What Are Tone Curves and How Do You Use Them on iPhone
Tone curves are advanced adjustment tools that let you reshape the tonal range of a photo by pulling specific points along a diagonal line, giving you precise control over highlights, midtones, and shadows on your iPhone. Cleanr by MRVL includes tone curves in its AI Pro tier, letting you make pro-level edits without learning desktop software.
What tone curves actually do
A tone curve is a graph where the horizontal axis represents the input brightness of your photo (from black on the left to white on the right) and the vertical axis shows the output brightness after adjustment. When you pull a point on the curve upward, you brighten those tones; pull downward and you darken them. The diagonal line in the middle is the default state, unchanged. By placing multiple points along the curve and adjusting them, you can brighten shadows while keeping highlights the same, or crush blacks while lifting midtones for that cinematic look. Unlike simple brightness sliders, curves give you granular control over which tonal zones of your photo get adjusted.
Common tone curve adjustments on iPhone
Most iPhone photographers use tone curves for three main edits. An S-curve (pulling shadows down and highlights up) increases contrast dramatically, making dark areas darker and bright areas brighter for that snappy, professional finish. An inverted S-curve does the opposite, flattening contrast for a soft, moody aesthetic. Lifting just the shadow area of the curve (bottom left) brightens underexposed areas without blowing out the sky. A steep curve in the midtones region adds punch to skin tones or product photos. Cleanr's curves tool uses catmull-rom spline interpolation, which means your adjustments stay smooth and natural across the entire tonal range, not jarring or posterised.
How to use tone curves in Cleanr
Open a photo in Cleanr by MRVL and tap the Adjustments menu. If you're on the free or Plus tier, you'll see standard sliders like brightness and contrast. To access tone curves, upgrade to the AI Pro tier (£12.99 per month or £99.99 per year). Once activated, the curves interface appears as a diagonal line overlaid on a histogram of your photo's tones. Tap anywhere on the curve to add a control point, then drag it up to brighten that tonal range or down to darken it. You can add up to 10 points along a single curve. The preview updates in real-time as you adjust, so you see the effect instantly on your photo. Remove a point by dragging it off the curve entirely.
Tone curves vs. simple brightness and contrast sliders
Basic brightness and contrast sliders affect the entire image uniformly. Moving brightness up lifts every tone equally. Contrast affects every tone proportionally. Tone curves, by contrast, let you isolate specific zones. You might brighten shadows to reveal detail in dark corners while leaving highlights completely untouched. You can also create looks impossible with sliders alone, like lifting only the darkest blacks while keeping midtones flat, or brightening the brightest skies while darkening everything else. If you're only doing occasional photo tidying, sliders are usually enough. If you're editing regularly for social media or product photography, curves unlock a professional level of control that separates casual edits from polished ones.
When to use tone curves for iPhone photos
Tone curves shine when your photo's tonal distribution is uneven. A landscape shot with a blown-out sky and dark foreground is perfect for curves, because you can darken just the bright sky without touching the landscape. Portraits with harsh shadows benefit from lifting the shadow areas while keeping skin tones in the midtones intact. Product photos on a white background often need curves to brighten the background without washing out the product itself. Night photos shot in low light often have crushed blacks; a gentle curve that lifts the shadow region reveals detail without making the photo look flat. Cleanr also includes selective adjust, a brush-based tool in the AI Pro tier, so you can apply tone curve adjustments to specific areas of your photo rather than the whole image.
Getting started with Cleanr on iPhone
Cleanr is available on iOS and Android. The free tier includes auto-enhance and basic adjustments (brightness, contrast, saturation, warmth, sharpness) plus three enhancements per day with no watermark. If you want unlimited tone curve access along with HSL colour controls, face retouch, generative fill, and selective brush adjustments, the AI Pro tier costs £12.99 per month or £99.99 per year. There's also a Core Lifetime licence for £4.99 that covers the app's core toolkit forever, ideal if you want one-time payment simplicity. All paid tiers unlock HD export and commercial licence rights, so you can edit photos for client work or e-commerce without licensing concerns.
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Frequently asked questions
What is a tone curve in simple terms
A tone curve is an adjustable line that lets you brighten or darken specific zones of your photo, like shadows or highlights, independently. It's more precise than a single brightness slider because you control exactly which tones change.
Can I use tone curves on iPhone without an app
iOS's built-in Photos app does not include tone curves. Specialised photo editors like Cleanr by MRVL, Lightroom Mobile, or Snapseed offer curve tools. Lightroom's curves are industry-standard but require a subscription; Cleanr's curves are available in the AI Pro tier.
How do I know if I'm using tone curves correctly
If your photo looks more contrasty, brighter in shadows, or has a cinematic feel after adjusting the curve, you're on track. Start by creating a gentle S-curve and preview the result. If the photo looks unnatural or overly processed, undo and use a subtler curve with fewer control points.
Is the tone curve tool free in Cleanr
Tone curves are included in Cleanr's AI Pro tier (£12.99/month or £99.99/year). The free tier includes basic sliders; the Plus tier (£3.99/month or £29.99/year) adds unlimited access to core tools but not curves, HSL, or selective adjust.
Can I undo tone curve adjustments in Cleanr
Yes. Cleanr stores a full edit history on the Plus and Pro tiers, so you can revert any adjustment or return to the original photo at any time. The free tier lets you undo the most recent edit.
What is the difference between a curve and HSL adjustments
Tone curves adjust brightness across tonal ranges (shadows, midtones, highlights). HSL adjustments (Hue, Saturation, Lightness) let you target specific colours instead, so you can brighten only the reds or desaturate only the blues. Cleanr includes both in the AI Pro tier.