@AriJeannin , thank you very much again!
I tried different options for creating RGB-images, including the one suggested by @marpet with snappy ImageManager.getInstance().createColoredBandImage:
Save image from Sigma0_HH_db band with snappy
And the best and most convenient result was obtained with using rasterio. It works really very fast using my functions with numba - GPU accelerator! Raster data is read very quickly and I can use my own functions to implement various image processing.
After processing I normalize each of the channels using the OpenCV library, create a numpy array and write each of the channels to it. The process of creating an image is much faster than using snappy.
Thank all of you so much for your help!