How often should I check my values while painting?

Check at the moments when a value mistake is still cheap to fix: right after the block-in, after the first full pass of color over the whole surface, before you start on details, and once more before you call the painting finished. Between those, check whenever a passage starts to feel wrong and you cannot say why. Each check takes under a minute. Squint or step back for the quick ones, and use a grayscale view or a photo for the one before details, when the big shapes have to be settled.

Is squinting enough to check values?

Squinting is the fastest check and it catches most problems, because it blurs detail and leaves the big shapes of light and dark. It is less reliable for comparing two areas of very different color, since the eye keeps reading the colors even through half-closed eyes. When two passages look close and you need to know which is darker, confirm with a grayscale photo, a value scale card with punched holes, or a grayscale view in a painting app.

Why does my painting look different in black and white?

Because color hides value. A saturated orange and a dull blue-gray can look very different in color while sitting at almost the same lightness, so in black and white they merge into one gray. That merge is the information you were looking for: it shows where your light and dark shapes have stopped separating. Very saturated colors are the exception worth knowing. The eye sees them as brighter than a gray of the same measured luminance, an effect called the Helmholtz-Kohlrausch effect, so a grayscale check can make them look darker than they feel.

Can I keep painting while looking at a grayscale version?

Yes, and it is one of the most useful ways to fix values, because you adjust a passage and see its gray value change at the same moment. On paper or canvas you cannot do this directly, so you alternate between painting and checking a photo. In Trazu, the Values study view stays on while you paint, and the color picker and eyedropper show colors through the same view, so you can choose the next color by its value. The study views are part of Trazu Premium, a one-time purchase.

How to Check Your Values While You Paint

Q: Are red value filters accurate?

No, and they were never meant to be exact. A red filter makes a scene read closer to one color, which helps you compare values quickly, but it shifts the values themselves. As the landscape painter Michael Chesley Johnson notes, reds turn a little lighter, whites turn darker, and greens read much darker than they are. Use a red filter to compare big masses, never to judge a green against a red.

To check your values while you paint, stop at a few set moments and remove color or detail from your view: squint, step back, look at the painting in a mirror, or see it in grayscale. Then ask one question. Does the painting still read as a few clear groups of light, middle, and dark? Fix the biggest break first.

A value study before you start is the plan. If you have not made one, start with how to do a value study before you paint and how many values a study needs. This post is about what happens after the plan, when color goes on and the values start to drift.

Why values drift once you start painting

Values drift because color is persuasive and the eye judges everything by its neighbors. A study in gray makes value the only decision. Paint adds hue and saturation, and a passage that looks right in color can be a full step too light or too dark. You only see it later, when the whole painting reads flat.

Three things cause most of the drift:

Local color. A red shirt in shadow still looks like a red shirt to you, so you paint it red, and the shadow comes out lighter than the plan.
Close-up judgment. At brush distance you compare each stroke with the stroke next to it. Small, reasonable steps add up to a shadow that is now as light as the halftone.
Detail. Rendering a dark eye socket or a bright highlight breaks a big shape into small pieces, and the clean pattern of the study dissolves.

A value study cannot protect you from any of these, because they happen at hour two, not before the first stroke. That is why checking has to be a habit during the painting, not a single event before it.

The question to ask at every check

Every value check answers the same question: do the shapes still group the way you planned? Most painters plan in three to five groups. At each check, look for those groups, not for accuracy in any single spot.

Two comparisons find most problems:

The darkest light against the lightest shadow. Everything in the light should stay lighter than everything in the shadow. If a halftone in the light is now as dark as a reflected light in the shadow, the separation is gone, and the form goes soft. This is also the most common cause of shadows that look dirty, covered in why your shadows look muddy.
The focal area against everything else. The strongest contrast of light against dark should sit where you want the eye to land. If another area has an equally strong jump, it competes.

If both comparisons hold, leave the values alone and keep painting. A check that finds nothing is a good check.

Six ways to check values mid-painting

Each method below removes something from your view so value is easier to see. They differ in speed and in what they distort.

Squint

Squinting is the fastest value check. Half-close your eyes and the detail blurs, so you see the painting as big shapes of light and dark. The Painter’s Keys calls the squint a quick re-evaluation that “gives the artist a second opinion”, one that “lets you know where darkness or lightness might be added.” Squint at the painting and the subject or reference in turn, and compare the same shapes. Its weakness is color. You still see hue through half-closed eyes, so two areas of very different color are hard to rank.

Step back

Stepping back shows the whole painting at the size a viewer sees it. Leonardo da Vinci gave this advice in his notebooks, saying that it is good to move away from the work “because the work looks smaller and your eye takes in more of it at a glance and sees more easily the discords or disproportion in the limbs and colours of the objects” (The Notebooks of Leonardo da Vinci, translated by Jean Paul Richter). In the same passage he recommends leaving the work for a while, because sitting too close “may greatly deceive you.” Set a rule: step back every time you clean the brush.

Look in a mirror, or flip the image

A mirror makes your own painting look like someone else’s, and that is what lets you judge it. In the same notebook passage, Leonardo tells painters to keep a flat mirror and often look at the work in it, so that it “will appear to you like some other painter’s work, so you will be better able to judge of its faults than in any other way.” Your eye has memorized the painting and fills in what it expects. Reversed, it has to read the picture again, and a dark that is too heavy or a light that floats becomes obvious.

