Thank you very much ! It work ! But I modify what you suggest as following:
convert *."$1" -deskew 80% -morphology Close Diamond:1 -alpha off -monochrome -compress Group4 "$2".pdf
1) Look for what I marked by red. This command specifically written to convert into PDF not other format. It is unwise to allow for chosen other format output because, for ex: compression option will not be suitable for other output format.
2) I discovered, by experience that "-sharpen 0x10" or even "-sharpen 0x1.0" tend to reverse function of "-morphology Close Diamond:1". So, it is better not to use "-sharpen" at all.
Please beware: this command (script) should to applied ONLY ON ALREADY MONOCHROME (BLACK & WHITE) IMAGES. If you have colored image you should convert them 1st to monochrome images before process them by this command (script) ........ .