The Difference Between Flow and Opacity in Photoshop

Flow and opacity are two brush settings that look similar but behave in completely different ways once a brush actually touches a layer. This tutorial breaks down how each setting builds up color differently, shows how to switch between them with keyboard shortcuts, and applies the difference to a practical dodging and burning example.

Understanding the Basic Difference Between Flow and Opacity

Flow and opacity are both brush settings found at the top of the options bar, and while they can look interchangeable at first glance, they control buildup in fundamentally different ways.

1. Locate Opacity and Flow in the Options Bar

   With the Brush tool selected, find the Opacity and Flow settings at the top of the screen, both set to 100% by default.

2. Select a Black Foreground Color

   Choose black as the foreground color to make buildup easy to see against a light layer.

How Opacity Works Like a Computer-Generated Limit

Opacity behaves like painting with half a pen of ink: no matter how many times the same spot is painted over in a single stroke, the result never gets darker than the opacity setting allows.

3. Lower Opacity to 50%

   Press the number 5 on the keyboard to bring brush opacity down to 50%.

4. Paint Over the Same Area Repeatedly

   Paint back and forth over one spot and notice the color never gets darker than 50%, no matter how many passes are made.

5. Release and Paint Again to Add More

   Lift the mouse or stylus, then paint over the same area again to lay down another 50%, visibly stacking where the two strokes overlap.

Why Opacity Creates a Visible, Stacked Look

Because opacity locks in a fixed maximum for a single continuous stroke, building up more color requires lifting the brush and starting a new stroke each time. That start-and-stop process is what creates the visibly overlapping, less natural edges seen when two 50% opacity strokes stack on top of each other.

How Flow Works Like a Natural Marker

Flow behaves much more like an actual marker on paper: going over the same spot again within one continuous stroke keeps adding more ink instead of stopping at a fixed ceiling.

6. Reset Opacity to 100%

   Press 0 to bring brush opacity back up to 100% before testing flow.

7. Lower Flow to 10%

   Hold Shift and press 1 to bring flow down to 10%.

8. Paint Over the Same Area Repeatedly

   Paint back and forth over one spot and watch the color gradually darken further with each additional pass, building all the way up toward full black.

Setting Opacity and Flow With Keyboard Shortcuts

The number keys 1 through 0 control brush opacity, while holding Shift and pressing those same keys controls flow instead, making it fast to switch between the two while painting.

9. Press a Number Key for Opacity

   Press any number from 1 through 0 to set brush opacity to that value in increments of 10%, with 0 meaning 100%.

10. Hold Shift and Press a Number Key for Flow

    Hold Shift and press a number from 1 through 0 to set flow to that same increment instead of opacity.

Combining Flow and Opacity for a Capped Buildup

Setting a low flow alongside a reduced opacity allows color to build up gradually within a single stroke, but only up to whatever ceiling the opacity value sets.

11. Set Flow to 10% and Opacity to 50%

    Keep flow at 10% and press 5 to bring opacity down to 50%.

12. Paint to Build Up to the Opacity Ceiling

    Paint over the same area repeatedly and notice the color builds up gradually with flow, but stops once it reaches the 50% opacity ceiling rather than reaching full black.

13. Release and Paint Again to Push Further

    Lift the brush and start a new stroke to push the buildup past that 50% ceiling and continue darkening the area.

Why Combining Flow and Opacity Adds Extra Control

Using flow and opacity together makes it possible to build an effect up gradually and naturally within a stroke, while still capping how far any single stroke can go. That combination is what allows for careful, controlled buildup on areas where going all the way to full black or full white in one pass would be too aggressive.

Applying Flow to Dodging and Burning

A new layer set to Soft Light blend mode, painted with black or white, is a simple way to darken or lighten specific areas of a photo, and flow is what makes that painting process controllable.

14. Create a New Layer Set to Soft Light

    Add a new layer and change its blend mode from Normal to Soft Light.

15. Paint Black to Darken an Area

    Paint black directly over a shadow area to make it slightly darker, achieving the same effect as burning.

16. Paint White to Lighten an Area

    Paint white over a highlight area to make it slightly lighter, achieving the same effect as dodging.

Building Up Dodge and Burn Effects With Low Flow

Setting opacity to 100% but flow to a low value lets a highlight or shadow build up exactly where needed, without the repeated clicking and stacking that opacity-only painting would require.

17. Set Opacity to 100% and Flow to 10%

    Bring opacity back to 100% and hold Shift and press 1 to bring flow down to 10%.

18. Paint Over the Highlight Repeatedly

    Paint over an area like the top of a leg repeatedly with white to concentrate a highlight exactly where it should be strongest.

19. Switch to Black for the Shadow Side

    Press X to switch the foreground color to black, then paint over the opposite side to build up a matching shadow.

Why Low Flow Beats Opacity for Dodging and Burning

Painting a highlight or shadow with reduced opacity instead of flow means clicking, releasing, and clicking again over and over to build up enough effect, which is both tedious and prone to visible stacking. Using a low flow setting instead allows continuous painting directly over the area, concentrating the effect naturally wherever the brush spends the most time.

Understanding Brush Opacity Versus Layer Opacity

Brush opacity and layer opacity are two separate, independent controls, and the layer’s own opacity always has the final say over how the finished painting appears.

20. Finish Painting at Full Brush Opacity

    Complete the dodge and burn painting with brush opacity set to 100%, even if the result looks too strong.

21. Lower the Layer’s Opacity Afterward

    Reduce the opacity of the entire layer in the Layers panel to soften the overall dodge and burn effect.

Why Layer Opacity Overrides Brush Opacity

The brush’s own opacity setting only controls how paint is applied while actively painting on a layer, but it has no effect on the layer once that painting is finished. The layer’s opacity acts as the master control afterward, meaning a layer’s overall strength can always be adjusted later regardless of what opacity or flow was used to paint it.

Why This Approach Works

Flow and opacity behave differently because they solve different problems: flow mimics the natural buildup of a real marker, while opacity behaves like a fixed ceiling that requires lifting the brush to exceed. Combining the two, rather than relying on just one, is what makes it possible to build an effect up naturally while still keeping a hard limit on how far any single stroke can go. Keeping brush opacity and layer opacity separate in mind is what allows a finished dodge and burn layer to always be fine-tuned afterward, no matter how it was originally painted.

Final Thoughts

Flow and opacity might look like nearly identical settings sitting side by side in the options bar, but understanding how each one actually builds up color changes how confidently the brush tool can be used for retouching, painting, and especially dodging and burning. Once the difference feels natural, switching between the two with keyboard shortcuts becomes second nature during everyday editing.

Quick Reference: Keys, Menus and Settings

• Find the settingsBrush tool, options bar: Opacity and Flow (both 100% by default)
• Set opacity1 to 0: 5 is 50%, 0 is 100%
• Set flowShift + 1 to 0: Shift + 1 is 10%
• Dodge and burn layerNew layer, blend mode Normal to Soft Light; white lightens, black darkens
• Build it upOpacity 100%, Flow 10%, paint over the same area again and again
• Swap white and blackX
• Soften the resultLower the layer opacity in the Layers panel