Visual Plane
every picture states the point it is correct from
Concept

Convolution — where it appears

Blurring by sliding one fixed shape along another and adding. It describes a defocused picture only where nothing occludes anything: at an edge the pupil sees round the occluder, so the result is not any function of the sharp picture at all.

Named by 3 essays across 2 fields — each of them below, with the objects they name alongside it.

the pupilan opaque edge120 mmf/1.4, focused at 6 m3 of 5 rays get past

A pupil sees around an edge

Two backgrounds identical everywhere a pinhole can see, differing only in the strip an occluder hides from it, produce identical pinhole pictures and pupil pictures 42 per cent apart. So no function of the sharp image — no kernel, no depth-dependent kernel, nothing — produces the picture a real lens makes, and the reach behind the edge is R(Z₂/Z₁ − 1), which is 120 mm here.

sensor · Aperture at one depth — a stadium, to 1.8e-5receding — tapered, 4% outone point, one exposure, the whole pupil1.8e-5 against 4%

The disc and the streak

A frame integrates over the pupil and over the exposure at once. Hold the point's depth and the patch is exactly the streak of its centres with one disc slid along it, to 1.8 × 10⁻⁵ of its own width. Let it recede over the same exposure and the disc's radius falls by 3.7 along the streak, and the patch departs from any single kernel by 16 pixels.

sensor · Aperture 00.2500.5000.7501-10-50510across the edge, in pixels of the picturehow much of the background reaches the sensorwhere a pinhole puts the edgethe pupilone depth per samplethe same edge, two ways of blurring it70% apart

One depth per sample is not enough

A depth buffer keeps a single distance at each sample, so a post-process blur can only ask how far away the thing at this pixel is. Across an occluding edge that answer is two depths and an occlusion, and the gather it produces differs from the pupil's own integral by 70 per cent of full scale over a band eleven pixels wide.

pipeline · Zbuffer

Named alongside it

The objects these essays reach for when they reach for this one.

ApertureCircle of confusionEntrance pupildepth of fieldIdentifiabilityinstrument limitMotion blurOcclusionSensorDepth bufferExit pupilExposure

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