. Worth taking a few different sizes and also formats with you. I found that in theory tiff was acceptable, in practice not accepted by their machine.

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Mar 23, 2014, 16:20
Post: #7
RE: Collage for Print -- DPI & Scaling
(Mar 23, 2014 13:39)rich2005 Wrote:  Nice one. Do not be surprised when their machine spits it out and they ask you to downscale it to 300 ppi. Worth taking a few different sizes and also formats with you. I found that in theory tiff was acceptable, in practice not accepted by their machine.

I can set 300ppi in Gimp though right?
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Mar 23, 2014, 16:59
Post: #8
RE: Collage for Print -- DPI & Scaling
(Mar 23, 2014 16:20)lionking Wrote:  I can set 300ppi in Gimp though right?

Seeting to 300DPI only will change the print size. In fact you have to rescale so that at 300DPI the image is the right size, and set the print definition to 300DPI. less complicated than it looks:

>Image>Scale image, set the print definition to 300DPI and give your final size in inches, Gimp will compute the necessary pixels.

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Mar 23, 2014, 17:14
Post: #9
RE: Collage for Print -- DPI & Scaling
(Mar 23, 2014 16:20)lionking Wrote:  I can set 300ppi in Gimp though right?

Sure you can.

Here is the last post in pictures (well one picture)

Image -> scale image like this but we are back to the first post about pixel sizes

[Image: Ynnp1j8.jpg]

Set X & Y resolution to 300 pixels/in & interpolation to Sinc. If you use the inches option, it still shows the pixel size 1800x2700 under the width/height box. Scale it. Export it and that is it.

Some reading for you http://www.cambridgeincolour.com/photo-e...orials.htm

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