User draws a line on an image in an iOS app and access pixels on that line using OpenCV [closed]

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I am wondering how I can accomplish the following task:

In an iOS app, the user selects an image and loads it onto the screen of the app. The user can draw a line on top of the image. The line selects the pixels on which it is drawn using OpenCV and the values of those pixels (primarily intensity) are returned. I understand that there is a class in OpenCV called LineIterator, but it uses raster lines. Is there a way I can convert the line that the user has drawn on the app to a raster line that OpenCV can manipulate?