Levels and Curves for Exposure and Color – Classic Day 6

Control Highlights and Shadows

Levels and Curves are the two adjustment layers most photographers reach for first, and on the surface they look like they do the same thing. Largely, they do. Both let you define the darkest and brightest points in a photo, adjust exposure generally, and shift colour into the highlights and shadows. The difference is not what they can do — it is how much control the interface hands you.

Because both are adjustment layers, everything from Classic Day 4 applies: masks, opacity and blending modes all work on them, so any correction here can be confined to one part of the frame.

Read the Histogram First

Both dialogs show a histogram of the image, and it is worth a glance before you touch anything. It is a map of how much of the photo sits at each brightness level — darks on the left, brights on the right.

A stack piled against the left edge means most of the image is dark. A spike on the right means it is bright. Detail crushed hard against either end is information the file no longer holds, which tells you where you have room to work and where you do not.

The Levels Dialog

Levels gives you two rows of sliders, and the distinction between them is the thing most people never learn.

Input Levels

The upper set, sitting under the histogram. Drag the shadow slider right and everything to its left becomes pure black. Drag the highlight slider left and everything to its right becomes pure white. The midpoint between them lightens or darkens the middle values without moving either end.

This is how you set true black and white points, and it is what adds contrast — you are pulling the ends of the tonal range outward to meet the actual data in the image.

Output Levels

The lower set does the opposite, and it is the one people forget exists. Bringing the shadow output slider up lifts the darkest areas so they are no longer black. Bringing the highlight output slider down stops the brightest areas reaching white.

Input adds contrast; output removes it. That is the cleanest way to remember which is which, and lifted output shadows are the basis of most faded and matte looks.

Colour Channels

The dropdown at the top of the dialog switches from the combined RGB view to Red, Green or Blue on its own. Move the sliders in a single channel and you are pushing that colour into a specific part of the tonal range rather than across the whole picture.

The Curves Dialog

Curves shows the same histogram, but instead of sliders you get a straight diagonal line running from the bottom left to the top right. Left along the line is shadows, right is highlights, and the height of the line is brightness.

Adding Points

Click anywhere on the line to place a point, then drag it. Up makes that range of tones brighter, down makes it darker. The two ends of the line are the black and white points, and dragging them inward does exactly what the Levels input sliders do.

Why More Points Means More Control

This is where Curves pulls ahead. You can place as many points as you like, so you can brighten the midtones while holding the highlights in place with a second point — something Levels cannot do, because it only has one midpoint for the entire range.

The classic move is an S-curve: one point pulled down in the shadows, one pushed up in the highlights. It adds contrast without crushing either end.

Colour Channels in Curves

Same dropdown, same idea, more precision. Lift the blue channel in the shadows and only the dark areas go cool; pull it down in the highlights and the bright areas go warm. Doing both at once is a split tone in two moves.

Which One Should You Reach For

They edit the same information, so this is genuinely a matter of preference rather than capability.

Levels is faster and harder to get wrong. If the job is “set a black point, set a white point, brighten the middle”, it does that in three drags with no ambiguity. Curves is the better tool the moment you need to hold one part of the tonal range still while moving another. Most photographers end up using Levels for quick corrections and Curves for anything expressive.

Correcting a Photo Step by Step

1. Add the Adjustment Layer

   Layer > New Adjustment Layer > Levels or Curves, or use the half-dark circle icon at the bottom of the Layers panel.

2. Set the Black and White Points

   Bring the input shadow and highlight sliders in until they meet where the histogram data actually begins. Do not overshoot — past that point you are deleting detail.

3. Adjust the Midtones

   Move the Levels midpoint, or place a point in the middle of the Curves line, until the overall brightness reads right.

4. Work Per Channel if the Colour Is Off

   Switch to Red, Green or Blue and correct a cast where it actually lives — a blue cast in the shadows is fixed in the blue channel’s shadow end, not with a global warming filter.

5. Mask It Where It Belongs

   If the correction only suits part of the frame, press Ctrl/Cmd + I to invert the layer mask to black, then paint white with a soft, low-opacity brush over the area that needed it.

Combine Them With Everything Else

Because these are ordinary layers, the rest of the toolkit applies. Drop the opacity to ease off a correction that is right in character but too strong. Set the layer to Luminosity so a contrast change does not shift your colours. Stack several, each masked to a different region, rather than trying to solve the whole photo with one.

And nothing is permanent — click the adjustment layer at any point to reopen it and move the sliders again. Classic Day 3 covers masks if that part is still new.

Practise on the Sample Image

Download the sample and try the same photo twice — once corrected entirely with Levels, once entirely with Curves. Set the black and white points, lift the midtones, then colour tone by moving one channel in the shadows and the opposite way in the highlights. Comparing the two is the fastest way to work out which dialog suits how you think.

Tomorrow, Classic Day 7 targets individual colours with Hue/Saturation. Colour grading in depth is Classic Day 20. For the current comparison of these two tools, see Day 7 of the 2025 Edition.

Related Tutorials

• Match Color in Photoshop: 4 Easy Steps With Levels
• Correct Color and Exposure in Photoshop: 5 Easy Steps
• Levels vs Curves in Photoshop: 1 Simple Difference