Extracting region(s) from parking ticket

edit

1 Scan your ticket with a flatbed scanner and use black background.

1.1 If you cannot scan, make sure the ticket is flat and take a picture. You can flatten the ticket by putting it under a flat glass, but then you need to make sure there are no reflections (shoot at an angle and see 3.1)

2 Threshold your image to get the region of your ticket.

3 Use findContours, then find minAreaRectangle of the largest contour and straighten your ticket by:

3.1. Get 4 corner points and warpPerspective your ticket to a predefined size.

3.2. If you scan you can simply counter rotate your ticket by your RotatedRect.angle, however if you put your ticket carefully, it should be straight enough, so you can skip the entire point no 3.

4 Having a straight ticket of known size, set ROIs to afore measured regions of interest and pass them to tesseract.

You can use the "Scene Text Detection" code under the object detection module:

http://docs.opencv.org/trunk/modules/objdetect/doc/erfilter.html

It seems the image you provide is with alpha channel, where as you said the white region is complete transparent(alpha = 0), so just do the following.

• Load source with alpha, you should set flags = -1 on imread().

• Now split image in to four channel.

  Mat splitedBGRA[4];
  split(src,splitedBGRA);
  

Note that OpenCV channel order is BGRA.

• Now threshold alpha channel, you should use THRESH_BINARY_INV.

• Find contour and calculate bounding box for each contour.

See the result I got with the above algorithm.