How can use other part of cropped image?

I want to omit part of image, first cropped useless part of image, then I don't know how to extract other part of image.

[Rik]

What do you mean? If you succeeded in cropping the image, you achieved your goal right?

[Mohammadreza]

NO,For example I cropped red part and now I need blue part of image.

[Rik]

So you want a mask that marks the blue area with true and the red area with false?

[Image Analyst]

How do you want to handle the "hole" in the blue image that would result from the missing reddish part? Have it be black? Or do you just want a 1-D list of all blue pixel values (i.e., NOT an image)?

[Mohammadreza]

thank you Image Analyst; I find answer of my question after read your comment.