VectorPaint day-and-night diptychs: preserve geometry while changing light and colour

English translation of the Chinese original, translated on 2026-10-27. Original publication dates, attribution, code and version notes are retained.

Day and night versions reveal how colour changes a scene. Fix the window, table and plant geometry before changing sky and light. This static colour exercise does not calculate time, sun position or real illumination.

List fixed and changing elements

Define shared window, table, pot and plant geometry and changing sky, room values and lamp state. Build one structural baseline on an 800 by 1000 pixel canvas. Separate colour comparison from composition changes and name useful layers so the night copy remains easy to maintain.

Build a scene that works without lighting effects

Construct simple window, table and plant shapes and inspect separation in neutral values before effects. Make interior/exterior stacking deliberate and keep sky/glass separate from the frame. Duplicate from an editable baseline rather than reimporting PNGs so each version retains controllable objects.

Set the main light area in the day version

Use the window as the brightest area, with a slightly darker room and distinct plant silhouette. Keep any table light patch consistent with the window direction. Establish broad relationships with a small palette, preserving edges. Reduce excessive outdoor saturation or decoration before outlining every indoor object. Record the day palette.

Rearrange the value hierarchy at night

Darken the sky and broad room areas, then introduce limited lamp or reflected highlights. A uniform blue overlay does not automatically correct local light relationships. Keep geometry unchanged and ensure the frame and plant remain legible. Warm light against cool surroundings is one option, not a mandatory rule.

Compare both panels under equal conditions

Compare equal-size previews on equivalent viewing backgrounds. Audit shared contours before value relationships. Detail may differ intentionally, but major geometry should not drift. Fix mismatched positions in editable sources rather than patching exports. Label day/night and revisions clearly to prevent mixed structural versions.

Test one light-source change

Turn off the lamp in a test and inspect areas it previously illuminated. Adjust related highlights individually rather than darkening everything. Restore the lamp and record linked shapes. Ordinary objects do not automatically associate lights with highlights, so maintain those relationships manually and keep the experiment separate.

Check dark details and peak highlights after export

Save both sources and inspect exported dark separation and bright edges in the intended placement. Keep canvas, margins and title treatment consistent for a diptych. Name day/night, size and revision explicitly. Printed use needs its own proof because subtle screen differences may not survive on paper.

Revisit values when only the background changes

If only the sky differs, revise indoor light relationships too. Restore key night contours without brightening everything. A flash-like day scene may need broader ambient light. Correct geometry mismatches before comparing palettes. Greyscale should show a clear hierarchy in both versions before colour adds atmosphere.