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Quadrilateral Detection in Color Images


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Several image processing and computer vision tasks can be attributed to quadrilateral detection. Examples include automatic cropping of scanned photos, perspective correction of documents acquired with digital cameras.

The major challenge is to achieve a robust performance even in situations of low signal/noise ratio and correlated line-and-alike noise. 

Core Technology

We have developed a quadrilateral detection algorithm based on a novel color edge detector:

  • a novel color edge detector that boosts signal/noise ratio by taking local gradient orientation into account

  • a line detector fully utilizes both gradient strength and orientation

  • a detection scheme based on a metric maximization on sets of mutually non-overlapping quadrilaterals

Applications I: Automatic perspective correction and cropping of digital camera acquired document images

Assuming a complete document page is included in the image and a reliable detection of the quadrilateral boundary as well as a known aspect ratio, perspective correction and cropping can be done automatically. No assumption about the document content is necessary. 

Here is an example (all images displayed as JPEG compressed PDF):

A magazine page acquired with a HP935 DC 

Auto perspective corrected and cropped

Adaptively enhanced

Application II: Automatic cropping of scanned photos

The constraints of corner angles closed to 90 degree, as well as possibly common photo sizes, could be imposed to increase reliability. No assumption about the number of photos as well as their relative positions is necessary.

Here is an example:

Photos scanned with a HP see-thru scanner

Photos detected


For more information about the technology, please contact Jian Fan (jian.fan@hp.com) at Imaging Technology Dept., HP Labs.

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