A background picture was always toned down by a fixed amount (night: x107/256,
then every pixel held to a luma of 64; day: lifted 60% toward white, held up to
200), and the lock-screen wallpaper always sat under a black veil of 105/255.
On a dark theme that left a picture barely visible. Both now take a step: Off,
Light, Medium or Strong.
- Settings > Theme > Background: "Picture dimming" under the picture's button,
shown while Image is picked; part of the page's pending choices, saved by
Apply and restart (bgImageFit applies it once at boot).
- Settings > Lock screen > Look: "Wallpaper dimming", applies the next time the
lock screen shows (veil 0 / 40 / 72 / 105).
Strong is the default and an absent key reads as Strong, so nothing changes for
anyone until they pick a step: PictureDim.h holds the per-pixel step, and
test/test_picture_dim.cpp checks Strong against the old formula on 281k
samples, plus range, ordering and the per-step readability bounds. New keys
bg_dim and lock_dim are standalone uchar keys in the settings backup list.
Three new strings, rows in every .lang, i18n_builtin.h regenerated.
V4 (no picture option there): +1624 B flash, the string table.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