A darker variant of the same idea is the Claude glass, a small black convex mirror that eighteenth-century artists and landscape tourists used to reflect a view and make its tonal values and areas of light and shade visible. Any dark reflective surface, like a phone screen that is switched off, gives you a rough version of it.

Photograph it in black and white

A black and white photo removes color completely, which makes it the most direct value check on paper or canvas. Take the photo straight on, in the light you paint in, and turn it black and white in your phone’s photo editor.

Two cautions. First, the camera adjusts exposure and the screen adds its own brightness, so trust the relationships between areas, not the absolute lightness. Second, black and white conversions are not all the same recipe. The GIMP documentation on desaturating shows one image of a yellow sunflower converted several ways: the Lightness method renders it much darker than the Luminance method, which keeps the relative luminance of the original. If yellows look suspiciously dark in your gray photo, the conversion may be the reason, not your painting.

Use a value scale card

A gray scale card with a hole punched through each step lets you isolate one spot and match it. Hold it at arm’s length, look through a hole at an area of the painting, then at the same area of your subject, and compare each with the gray step around the hole. It is slow, so use it for the arguments squinting cannot settle, such as whether a sunlit wall or the sky behind it is lighter.

Look through a red filter

A red filter, sold as red acetate or value viewing glasses, makes everything read as shades of one color, so the big value masses separate fast. It also changes the values it shows. The landscape painter Michael Chesley Johnson, who keeps one in his plein air backpack, notes that reds turn a little lighter, whites turn darker, and greens read much darker. Use it to compare masses, never to judge a green field against a red barn.

When the gray check and your eye disagree

Sometimes a painting looks right in color and wrong in gray, and the gray check is not always the one telling the truth. Two cases matter.

The first is a real value problem hidden by color. Two areas look different because they differ in hue, but they sit at the same lightness, so in gray they merge. If those two areas were supposed to be different value groups, the gray check caught a mistake.

The second is deliberate. Claude Monet painted the orange sun in Impression, Sunrise at about the same luminance as the gray sky around it. The Harvard neurobiologist Margaret Livingstone points out that a black and white version makes the sun nearly disappear, and suggests this is why it can seem to pulse: the part of the visual system that reads position and motion sees no difference, as described in Harvard Magazine’s profile of her work. In that painting, the merge is the effect.

Very saturated colors add a third wrinkle. The eye sees a saturated color as brighter than a gray of the same luminance, an effect called the Helmholtz-Kohlrausch effect. A vivid red or blue can therefore look lighter in the painting than it does in any grayscale check.

The practical rule: use the gray check to protect the design, the big pattern of light and dark shapes. Where a merge in gray is a choice, like Monet’s sun, keep it. Where it is an accident, fix the value. When the values hold and the painting still feels wrong, the problem has moved to color, and the next places to look are warm and cool temperature and saturation.

When to check: a simple routine

Checks are cheapest early and most expensive at the end. A routine that works for most paintings:

After the block-in. The big shapes are on the surface. Squint and check the light against the shadow. This is the most important check, because everything after it is built on it.
After the first full pass of color. Every area now has paint. Take a black and white photo and compare it with your value study. Local color has usually pulled something out of its group by now.
Before details. Step back and look in a mirror. Detail is the last moment you can still move a whole shape without repainting finished work.
Before you call it done. Look at the painting fresh, after a break, in a mirror or flipped. Check that the focal area still holds the strongest contrast.

When a check finds several problems, fix the largest shape first. Correcting one big area often fixes three small ones, because the small ones were judged against it.

How to check values in a painting app

Digital painting removes most of the friction from value checks, because the grayscale view sits on top of the painting itself. In Trazu, the painting app from Paintingstack with wet, charged brushes and real paper grain, the study views live in a menu at the top of the canvas, showing Normal by default. Choose Values and the painting turns to grayscale, with each color’s lightness kept the way the eye ranks it, so a yellow stays light.

What makes it a check while you paint, rather than before:

You keep painting in the Values view. Adjust a shadow and watch its gray change with the stroke. No photo, no switching apps.
The color picker reads through the view. With Values on, the color disc and swatches in the color picker show as grays, so you can choose the next color by its value. Tap the study view chip at the top of the picker to peek at the true color.
The eyedropper does too. Its loupe shows the sampled color through the active view, so you can check the value of any spot you pick up.
Contrast widens the gap between lights and darks, which makes compressed middle values easy to spot when the painting feels gray but you cannot see where.
Flip horizontal, in the Canvas menu, mirrors the whole drawing for Leonardo’s check. Flip it again to set it back.

The same menu has Temperature and Saturation for the color checks that come after the values hold. One thing to know before you share: the drawing remembers the view you leave it in, and the exported image uses it, so switch back to Normal for a color export.

The free version of Trazu paints with the Normal view. The four study views, Values, Temperature, Saturation, and Contrast, are part of Trazu Premium, a one-time purchase with no subscription. If you are still deciding which app to paint in, see the best simple drawing and painting apps.

Check early, check the big shapes

The value study is where you plan the painting. The checks are how you keep it. Squint after the block-in, photograph it in gray after the first pass, look at it in a mirror before details, and every time ask whether the light and shadow groups still hold. Most failed paintings were fine at the start and drifted one reasonable stroke at a time.

Trazu is available on iPhone and iPad, Mac, and Android. No account, no ads, and your drawings stay on your device.