Original painting, overlaid for comparison

The Daughters of Edward Darley Boit

Sargent, 1882 · 222 × 223 cm · Museum of Fine Arts, Boston. One room, three light sources, and a mirror that reflects one of them. All paintings

Walk: drag to look, W A S D to move, Q E for height, Shift to run.

The three lights

Switch each light on or off and move it. The room stays fixed, so only the lighting changes. Fade the painting over the render to judge.

Show light positions

What is the mirror reflecting?

The mirror hangs flat on the alcove's right wall, across from the vase, and faces left. The viewer sees it edge-on. The dashed line is the viewer's sight line into the glass and out again.

Wall position1.00 m Show the sight line

In Fast preview the glass is a true planar reflection. In Path traced mode it reflects with full bounces.

Which combination fits?

Tonal match with the painting, current setting

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The match compares the pattern of light and dark, not colour, so a clay room can score well only if the light falls in the right places. It uses the fast preview and the Viewer's eye view.

Check against the painting

Overlay Difference blend Floor grid (0.5 m) Measure: click two points

Rendering

Fast preview Path traced

Path tracing adds bounce light from the walls, floor and rug. Samples: 0

Bounces5 Exposure Fill (preview)

How it was measured

Canvas	222.6 × 221.9 cm
Reference scale	0.232 cm / px
Horizon	row 400 of 963
Focal length	1800 px
Viewing distance	4.2 m
Eye height	1.10 m
Floor point depth	f · h / (row − horizon)

The rug is a rectangle turned about 21° from the walls, so its two edges give two vanishing points at columns −215 and 5200. For perpendicular edges, f² equals the product of their distances from the centre, which gives 1800 px. The horizon and eye height come from placing Mary Louisa (8) and the elder sisters at their plausible heights on the floor: the viewer's eye is about as low as a child's.

Checks that were not fitted

Tall vase	1.85 m
Julia's head (the toddler)	0.22 m
Rug, visible length	2.6 × 2.2 m
Left wall, behind Mary Louisa	0.9 m
Standing girls (set)	1.26 m, 1.5 m

The two standing heights were used to find the horizon, so they are assumptions, not tests. The vase and the toddler's head were not used, and both come out at believable sizes.

Confidence

Measured Floor positions of the four girls, the vases, the rug outline, the left wall line.

Inferred Camera height, focal length, the depth of the walls and alcove, the cabinet and the red door.

Invented Light positions other than the direction of the far-left window, the ceiling and anything outside the frame, hidden bodies, the room to the right of the red door.

Review note. The focal length assumes the picture's centre is the viewer's axis. If the axis sits further right, f rises (about 2000 px at column 700). The bright strip lines up with a wall at x = 1.0 m running from depth 8.1 m to the back corner, which is why the wall position is a slider. With a mirror flat on that wall, the sight line cannot reach a window far to the left of the room, so check how the far-left light is meant to be seen.