How I fixed a 0..1 brightness slider in vdu_controls (Philips Evnia DDC/CI bug)

May 16, 2026 · 9:11 PM UTC ·11 min read · 0 reactions · 0 comments · 25 views

#linux #opensource #python #debugging #ddcci

TL;DR · WeSearch summary

A bug in the vdu_controls application caused a Philips Evnia monitor's brightness slider to only show two values instead of a full 0–100 range. The issue stemmed from a malformed capability string in the monitor's DDC/CI communication and a regex error in the software. A fix was developed and merged into the upstream repository.

Key facts

▪The Philips Evnia 27M2N5500Q monitor reported the brightness VCP code twice in its capability string, including once with invalid values.
▪The vdu_controls app used an unescaped '.' in a regex, causing it to misinterpret the brightness range as 0..1 instead of 0..100.
▪The bug was isolated to user-space Python code and did not affect the monitor's actual functionality, as confirmed by ddcutil.
▪A patch was submitted and merged in digitaltrails/vdu_controls#128 to resolve the parsing issue.
▪The fix included updates to the regex handling and added test coverage to prevent future regressions.

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try { if(localStorage) { let currentUser = localStorage.getItem('current_user'); if (currentUser) { currentUser = JSON.parse(currentUser); if (currentUser.id === 3935281) { document.getElementById('article-show-container').classList.add('current-user-is-article-author'); } } } } catch (e) { console.error(e); } Mohammed Elsayed Ammar Posted on May 16 • Originally published at mammar.pages.dev How I fixed a 0..1 brightness slider in vdu_controls (Philips Evnia DDC/CI bug) #linux #opensource #python #debugging I plugged a new monitor into my Kubuntu laptop last week. The brightness slider in the tray utility I use only had two settings: black, and almost-black. Not 0 to 100. Not a continuous gradient. Just two positions. The monitor itself was fine. The cable was fine.

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