Bad contrast with simple-scan and Canon TR4550

Hi, I am using Ubuntu 20.04 and libsane-common 1.0.32+git20210215-focal0. My Canon TR4550 scanner (wifi mode) is correctly detected editing /etc/sane.d/escl.conf file, and adding a new device line like this : device https://192.168.x.y:443 "Canon TR4550 Serie". But the contrast is not correct using simple-scan, scanned documents background is greyed, while contrast is good when using windows VM and Canon SW, see below : scan-test

Using Quality Parameters (Contrast/Brightness) has no effect. So I suppose this is a bug, I hope this is the right place to create the defect. Let me know if I miss something.

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