[HN Gopher] Unprojecting text with ellipses (2016)
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Unprojecting text with ellipses (2016)
Author : nmstoker
Score : 138 points
Date : 2024-05-19 21:08 UTC (1 days ago)
(HTM) web link (mzucker.github.io)
(TXT) w3m dump (mzucker.github.io)
| lupire wrote:
| Why is this better than simply finding the bounding quadrilateral
| of the text, and rectangularizing that?
| dahart wrote:
| Good question. How does one simply find the bounding quad of
| rotated perspective text? Will that handle perspective
| distortion?
|
| I guess the author partly answers your question early on with
| discussion of the Merino-Gracia paper, which fits a quad to
| individual lines of text, and a comment about how that relies
| on first being able to detect lines of text.
|
| Matt also doesn't claim this method is better. He says "I'm
| sure its neither as accurate or as useful as the Merino-Gracia
| approach." I assume the example text "Needlessly Complex" is a
| bit of self-deprecating humor, acknowledging he may not be
| taking the easiest path there is. But the method here seems
| interesting and useful to me for its approach; it doesn't have
| to identify word or page boundaries, or lines of text, as a
| prerequisite. The assumptions are simple and the optimization
| is simple, it's a nice study in different ways to think about
| the problem.
| yorwba wrote:
| The method does have to identify lines of text to find the
| rotation angle, but doing so after perspective correction
| using the "all letters should be about the same size"
| assumption means that a Hough transform is enough for that
| step, since the lines should already be roughly parallel.
|
| (Having to identify page boundaries is handwaved away with
| "I'm going to make a huge simplifying assumption that that
| the image we're processing basically contains only the text
| that we want to rectify")
| lupire wrote:
| Finding linear boundaries of a wile block of text is much
| easier than finding letter boundaries. It's a 1980s textbook
| matter of finding lines where the brightness gradient is
| extremely large.
| dahart wrote:
| Which algorithm are you referring to? I have a copy of Jain
| et al and I can't find what you're describing. Do you have
| a link to something? The Hough transform is used in this
| article, if that's what you're thinking of, but that will
| not work to find the bounding box of text, the lines have
| to be solid, contiguous, and linear for that to work. Note
| the method in the article doesn't depend on the text having
| a solid surround color, or even have the text arranged in a
| roughly rectangular shape. And it also doesn't depend on
| the text being linear. These differences are valuable, not
| having to make the same assumptions you're making, and it
| means this method (whether or not it's "better") may work
| in a wider variety of situations, or may make a very good
| complement to existing methods.
| kookamamie wrote:
| As the blog title has it, it's needlessly complex.
| ch33zer wrote:
| Never have unprojected text. I learned the hard way it's just not
| worth it.
| alex_duf wrote:
| If you never have done it, how can you have learned the hard
| way that it's not worth it?
| thsksbd wrote:
| Since we're nitpicking, OP said:
|
| "Never have unprojected text."
|
| Not:
|
| "I never have [...]"
|
| The absence of an explicit subject means that another correct
| interpretation of the sentence is that the OP is giving you
| some good advice.
| lupire wrote:
| Good advice about what? Unprotected text is worse than the
| alternatives, projected text, or not text at all?
|
| That's an outrageous claim that needs some sort of
| justification.
| thsksbd wrote:
| A valid interpretation of the OP's sentence includes the
| advice never to have unprojected text.
|
| Im not evaluating the worth of said advice, just the
| grammar, to play nitpick tennis with alex_duf who
| graciously conceded the point.
| alex_duf wrote:
| I see! I had failed to parse the sentence!
| ClassyJacket wrote:
| What would I have to learn to understand all the maths in this
| post?
| BobbyTables2 wrote:
| It's only basic pre-algebra and matrix multiplication. Plus,
| the typical Mathematicians' love of variable naming and use of
| the tilde.
|
| Matrix equations are really just shorthand for several related
| equations. The notation can be a bit unsettling if you aren't
| used to it.
| DeathArrow wrote:
| Linear Algebra. A point in space can be though as a vector.
| Rotation and scaling are done by multiplying a vector with a
| matrix.
| tlarkworthy wrote:
| As all the classic computer algorithms are here
| https://homepages.inf.ed.ac.uk/rbf/HIPR2/index.htm
|
| E.g. https://homepages.inf.ed.ac.uk/rbf/HIPR2/hough.htm
| DeathArrow wrote:
| I wonder how well does it work for images. There is going to be
| some data loss, but how much?
| Someone wrote:
| Not at all for most photos, I think. What would you replace the
| assumption _"on average, all letters should be about the same
| size"_ with?
| JadeNB wrote:
| I thought at first that it was about
| https://en.wikipedia.org/wiki/Ellipsis , which makes sense in a
| textual context, not about https://en.wikipedia.org/wiki/Ellipse
| , so it took me a minute to understand the relevance of the
| article.
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(page generated 2024-05-20 23:01 UTC)