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Diffstat (limited to 'content/posts/adaptive-binarisation')
| -rw-r--r-- | content/posts/adaptive-binarisation/index.md | 27 |
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diff --git a/content/posts/adaptive-binarisation/index.md b/content/posts/adaptive-binarisation/index.md index 0060f44..4266343 100644 --- a/content/posts/adaptive-binarisation/index.md +++ b/content/posts/adaptive-binarisation/index.md @@ -1,6 +1,31 @@ --- title: "Adaptive Binarisation" -date: 2019-10-02 +date: 2019-12-17 draft: true categories: [binarisation, preprocessing, image manipulation] --- +The [previous post](/posts/binarisation-introduction) covered the +basics of binarisation, and introduced the Otsu algorithm, a good +method for finding a global threshold number for a page. But there +are inevitable limitations with using a global threshold for +binarisation. Better would be to use a threshold that is adapted +over different regions of the page, so that as the conditions of the +page change so can the threshold. This technique is called adaptive +binarisation. + +For each pixel of an image, adaptive binarisation considers the +pixels around it to determine a good threshold. This means that even +in an area which is heavily shaded, for example near the spine of a +book, the text will be correctly differentiated from the background, +as even though they may both be darker than the text in the rest of +the page, it is the darkness relative to its surroundings that +matters. + +<!-- +(diagram showing 2 different areas of a page, one light and one dark, +comparing global and local thresholding [can be fake, as the global +threshold diagram was]) +(actually can probably just have a dark area of a page, comparing global +and local thresholding, setting the global one such that the image is +screwed up) +--> |