What does a value checker show?
It shows how light or dark each part of your picture is, with the colour taken away. Value carries most of what reads from across a room: the big shapes, where the light falls and what the eye goes to first. A painting with a muddled value structure often still looks muddled in good colour, and grayscale is the quickest way to see that.
The tool gives you two ways to look:
- Gray is a straight grayscale. Use it to spot small slips, like a shadow that is lighter than the lit side next to it.
- 2 to 5 values groups every pixel into that many tones, evenly spaced from black to white. Use it to see the design: which shapes join, which separate, and whether the darks and lights are grouped.
The bars under the histogram show what share of the picture falls in each value, so you can see at a glance whether a “mostly light” painting really is.
How is the grayscale worked out?
Each pixel’s lightness is CIE L*, from 0 (black) to 100 (white), computed from its relative luminance Y = 0.2126 R + 0.7152 G + 0.0722 B on linear sRGB. Those weights are the Rec. 709 ones that WCAG uses for relative luminance, and L* is the CIELAB lightness scale, built so equal numeric steps look like equal steps of lightness.
The choice matters. Quick ways of removing colour, like averaging the three channels or taking HSL lightness, rate colours very differently from how bright they look:
| Colour (sRGB) | L* used here | HSL lightness | Average of R, G, B |
|---|---|---|---|
| Yellow #FFFF00 | 97 | 50% | 67% |
| Cyan #00FFFF | 91 | 50% | 67% |
| Green #00FF00 | 88 | 50% | 33% |
| Orange #FF8000 | 67 | 50% | 50% |
| Magenta #FF00FF | 60 | 50% | 67% |
| Red #FF0000 | 53 | 50% | 33% |
| Blue #0000FF | 32 | 50% | 33% |
These figures are computed by the tool’s own code and checked in its tests. HSL lightness puts all seven colours at the same value, which is exactly the trap a value check is meant to catch.
Where should the thresholds go?
Start with the even split, then move the lines until the shapes read the way you intend. Each threshold is a lightness number from 1 to 99: everything darker than the first line becomes the darkest value, and so on up. With 3 values the even split is at 33 and 67; with 5 values it is at 20, 40, 60 and 80.
Equal areas moves the lines so each value covers about the same share of the picture. It is useful on a low-contrast photo where the even split puts almost everything in one band, and as a contrast to a deliberate design where one value should dominate.
The values in the result are evenly spaced in L*: with 3 values they are black, middle gray (sRGB 119, which is L* 50) and white.
Why squint and flip a painting?
Squinting blurs away edges and texture so only the large masses of light and dark remain, which is what the composition stands on. The squint slider does this with a Gaussian-like blur before the values are worked out, scaled to the image so the preview and the download match.
Flipping horizontally is an old studio check: after hours of looking at a piece your eye stops seeing its faults, and a mirrored view makes drawing and balance problems jump out. It works on the colour view too.
What do the downloads contain?
| Download | What is in it |
|---|---|
| PNG | The value map at your image’s full size: grayscale or your chosen values, with the squint blur, transparency kept |
| PSD | Two layers: your image as Colour, and the value map above it in the Luminosity blend mode |
In the PSD, hide the value map layer to see the colour, show it to see your colours forced onto the chosen values, or set it to Normal to see plain gray. The file stores both layers and the Luminosity mode, and Procreate’s handbook says its PSD import keeps layer blend modes. Images up to 30,000 pixels on a side are saved as PSD; larger ones are saved as PSB, Photoshop’s large document format.
Downloads are made at full size in the background. On a phone, very large images may be too big for the browser’s memory; the preview always works because it uses a copy no larger than 1,200 pixels.
How does it compare with other value tools?
Several free value and notan tools exist, and they do overlapping jobs. Checked on 2026-10-16:
| Tool | Values | Blur | Flip | Histogram thresholds | Output | Uploads |
|---|---|---|---|---|---|---|
| This page | Gray, 2 to 5 | Yes | Yes | Yes, draggable | PNG, layered PSD | No |
| LlamaGen Value Study Maker | 2 to 9 | Yes | Yes | Not listed | PNG | No, per its page |
| Draw Paint Academy Notan Tool | 2 (one threshold) | Yes | Not listed | No | Image download, desktop only | Not stated |
| Photoshop or Procreate | Any, by hand | Yes | Yes | Photoshop’s Threshold and Levels show one | Native file | No |
If you need more than 5 values, LlamaGen’s tool goes to 9. If you already work in Photoshop or Procreate, a gray layer in Color mode at the top of your layer stack is a live check that updates as you paint, which this page cannot do.
What it doesn’t do
It doesn’t critique or correct a painting, find the focal point, or simplify shapes the way a painter would; it measures lightness and groups it. It reads one image at a time, and it doesn’t open .procreate or .psd files directly. For a Procreate file, get a flat PNG with the Procreate to PNG tool first, then drop the PNG here.