How to use
- 1Upload a reference photo or a photo of your painting.
- 2In value-groups view, set the number of values from 2 (notan) to 9, or switch to plain grayscale.
- 3Use the squint slider to blur details away and see the big value masses.
- 4Compare side by side with the original and download the result as PNG.
Why values matter so much
Painters often say that if the values are right, the colour hardly matters. Value is how light or dark a colour is. Red and green can look completely different yet share the same value, which makes a painting look flat and muddled in a black-and-white photo. This tool calculates the perceptual lightness (CIELAB L*) of every pixel and shows the picture in values only.
Notan and value groups
Notan is a design study of Japanese origin that reduces an image to light and dark. Set the values to 2 for a notan, or to 3–5 for the simplified value plan most painters use when sketching. The percentages on the value scale show how much of the picture is dark, mid and light; a balanced composition usually lets one value dominate.
Squinting and comparing
Squinting removes detail and brings out the big shapes. The blur slider does the same on screen. Use the side-by-side view to compare the values of your reference with those of your painting. Everything happens in your browser; the image is not uploaded.
Frequently asked questions
What is a notan?
A notan is a two-value study that splits an image into black and white masses to show the balance of a composition. Set the number of values to 2 to get one.
How many values should I use when painting?
Three to five values are common for thumbnails and planning: dark, mid and light, plus a couple of in-between steps. More values help with detailed studies.
How is this different from a normal black-and-white filter?
Simple filters may just average the channels. This tool uses CIELAB L*, which is close to how the eye perceives lightness, and also groups values and shows the share of each group.
How do I check my finished painting?
Photograph it in daylight without glare and upload it. Turn on side-by-side and compare it with your reference at the same number of values.
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