How to ESTIMATE straightening angle?

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Rick_R
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How to ESTIMATE straightening angle?

Post by Rick_R »

Okay, here's a weird problem I have ...

I mainly use PSP for retouching scans, either of yearbook pages or books. In most cases, particularly books that are not letter-size (few are), once the pages are scanned the process involves two custom steps:

First create and save a selection marquee, then select the Move tool
  • straighten the page horizonally
  • load the selection marquee
  • Turn on Edit selection
  • Move the marquee to cover the page
  • Turn off Edit Selection
  • Shift-R to crop to selection
  • Ctrl-S to save, Ctrl-F4 to close
I'm running into a problem with the straightening: I have done so many pages that I can literally tell "that just doesn't look quite horizontal" when it is off only one-tenth of a degree.

It doesn't sound like a big deal, but when you're doing it with 150+ images it adds quite a bit of time! Some of the images are obvious -- half a degree or more. But I'm routinely correcting .25-.35 of a degree. I don't know that until I have set the horizontal line -- and at that point the only thing left to do is click the check mark to make the change.

I know about setting grid lines, but I can't do that. Usually it is white pages on a scanner white background, so the page edges show up as slightly gray lines. Even if I use something like red grid lines they are just too distracting.

Anybody have any suggestion on a way to guesstimate the angle?

By the way, the book scans are basically for personal use -- these are books about 30+ years old that won't ever be on Kindle because they're still under copyright, the authors died years ago, and the books are not the type that would draw a large readership if they were republished, so no one is going to try to determine the current copyright holder and negotiate electronic publication rights. I mainly do this because the type size is difficult for me to read and I can enlarge it on a tablet.
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Re: How to ESTIMATE straightening angle?

Post by photodrawken »

Rick_R wrote: Anybody have any suggestion on a way to guesstimate the angle?
Why don't you simply use the Straighten Tool? You can also have it automatically crop the corrected image.

If you are using the Straighten Tool, be aware that any method of calculating an angle in the image is going to require drawing a line -- so if you're not getting the line right with the Straighten Tool, you ain't gonna get it right with a measuring tool....
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Re: How to ESTIMATE straightening angle?

Post by Cassel »

You CAN get the exact value if you want. If you are using the Straighten tool, and adjust the line, you should see, in the Tool Options Palette, there will be a setting called Angle. This will change as you change the angle of the line.

But of course, as said above, you can just use that tool and it will straighten it for you without calculations.
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Re: How to ESTIMATE straightening angle?

Post by Jean-Luc »

Rick_R wrote: Anybody have any suggestion on a way to guesstimate the angle?
You may also use another software.
Often OCR softwares (PapertPort, Abby, etc.) or Acrobat Pro (not Reader) straighten the pages automatically.
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Re: How to ESTIMATE straightening angle?

Post by Rick_R »

Sorry, but the people responding don't understand the problem.

I am using the Straighten tool. That's why I know the precise angle.

What I'm saying is that when I look at the unadjusted image my reaction is, "That doesn't look quite horizontal ..."

Then when I set the the Straighten tool's line I see that indeed the image isn't horizontal -- but it is maybe 0.15 degrees "off" from horizontal.

At that point I could say, "Well, it's not worth straightening" and just cancel the straighten. But at that point I might as well finish.

If knew from guesstimating that it was only 0.1 or 0.2 degrees, I'd say, "Well, that's close enough -- no point in straightening."

Regarding Omnipage, Acrobat Pro, etc., Acrobat Standard costs $300 (I have Standard 9.5, but unfortunately I missed Adobe's "only last two versions qualify for upgrade pricing" by days when they came out with the latest version.) I tried Omnipage on the yearbooks and it was absolute garbage -- it interpreted everything as text -- even homeroom photos. For one page consisting mainly of photos the "text" recognition showed over 400 "errors"!

Plus, for yearbooks I want the high-quality images, not "mysterious and magical transformations whose details are hidden from the user." One thing I did with those was send high-quality image files to my hometown Historical Society. The images (even of B/W pages) were RGB 400dpi PNG's, but with the screen resolutions now available, in 20 years we can expect that those would be considered "low resolution".
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Re: How to ESTIMATE straightening angle?

Post by LeviFiction »

What do you consider an insignificant angle? At what angle does it become worth adjusting for? Is .3 too much? Or does it have to be a full degree?

Off hand I'd say if it only barely doesn't look right, you can assume the angle is not that bad.

I can give you the basic equation for calculating angle. ArcTan((y2-y1)/(x2-x1)) But I don't think that translates properly to pixels. I made an image 2500x2500. Set the first point of the straighten tool at 5x1, 1116y1 and 2001x2, 1215y2. Using that equation I get 2.89 degrees but PSP gives 3.0.

Basic way of looking at it, the closer the difference in y is to the difference in x the larger the angle. If you're talking a 100th the difference that's about half an angle. But that's just guessing on my part. Maybe look at the difference in height of pixels every 100 and see how far it moves. 2 pixels or more per 100 is at least a single degree. Just a thought.

