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I am working in digital image processing field, recently I am studying about Image Noise, I just want to know that whether this noise removal is part of image enhancement or image restoration.

I have read some papers on it, at some points authors are saying that image enhancement from a given noisy image, and on the other hand in some papers authors are saying that noise removal is image restoration process.

Please explain what is correct?.

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    $\begingroup$ Both are right. $\endgroup$ – Eddy_Em Oct 1 '13 at 14:09
  • $\begingroup$ Sir, please specify that in which case image noise removal would be image enhancement and in which case it would be image restoration. $\endgroup$ – Mayank Tiwari Oct 1 '13 at 14:14
  • $\begingroup$ It's task dependent: if you just want to make image "more beautiful" to print it, you would call noise removal "image enhancement"; if you want to make some kind of image processing and noise will strongly worsen resulting data, you will call it "image restoration". Another way is restoration of broken and/or old photos: they have many corrupted zones. But in that case you can't call corrupted zones noise because of their origin. $\endgroup$ – Eddy_Em Oct 1 '13 at 15:30
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If you want work in the image processing field, my first advice would be to try and understand various techniques, tools and algorithms used, understand how they work, where and why they are applied and what you can achieve by applying each of them to your input without actually trying to classify them into labeled boxes.

Unfortunately, terminology is not perfect and it is hard to reach a naming consensus even concerning high level concepts, let alone detailed techniques.

But, about noise and noise removal: First, it is important to understand that noise can appear in the image for various reasons most of which could be classified to:

  • noise introduced by the sensor (camera, film, circuitry)
  • "digitally" introduced noise (errors in transmission, lossy compression)

And I would say that noise removal could be part of both processes of image enhancement and image restoration. The opinions are based on my own intuition as somebody who's been working in image processing for a few years now, but:

  • Image enhancement

    If I got an image from a bad-quality sensor, or simply wanted to increase the details on any image obtained directly from a camera, I would call it image enhancement.

    An example I saw and would probably classify as such is processing of satellite images. Usually, before processing the image, you want to enhance the contours and remove small intensity variations.

  • Image restoration

    If something corrupted the image you got from the sensor and you want to revert back and obtain an image as close to the original, sensor-returned image, I would call it image restoration.

    An example could maybe be trying to correct the images (frames) while video streaming, where you would want to handle the losses as much as possible and still display a (good) video.

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It depends on the final goal and the model used.
If we assume we have an image - $ I $ which is a result of a sum on of an image $ W $ with noise $ n $: $I = W + n$ and our goal by reducing the noise is estimating $ W $ than this process is restoration.

Yet I could try achieving a different goal by denoising, such as making it look better (Subjective target) or use prior such as Piecewise Constant image which means the denoising process if more of an enhancement to the image.

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