Daniel Reetz, the founder of the DIY Book Scanner community, has recently started making videos of prototyping and shop tips. If you are tinkering with a book scanner (or any other project) in your home shop, these tips will come in handy. https://www.youtube.com/channel/UCn0gq8 ... g_8K1nfInQ

How to get desired dpi?

Everything camera related. Includes triggers, batteries, power supplies, flatbeds and sheet-feeding scanners, too.
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leescott
Posts: 19
Joined: 29 Apr 2010, 03:17

How to get desired dpi?

Post by leescott » 15 Aug 2017, 23:01

I use canon m2 ,but get 72dpi image.
viewtopic.php?f=15&t=3234
The DPI is determined by the sensor on your camera and the zoom level/distance.
How to get desired dpi,such as 300dpi?How to calculate.
And more,what's the most ideal distance?
Thanks!

duerig
Posts: 343
Joined: 01 Jun 2014, 17:04
Number of books owned: 1000
Country: United States of America

Re: How to get desired dpi?

Post by duerig » 15 Aug 2017, 23:34

Every camera sets the DPI field to a default value on each image regardless of 'actual' DPI. To get the DPI, take a photo of a ruler. Then calculate the number of pixels it is to get one inch on the ruler. You can change DPI by moving the camera towards or away from the page you are photographing or using zoom.

The ideal distance from the camera to the platen is complicated. The closer it is, the more likely that you will see lighting reflections and that the camera itself will end up casting a shadow. The further away it is, the more you have to zoom.

As a point of reference, the distance between the cameras and the platen in an Archivist Quill is 565mm. You might use that as a starting point and then adjust it if you notice problems.

Best of luck.

-Jonathon Duerig

leescott
Posts: 19
Joined: 29 Apr 2010, 03:17

Re: How to get desired dpi?

Post by leescott » 16 Aug 2017, 21:17

https://neilvn.com/tangents/image-size- ... pi-300dpi/
http://www.schillers.com/file-resolutio ... c-printin/
http://www.scantips.com/calc.html#result

The image size is described completely by just the pixel dimensions, dpi just relevant to printing resolution,scanning resolution or display resolution.
For us,Canon turning to 300 dpi could be more comfort.

cday
Posts: 215
Joined: 19 Mar 2013, 14:55
Number of books owned: 0
Country: UK

Re: How to get desired dpi?

Post by cday » 17 Aug 2017, 12:39

The camera image has pixel dimensions, and the image DPI can be set to any desired value using [freeware] image editing software.

If the object is to scale the image to the original page size, that can similarly be done directly by setting the image 'canvas' size...

Konos93a
Posts: 83
Joined: 19 Sep 2016, 10:00
E-book readers owned: kobo aura,kindle 1
Number of books owned: 3000
Country: greece

Re: How to get desired dpi?

Post by Konos93a » 18 Aug 2017, 09:31

with abbyfinereader you can check the recommend resolution https://www.youtube.com/watch?v=spEcHXkFmDM ((7.11))

play with the zoom and the distance and find the best one . with more than 500 dpi you are perfect .

upload a photo of your scanner

qv_
Posts: 38
Joined: 01 Jul 2014, 17:33
E-book readers owned: iRiver
Number of books owned: 1000
Country: Sweden
Location: Sweden, Södermanland

Re: How to get desired dpi?

Post by qv_ » 01 Sep 2017, 05:30

If the paper that you like to scann have a side that is 10 inch long and you like to have 300 dpi you need av sensor in your camera that is 300dpi x 10 inch = 3000 pixel wide.

Then you have the optical losses in the lens that is minimum 10%
Now you need 3300 pixel wide

This will work if the lens is a "prime" and your light is perfect.

If you use LED light and a "kit lens" you need more pixel.

I try to get 300dpi on a A4 paper (215 x 297mm) with a Canon D550 18-55 kit lens (18 Mpixel) and maybe it can be made possibole.
Att least in the midel of the page. I am not so shoure about the egde.

But soon after some years in reast now I will start the project again
IMG_3080.JPG
I am soon ready with my new workshop

qv_
Posts: 38
Joined: 01 Jul 2014, 17:33
E-book readers owned: iRiver
Number of books owned: 1000
Country: Sweden
Location: Sweden, Södermanland

Re: How to get desired dpi?

Post by qv_ » 01 Sep 2017, 05:47

This if your copy of the scann is 1:1

If you scann in 300 dpi you can look on the picture on the screnn (72dpi) and it is bigger than the scann.
You can print the same scann in 1000dpi if the copy is small enought.

But if you scann a paper in 300 dpi and print it in the same size you vill print in 300dpi

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