# Measure on a grid

> Judge a shape on a millimetre grid, never by eye. The iris is the ruler: it is close to 11.8 mm across in everyone, so it gives the scale of any photograph of an eye.

- URL: https://www.kiruk.in/making/grid-measure
- Kind: Pattern
- Made: Oct 2026
- Author: Arun Kumaar Sreenivasan
- Part of: How this was made (https://www.kiruk.in/making)
- Agent file: https://www.kiruk.in/making/grid-measure/agent.md

## The problem

A render can be wrong in a way nobody can name. Reviews said "robotic" and "too perfect". Looking harder did not help, because the eye that judges a face is the same eye that is fooled by one.

## The move

It is the grid method painters use to copy a portrait, with one change. The subject carries its own ruler.

1. Find the iris

   In the photograph and in the render. Its width in pixels, divided by 11.8, is pixels per millimetre.

2. Lay the grid

   Crop both to the same scale and lay a 1 mm grid over each, centred on the iris.

3. Read the numbers

   How far each corner sits below the centre, and how tall the opening is at 1, 2, 4 and 6 mm from the corner.

4. Fit the twin

   Fit the plain TypeScript copy of the lid curves to those numbers, and test it.

5. **Change the shader**

   Only now.

## What it found

Both corners of the photographed eye sit below the centre of the iris, the inner by about 3 mm and the outer by about 1.9. The render's inner corner was 0.9 mm low. Three millimetres against less than one: a difference too small to see as a number and large enough to feel as a stranger.

## When not to use it

For light. A grid measures shape. Whether skin looks alive under a green tube is still a judgement, made by looking.

## Lineage

### Came from

- [My own eye](https://www.kiruk.in/making/real-eye-photo) (Source, 20 Oct 2026): A macro photograph of my own eye replaced every other reference. From then on the question was no longer whether the render looked like an eye, but whether it looked like this one.

### Used by

- [The loader eye](https://www.kiruk.in/making/loader-eye) (Interface, May to Nov 2026): One human eye, drawn live in the browser and lit only by the screen it is looking at. It was built four times in six months, measured against a photograph of my own eye, and it changes era by blinking.