Handbook:Advanced Server Configuration:Copy Quality Checking

HylaFAX will automatically check the quality of received facsimile and regenerate rows of data that have errors in them. This facility is termed copy quality checking and is only done if the modem is incapable of doing this task itself, or if the software is configured so that modem copy quality checking is disabled.

Copy quality checking is automatically done in the server for Class 1 modems. To configure copy quality checking directly in a Class 2 or Class 2.0 modem--when the modem is capable--setup the Class2CQCmd parameter for the modem. For example,

Class2CQCmd: "AT+FCQ=1;+FBADMUL=5;+FBADLIN=10"

This enables copy quality checking for receiving and sets the copy quality parameters so that acceptable page quality requires that no more than 10 consecutive bad rows of data may be present and less than 5% of the rows in a page have errors in them. To disable copy quality checking in the modem use

Class2CQCmd: AT+FCQ=0

If a modem indicates that it supports copy quality checking but Class2CQCmd has not been specified then HylaFAX will note this when the modem is prepared for use.

Copy quality checking in the server (for any style of modem) is controlled by two configuration parameters: PercentGoodLines and MaxConsecutiveBadLines; see hylafax-config(4F) for more information. These parameters define the criteria by which the server decides if a received page has acceptable copy quality. Pages that are deemed unacceptable are rejected and the sender is told to resend the page.

Beware that many fax machines are incapable of resending pages that have unacceptable copy quality because they do not buffer a full page image.

If you encounter problems with the copy quality checking support you can disable it by setting either the PercentGoodLines or MaxConsecutiveBadLines parameters to 0; e.g.

PercentGoodLines:      0      # disable copy quality checking

Note however that doing this means you may receive facsimile that are unreadable.