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Author Topic: Does this sound practical? High res scanning of over-sized prints.  (Read 20422 times)

Marcel

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Re: Does this sound practical? High res scanning of over-sized print
« Reply #15 on: June 04, 2014, 02:38:18 PM »
@Marcel: I thought about moving the print as well. Both methods have their challenges.  Ultimately, moving an A0 foldout attached to a thick A2 book with binding falling apart would require a very sturdy platform to avoid any changes in the position of the foldout. I think moving the camera will be simpler for our purposes.

With the Canon 5D we'd be (hopefully) looking at imaging A4 sections of the print. At the angle used in this test I think you're right. The depth of field was pretty good but there was a bit of drop off in sharpness across the image. We have wired releases for our camera, and for this test I was using the self timer to avoid camera shake. Getting rails built shouldn't be too much of a problem but I will have to make a case for it and it will take a bit of time.  A counter-weighted pole might be a better interim method for positioning the camera while we sort out the exact specifications for a set of rails.

Yes, you would need some kind of platform with wheels and put the print on top. With an A0 sized print that is not very practical.

Rails are not crazy expensive, especially if you buy the budget version (you don't need the kind of tolerances that are needed for CNC machines, as long as it slides smoothly it's fine). Here is a link to supported round rails (it's a webshop where I buy my Bosch profiles, just to give an indication of the prices):

stappenmotor.nl/Steppermotor/linear%20guide%20ways/supported%20linear%20ball%20bearing%20for%20cnc/supported%20linear%20guideway%20for%20cnc.htm

Do you plan to automate it, or move the camera by hand? If you want to cover an A0 print with A4 sized shots then that is quite a lot of photos (including overlap).

I would love to have a fully automated XY rig myself, also to be able to do reproduceable tests with Photoscan.



bigben

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Re: Does this sound practical? High res scanning of over-sized prints.
« Reply #16 on: June 04, 2014, 09:32:36 PM »
I understand :)

I'd love to see results of this method. Are you planning on uploading everything to high res viewers ?

I'd love too see them delivered in a high res viewer too but I sadly doubt that would be the case. At best it may be 200dpi PDFs (because of their physical size they still look pretty good) and at worst, 1280px JPEG depending which collection they go online with. Those decisions are way out of our control. We'll probably make a page to describe our use of this technique which will include a full res sample or two.

@Marcel: we'd probably get Engineering to help us build something. As much as I'd love to motorise it we'll probably end up with some pulleys and string marked off at fixed increments or something like that. It will be a lot of photos, although this test only had about 50% overlap. The edges of the page could definitely benefit from higher overlap, particularly at the spine of the book, and at a smaller fov there may also be  a need for more overlap in areas of consistent patterns.

bigben

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Re: Does this sound practical? High res scanning of over-sized prints.
« Reply #17 on: September 01, 2014, 09:47:01 AM »
A couple of larger foldouts have come our way and it looks like I'll be getting the go ahead to set up a prototype. To fit the range of prints I've seen so far we're looking at a working area of about 2.5 x 4m.  Given the size of this area we'll have to have some lighting that moves with the camera. The first few tests will probably be hand held while the lighting rig is sorted out so we know what sort of weight we're dealing with, possibly some LED video lights on brackets.