Previously, I posted an explanation of the different sliders available with the adjustment brush. I’ve had a few questions come in asking for more clarification about the difference between the flow and density sliders in Lightroom so, in this post, I’ll talk about each more in depth.
Flow, as it sounds, controls the speed at which the adjustment is applied to your image when painting with the brush. When your flow is at 100, the effect from the adjustment brush happens very quickly; one stroke of the brush applies the full effect. With a lower flow, it will take longer for the effect to be completely applied. That’s a handy tool when you’re trying to slowly apply and control the effect on an image.
I’ve seen other tutorials suggest that with a flow of 50 that you can reach the full effect by painting over an area twice, but in practice, I’m not sure that’s true based on how the effect i actually applied. Check out the illustration below. Two brush strokes do not achieve the full effect, at least not consistently. I needed to make multiple passes at 50% flow to get the full effect.
Try it yourself. On an image, set the exposure to -4 and the flow to 50. Without moving the mouse, click once to apply the effect. With each click, it should darken. After about 12 clicks, it was hard to distinguish from the 100% flow.
Density, however, puts a cap on how much of an effect is applied. A density value of 50 caps the effect at 50%. For example, if your effect applies a +2 exposure, a 50% density means that, no matter how long you paint the effect, it will never get more of a change than a +1. The example below shows a 100% density adjustment of a -2 exposure, a 50% density adjustment with the same exposure value, and a -1 exposure applied with 100% density. The last two should be, and are, identical.
So why use density at all? Why not just adjust the sliders to match the target effect? That’s a great question! If you’re just messing with the exposure or a single adjustment, it’s probably easy enough to do just that. However, if you’re applying a combination of adjustments with your brush and you want to apply a lighter touch to one piece of an image, instead of trying to figure out the right rations to adjust all the sliders, you can simply adjust the one density slider and soften the effect. When you move to another section of the image that can take a harder adjustment, you can simply move the density slider back up.
Combining Flow And Density
The more comfortable you get with using both sliders, the more you’re likely to use them to in your workflow. The ultimate in brush control comes from combining the flow and density sliders to both control the rate at which an effect is applied and to limit its impact on an image. The adjustment brush is one of the most powerful ways to take your image from good to great by isolating adjustments to where they are needed. Mastery of the adjustment brush and effectively and efficiently using it as a part of your workflow will help you get the most out of Lightroom.