Please give an example or specify your question.
no pixel value
sorry, but this is impossible to answer without more information on what data you are using and what processing you applied.
when downloading a sentinel 2 image and opening band 7, I found pixels with no reflectance value (Nan), my question is how to correct those pixels in SNAP.
Is there a tool to make that correction?
banding error correction
you can correct in SNAP the banding or loss of rows and columns of pixels. These zones can be assigned a mean value between the top / bottom or front / back line.
you can check if there is a valid pixel expression in the band properties. If you remove it, all pixels will be displayed.
But keep in mind that these pixels were masked for a reason, so you have to be careful when you analyze the results.
The image scenes of S2 are not always fully filled with data.
You will often see images like the following:
The empty no-data area varies in size. Do you mean this?
This cannot be filled. Applying a mean makes no sense.
If you see single pixels in the data which are set to no-data those could be filled with an image filter for example.
You find the filters in the menu at ‘Raster / Filtered Band’.