How to use the Notan & Value Study Tool
- Open a reference. Click Open a reference, drop a photo on it or paste one from the clipboard. The built-in landscape is there so you can try every control first. Your image is processed on your own device and never uploaded.
- Choose how many values. 2 · notan splits the picture into dark and light shapes; 3, 4 and 5 add middle tones. The study appears next to the original, or on its own with the View buttons.
- Set the thresholds. Each handle on the histogram is a cut between two values. Drag it, click anywhere on the histogram to pull the nearest handle there, or focus a handle and use the arrow keys (hold Shift for steps of 5). Auto finds the split the image suggests; Even steps divides the lightness scale equally.
- Simplify the shapes. Move Simplify shapes up to merge leaves, grass and texture into bigger masses, the way half-closed eyes do. Press and hold the study to flash the original under it.
- Pick value colors and export. Choose Grays, Band average, Sepia, Payne’s gray, or click a swatch to set any color for that value. Download PNG saves the study at the working resolution, Side-by-side PNG adds the original and a labeled key, and Copy value key copies the HEX codes and area percentages.
Why a value plan comes before color
Value is how light or dark a color is, and it carries most of a picture’s structure. If the big shapes read clearly in two or three values, the painting will hold together at thumbnail size, across a room and in a black-and-white print. If they don’t, no color choice will rescue it. The Japanese term notan names this arrangement of dark and light, and Arthur Wesley Dow made it a core exercise of American art teaching in his 1899 book Composition.
The catch is that the eye is bad at judging the value of saturated colors, and so are many quick grayscale filters. A simple average of red, green and blue scores pure red #FF0000 and pure green #00FF00 identically, at 85 out of 255. Perceptually they are far apart: red has a CIE L lightness of 53, green 88. Pure yellow #FFFF00 reaches L 97 while pure blue #0000FF sits at 32. This tool converts every pixel to L*, the scale designed so that equal steps look like equal changes in lightness, so a yellow flower stays light in the study and a blue shadow stays dark.
One consequence surprises people: perceptual middle gray, L 50, is #777777, not #808080. The “obvious” halfway gray is actually L 53.6, a little light.
Choosing two, three, four or five values
| Values | Even-step cuts (L*) | Default grays | Best for |
|---|---|---|---|
| 2 | 50 | #1F1F1F, #F1F1F1 |
Notan design, poster and logo ideas, checking the big pattern |
| 3 | 33.3, 66.7 | #1F1F1F, #848484, #F1F1F1 |
Plein-air thumbnails: shadow, half-tone, light |
| 4 | 25, 50, 75 | adds #5E5E5E and #A6A6A6 |
Separating a dark middle from cast shadow |
| 5 | 20, 40, 60, 80 | #1F1F1F to #F1F1F1 in five steps |
Planning a full tonal painting or a grisaille |
Even steps are predictable, but real scenes rarely spread their values evenly. Auto uses a multi-level version of Otsu’s method from image processing: it tries every possible set of cuts and keeps the one that makes each group of pixels as internally similar, and the groups as different from each other, as possible. On the sample landscape it puts the notan split at L 50 and leaves 36% of the picture dark, which matches the tree, hills and foreground. At three values it moves the cuts to L 44 and 70.5, which separates the glowing horizon and lake from the middle-value upper sky and distant hills. Use Auto as a starting point and then drag the handles to say what you want the picture to be about.
The percentages under the histogram are the area each value covers. They are worth reading: a design where dark and light each take about half the picture often feels static, while a clear majority of one value gives the eye somewhere to rest.
Tips from practice
Simplify first, then set thresholds. Every leaf and pebble becomes a speck of the wrong value when you threshold a detailed photo. Raise Simplify shapes until the specks merge into masses, then fine-tune the cuts. The slider works on a median filter, so it keeps edges between big shapes crisp while it removes small ones.
Decide which middle tones join the darks. In a three-value study the middle band is where decisions happen. Dragging the lower handle up pushes the half-tones into shadow and gives you a bold, graphic design; dragging it down hands them to the light side and gives you an airy, high-key one.
Watch out for phone-camera shadows. Phones often crush shadows to near black and blow out skies. If a whole area turns into one flat dark shape, lift the threshold a few points or brighten the photo before you study it. Your eye on location saw more than the sensor did.
Turn the key into paint. Click Copy value key, then mix a pile of paint for each value and check it against the swatch with a gray card or your phone’s camera. Custom value colors let you plan the study straight in a limited palette, for example burnt umber for darks, yellow ochre for middles and white for lights.
Check the drawing, not just the photo. Once the study works, compare your own drawing in the Reference Flip & Grayscale Tool: its grayscale and squint modes show whether your painting kept the same value pattern.