如何使用OpenCV和Java检测图像中的上下颠倒文本

Question

I face this problem for a while and still cannot figure it out.
I'm using OpenCV and Java to detect the card from image and crop it then transfrom, every thing goes fine if the original image is in correct orientation. The task for now is: How to rotate image in 180 degrees? Or how to detect the text is upside down then we can rotate it to right orientation.
The result i get from OpenCV in Java is the Mat object contains the cropped cards.
Does anyone faced and solved this before or have any idea please direct me to the right solution.
Thanks in advance.

Here is sample images i cropped from originals
Sample 1
Sample 2

Answer 1

Just run your code, and if it finds nothing on the first pass then you can just rotate the image and try again? Or you could try scanning a small portion of the card only, and then you can determine if the card is the right way up or not.

It will pay to sit down and think it through for yourself on how this might be done best.

As for rotating images, have you tried looking it up? Because if you are using a buffered image then rotating can be done with a simple AffineTransform:

AffineTransform at = AffineTransform.getRotateInstance(Math.PI, image.getWidth()/2, image.getHeight()/2.0);
BufferedImage myRotatedImage = createTransformed(image, at);

Edit: For rotating a Mat object you can use:

Imgproc.warpAffine(Mat source, Mat dest, Mat M, Size size)

Taken from: http://docs.opencv.org/java/3.0.0/