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

Understand DPI, it affects many things in Scan Tailor

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univurshul
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Re: TIFF or JPEG?

Post by univurshul » 07 Aug 2010, 05:34

I would have to run a comparison test in the morning to be sure. I'll let you know what I find then.

What entered numerical DPI is better served for processing if Scan Tailor rejects the images?

My camera creates JPEGS in a format of 2448x3264. This is what I send into scan tailor. If I enter this number, typically, the image is distorted longer or wider. If I enter an even numbered ratio like 600x600 it appears correct.

Tulon
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Re: TIFF or JPEG?

Post by Tulon » 07 Aug 2010, 06:04

univurshul wrote:What entered numerical DPI is better served for processing if Scan Tailor rejects the images?
This prompted me to create a signature. The answer is there.
Scan Tailor experimental doesn't output 96 DPI images. It's just what your software shows when DPI information is missing. Usually what you get is input DPI times the resolution enhancement factor.

univurshul
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Re: TIFF or JPEG?

Post by univurshul » 07 Aug 2010, 13:06

Thanks, Tulon.

Although I do feel like a complete idiot now for prompting a signature like that...Had no idea there was a tutorial vid online that explained this concept.

Noobs.

Best Regards.

univurshul
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Re: TIFF or JPEG?

Post by univurshul » 07 Aug 2010, 15:03

After an intensive re-look at my workflow, I've determined that all of the errors in page splitting and content selection are directly stemming from my DPI input upon project creation.

It is not a Mac problem. It's my own ignorance. My apologies for any time wasted over this.

Highly recommended to all noobs on Scan Tailor (likely Mac users like myself who've finally had a chance to try this software since the 0.9.9.1 build recently became an easier install) to watch the video twice before you start processing your ebooks: http://vimeo.com/12524529

Tulon
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Re: Understand DPI, it affects many things in Scan Tailor

Post by Tulon » 07 Aug 2010, 15:23

I am going to insert a variation of my signature with a link to the tutorial right into the "Fix DPI" dialog. Entering wrong DPIs is quite a common error.
Scan Tailor experimental doesn't output 96 DPI images. It's just what your software shows when DPI information is missing. Usually what you get is input DPI times the resolution enhancement factor.

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dingodog
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Re: Understand DPI, it affects many things in Scan Tailor

Post by dingodog » 15 Aug 2010, 06:13

Dear Tulon

several times I get already scanned images (by other) I want clean with Scantailor

and several times these images have dpi settled to 0 (that is not the real dpi)

How can I find he real dpi?

Tulon
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Re: Understand DPI, it affects many things in Scan Tailor

Post by Tulon » 15 Aug 2010, 06:24

The video tutorial tells you how.
Scan Tailor experimental doesn't output 96 DPI images. It's just what your software shows when DPI information is missing. Usually what you get is input DPI times the resolution enhancement factor.

ArchCarrier
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Re: Understand DPI, it affects many things in Scan Tailor

Post by ArchCarrier » 09 Sep 2010, 12:58

I just found out that Tulon's method described in the video is not always correct. I just photographed a paperback book printed in a small font, and by using Tulon's method, the DPI comes out to 272. But when I measure the length of one line in the image (in pixels) and in the book (in inches) and divide the two, the DPI jumps up to 364! That's quite a difference.

Tulon
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Re: Understand DPI, it affects many things in Scan Tailor

Post by Tulon » 09 Sep 2010, 13:25

Sure, no one forces book publishers to fit exactly 6 lines in one inch. Still, it's a reasonable estimate that's expected to produce good results with Scan Tailor. BTW, for books with a small font size, it might be beneficial to make Scan Tailor think it's larger than it is by specifying a lower DPI.
Scan Tailor experimental doesn't output 96 DPI images. It's just what your software shows when DPI information is missing. Usually what you get is input DPI times the resolution enhancement factor.

TJ-Shredder
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Re: Understand DPI, it affects many things in Scan Tailor

Post by TJ-Shredder » 12 Oct 2010, 08:18

For Mac users as myself, finding the correct DPI works as follows.
I use the shareware GraphicConverter from http://www.lemkesoft.de/. It has some rudimentary processing possibilities and I never needed more. I bet you can do the same in GIMP or whatever...
I double click my image, which usually pop-ups Preview. I select an area ranging from side to side of the book. Then I paste it into a new document in GraphicConverter (cmd-j). Now I go to menu Picture/Size/Scale and uncheck "scale picture". Now I measure in real world the size, and enter the result into the width. For example 24.1 cm into the width form. The size dialog will now calcuate the correct DPI automaticaly...
In my case it was 389 DPI. This is very exact, but in my experience, it could vary a bit with moving from beginning to end of a photographed book. But that doesn't really matter...

I have a German version of GraphicConverter, and simply translated the German menu point to English, the real names could be different...
For explanation two picts...

Select the size:
Select_Size.jpg
Select the size
Select_Size.jpg (132.67 KiB) Viewed 4543 times
Calculate the DPI
Calculate_DPI.jpg
Calculate the DPI
Calculate_DPI.jpg (62.74 KiB) Viewed 4543 times

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