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Thank you for posting your query, I'll be more than glad to help you.
I understand that you are unable to scan a page with data on it from your HP ENVY 4523 All-in-One Printer.
In order to isolate the issue, you need to make a copy from the unit and check.
Also, you may follow the step by step guide to reset the printer:
1.Turn the printer on, if it is not already on.
2.Wait until the printer is idle and silent before you continue.
3.With the printer turned on, disconnect the power cord from the rear of the printer.
4.Unplug the power cord from the wall outlet.
5.Wait at least 60 seconds.
6.Plug the power cord back into the wall outlet.
7.Reconnect the power cord to the rear of the printer.
8.Turn on the printer, if it does not automatically turn on. The printer might go through a warm-up period. The printer lights might flash, and the carriage might move.
9.Wait until the warm-up period finishes and your printer is idle and silent before you proceed.
NOTE: HP recommends connecting the printer power cord directly to the wall outlet.
Sorry but that was the fiirst thing i did. In this electronic age if it fails, turn it off and on again is standard practice.
It seems to be a memory issue in that I have scanned succesfully pages of about 823 KB but what keeps failing is a scan of a scan of graph paper and it makes the whole page look darker and I wonder whether there is a memory allowance to scan to my laptop somewhere?