Tool · 21-step test chart
Free 21-step test chart, ready to print.
A 21-step test chart you can download freely, in high-resolution PNG and PDF. The digital equivalent of the Stouffer 21 step, usable with any densitometer or visual reading. No sign-up.
Génère ta mire 21 steps (Stouffer compatible) maintenant
Mire 21 patchs (grille 3×7 + dégradé continu), paliers d'environ 5.0 % d'intensité, échelle L* CIELAB. Choisis ta polarité ci-dessous, télécharge, imprime sur transparent jet d'encre sans gestion de couleur, insole sur ton papier sensibilisé.
Version téléchargée en 1680×1410 px, adaptée à un tirage standard. Pour des dimensions et un nombre de patchs personnalisés, utilise la fonction mire sur mesure de l'app, débloquée avec le code Luminograph.
Mire générée par le même algorithme que l'app (fonction generateSingleMire). Échelle de mesure : luminance perceptuelle L* CIELAB.
Download
Two formats — PNG or PDF.
PNG format
21-step chart — PNG 4800×1200 px
Greyscale 16-bit, watermark included. Suitable for inkjet printing on film or transparent paper.
Download the PNGPDF format · coming
21-step chart — A4 PDF
A4 layout with 5 mm margins and crop marks, watermark included. The PDF generator is not connected yet; in the meantime, use the high-resolution PNG and print it from Photoshop or Preview without colour management.
Coming soonWatermark: "Generated with Calibration Flow"
Format choice
Why 21 steps, and not 25?
Calibration Flow uses a 25-patch chart (5×5 grid, ~4% steps) in the app, optimised for smartphone reading and L* CIELAB analysis. This 21-step chart is the generic compatible version: it matches exactly the historical Stouffer 21 step format, the reference scale of labs since the 1980s.
21 steps is a compromise between granularity and visual legibility. Each step represents about 0.15 optical density, or half a stop. That is enough to visually identify the shadow and highlight bounds of a process.
If you want a numerical calibration with automatic L* reading and .acv export, the interactive 25-patch chart of the Calibration Flow app is more precise. If you want a paper chart to print and read visually or with a densitometer, this one fits.
Usage
How to use this chart
- 1
Print without colour management
Print the PNG or PDF in greyscale, with no ICC profile applied, on transparent film or diffusing paper. Any software correction skews the reference linearity.
- 2
Expose on your sensitised paper
Place the chart on the sensitised paper, expose under your UV source. Note your parameters — time, distance, source — to reproduce.
- 3
Read the bounds
Identify the first visible step (practical Dmin) and the last step distinct from black (practical Dmax). You get the usable tonal range of your process.
25 patches, L* reading, exported curve.
The interactive 25-patch chart of Calibration Flow is generated at your paper size and read automatically by smartphone. Free with sign-up on Web, no credit card.
Calibrate with the interactive 25-patch chart