Of course the straighten tool is pretty simple and fast as well.
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Re: How to ESTIMATE straightening angle?

Post by Jean-Luc »

Rick_R wrote:Sorry, but the people responding don't understand the problem.
Probably.
Do you ask US to decide if YOU need or don't need to straighten ?
:D
I'm sure, I don't understand the exact problem.
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Re: How to ESTIMATE straightening angle?

Post by hartpaul »

I don't understand either.
From what I gather pages are being scanned and some are a bit askew. Your method of using a selection, edit selection etc seems a roundabout way of getting a final straightned image with only the page there.
I would: in windowed mode
1. Load the scanned image
2. Use the straighten tool but with auto crop unchecked. This will give you a straightened image on a slightly larger canvas. You can just double click to get the straighten to operate - no need to go up to the tick.
3. Use the crop tool and click one corner and drag to diagonal opposite corner. Hit enter key to accept, then hit the X to close and hit Enter again to accept the default Yes.
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Re: How to ESTIMATE straightening angle?

Post by LeviFiction »

The way I understand it the problem is simple. He knows the image is off but doesn't know the exact angle. And doesn't want to have to bring out the straighten tool every time just to check the angle and determine it's unnecessary to straighten. Thus wasting time. He already uses the straighten tool, he just doesn't want to have to drag out the tool and points every time he's unsure of the angle.

So he wants a method of estimating the angle of a straighten so that he can determine it's too crooked and needs to be straightened vs only slightly crooked and it won't make a difference. I figure once he gets used to the sight of what a large angle looks like vs a small one he can just make that determination on sight. And gave him a general estimation rule. But I think it'll be faster to use the straighten tool.
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Re: How to ESTIMATE straightening angle?

Post by photodrawken »

LeviFiction wrote: So he wants a method of estimating the angle of a straighten so that he can determine it's too crooked and needs to be straightened vs only slightly crooked and it won't make a difference.
I think you described the request correctly, but the request sounds silly -- "Gee, I know the image is crooked, but I don't know if I want to bother with it."
LeviFiction wrote:But I think it'll be faster to use the straighten tool.
+1 :lol:
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Re: How to ESTIMATE straightening angle?

Post by hartpaul »

Well to be sure, since he does not want to use guides, you could put a bit of masking tape across the screen making sure it is definitely horizontal (use a carpenter's level) and then line your image up with that and place a protractor against the screen and see if the angle is big enough. :wink: :lol: :?
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Re: How to ESTIMATE straightening angle?

Post by photodrawken »

hartpaul wrote:... and place a protractor against the screen and see if the angle is big enough. :wink: :lol: :?
I like that! You could also nail the protractor's zero point to the screen for a permanent solution. :lol:
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Re: How to ESTIMATE straightening angle?

Post by Rick_R »

LeviFiction wrote:The way I understand it the problem is simple. He knows the image is off but doesn't know the exact angle. And doesn't want to have to bring out the straighten tool every time just to check the angle and determine it's unnecessary to straighten. Thus wasting time. He already uses the straighten tool, he just doesn't want to have to drag out the tool and points every time he's unsure of the angle.

So he wants a method of estimating the angle of a straighten so that he can determine it's too crooked and needs to be straightened vs only slightly crooked and it won't make a difference. I figure once he gets used to the sight of what a large angle looks like vs a small one he can just make that determination on sight. And gave him a general estimation rule. But I think it'll be faster to use the straighten tool.
The problem is telling a small angle from a really, really small angle. More and more I'm running into, "That looks slightly off ..." and it turns out to be 0.1 degree or 0.12 degree. I can easily tell 0.4 or 0.5 -- not the specific number but "definitely needs straightening".
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Re: How to ESTIMATE straightening angle?

Post by Jean-Luc »

LeviFiction wrote:The way I understand it the problem is simple. He knows the image is off but doesn't know the exact angle. And doesn't want to have to bring out the straighten tool every time just to check the angle and determine it's unnecessary to straighten. Thus wasting time. He already uses the straighten tool, he just doesn't want to have to drag out the tool and points every time he's unsure of the angle.

So he wants a method of estimating the angle of a straighten so that he can determine it's too crooked and needs to be straightened vs only slightly crooked and it won't make a difference. I figure once he gets used to the sight of what a large angle looks like vs a small one he can just make that determination on sight. And gave him a general estimation rule. But I think it'll be faster to use the straighten tool.
Now, I understand too... Thank you LeviFiction.

The answer is simple : a simple solution doesn't exist.
To be exact, a simple solution exists :
-> View
-> Grid
The grid could help to decide if a document needs to be straightened.
But I don't know if the grid is enough precise for the task.

As some other softwares have automatic straighten tool, we could suggest Corel to develop such an improvement for a future version. As many people scan photos or text documents, this could be a "plus" for PSP.
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