How to choose suitable segmentation process for image processing Hello I'm new on image processing. 

I know there are a lot of threshold and region growing algorithms to use. 

But I would like to know what is the trick for choosing suitable method for an image ?

Currently I'm trying to extract characters from this image



and most of the methods I've tried didn't really satisfy me. So I thought maybe I am doing it wrong. Here are some samples. 

Normal Threshold



Sobel 



Adaptive Threshold
The thresholding techniques that you would find here should be ideally suited to OCR applications. You could read and easily implement. They are also very efficient.