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How can I imread just an ROI, not the whole image?

asked 2013-03-30 12:55:58 -0500

RubeRad gravatar image

Hey all,

This seems like a really dumb question, but I've searched, and cannot find any answer.

I am working with large images -- or at least large enough that I don't want to load the whole thing into memory -- and I want to process just ROI at a time.

Is there a way in OpenCV to read just a desired ROI into memory? Or do I have to imread the whole thing, copy out my ROI and release the full image?

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Actually I think the way you are describing is actually the only possible way. I am doing exactly the same for 5000x5000 and 25000x25000 images.

StevenPuttemans gravatar imageStevenPuttemans ( 2013-03-30 13:20:51 -0500 )edit

Hmmm, maybe a feature request is in order? All it would take would be a flavor of imread with an extra ROI argument

RubeRad gravatar imageRubeRad ( 2013-03-30 14:28:23 -0500 )edit

Then you should try it to implement yourself and file a pull request. :)

StevenPuttemans gravatar imageStevenPuttemans ( 2013-03-30 16:30:22 -0500 )edit

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answered 2013-04-01 12:20:44 -0500

Seb gravatar image

You still need to read the entire binary file. But you can alter the part where OpenCV build a Mat object. You can just read your ROI from memory and create a smaller Mat object.

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Actually one you know how the binary file structure looks like, shouldn't it be possible to read a partial binary file? Just curious about this too.

StevenPuttemans gravatar imageStevenPuttemans ( 2013-04-01 13:00:41 -0500 )edit

Hi steven, I am also doing assignment on processing Selected ROI from whole image . If you have any idea or sample codes to understand the concept please help me .Thank you !!

Sharath gravatar imageSharath ( 2013-04-01 20:05:45 -0500 )edit

Like i already suggested above, only way it is working now is defining a rectangle, than using that rectangle to create a region of interest copy of the original Mat image.

StevenPuttemans gravatar imageStevenPuttemans ( 2013-04-02 02:29:06 -0500 )edit

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Asked: 2013-03-30 12:55:58 -0500

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Last updated: Apr 01 '13