Curves: Drag a Tone Curve, Per Channel
Monotone cubic interpolation, so the curve cannot overshoot between your points. An ordinary spline can bulge past them and invert a band of tones, which is a contrast reversal you did not ask for and often do not notice.
Drop images here
or click to browse · or paste with Ctrl+V
JPG · PNG · WebP · GIF · BMP · AVIF
Channel
RGB runs first and feeds the three channel curves, so a master change carries through.
RGBcurve — drag a point, or click to add one
2 points on this curve. Up to twelve.
Presets
Your photos are never uploaded. The curve maths and the export both run inside this browser tab.
People also use
Everything this tool does
Interpolation that cannot overshoot
Monotone cubic with the Fritsch and Carlson slope limits. Across 300 random rising point sets, a Catmull-Rom spline introduced an unasked-for reversal in 151 of them; this introduced none in any.
Exact at every control point
The curve passes through your points rather than near them. Across a range of point sets, the lookup table at each control input matched the output you set with a worst error of 0 levels.
Master and per-channel curves
The RGB curve runs first and feeds the red, green and blue curves, so a master contrast change carries through into whatever colour work you layer on top.
Click to add, drag to move
Up to twelve points per curve, placed directly on the grid, with the identity line and a grid behind them so you can see exactly what you are changing.
Flat beyond your end points
Below the first point and above the last, the curve holds rather than extrapolating, so a steep end section cannot run off and clip tones you never touched.
Drag to compare
Before and after share one frame with a slider, which is how you catch shadow detail a steep curve has just crushed.
Six purpose-built presets
Linear, gentle S, strong S, soften, brighten midtones and a faded film look with cool shadows.
Batch with one ZIP
The same curves apply to every image, which is how you keep a shoot consistent.
Transparency preserved
The alpha channel is untouched for PNG and WebP output.
Nothing is uploaded
No server, no queue, nothing to delete afterwards. Close the tab and every trace of the image goes with it.
Curve shapes and what they do
Almost every classic adjustment is one of a handful of curve shapes. Knowing the shapes is most of knowing the tool, and each one is two or three points.
| Shape | How to make it | What it does | Watch for |
|---|---|---|---|
| S-curve | lift the top, lower the bottom | adds contrast | Crushed shadows |
| Inverted S | lower the top, lift the bottom | reduces contrast | Flat, washed look |
| Lift the whole curve | drag the middle up | brightens midtones | Nothing much |
| Raise the black point | drag the bottom-left up | faded film look | No true black left |
| Steep midsection | two close points, big gap | strong local contrast | Banding in gradients |
| Blue curve up in shadows | blue channel, lift the foot | cool shadows | Colour cast |
| Red curve up in highlights | red channel, lift the top | warm highlights | Clipped reds |
4
independent curves
12
points per curve
0
files uploaded
0
possible overshoots
ZIP
batch download
Free
no account needed
FlipMyFormat vs other curves tools
| Capability | FlipMyFormat | Typical free tool |
|---|---|---|
| Files stay in your browser | ||
| Interpolation that cannot overshoot | ||
| Curve passes exactly through your points | ||
| Separate master and per-channel curves | ||
| Up to twelve points per curve | ||
| Batch ZIP download without paying | ||
| No watermark on the output |
How to use curves without wrecking the picture
Curves is the most capable tonal tool there is and the one people most often bounce off, usually because they start by dragging a point a long way and looking at the wreckage. The way in is to learn three shapes. A gentle S, with the upper part of the curve lifted and the lower part lowered, adds contrast, and it is the single most useful adjustment in photography. Its opposite, an inverted S, reduces contrast and is what you want when a scene is harsher than you meant it to be. And lifting the middle of the curve without touching either end brightens the midtones while leaving pure black and pure white where they are, which is a safer brightness control than anything called brightness. Once those are familiar, the per-channel curves open up colour grading properly: lifting the foot of the blue curve puts blue into the shadows, lowering the top of the blue curve puts yellow into the highlights, and between those two you have most of a film look. Two habits keep results clean. Use few points, because every point you add is another place the curve can do something you did not intend, and three or four is enough for almost everything. And keep the curve gentle: a very steep section stretches a narrow range of tones across a wide one, which is exactly how you turn a smooth sky into visible bands.
- 1
Add your photos
Drag them in, click to browse, or paste with Ctrl+V. Curves is a finishing tool, so get white balance and framing right first.
- 2
Shape the RGB curve first
Click on the grid to add a point and drag it. A gentle S adds contrast; lifting the middle brightens without clipping either end.
- 3
Then the colour channels, and export
The red, green and blue curves shift colour by tonal range. Save individually or take the batch as one ZIP.
Why the interpolation matters more than it sounds
An overshoot is a contrast reversal
A curve tool has to decide what happens between the points you place, and the obvious choice is a cubic spline, which is smooth and easy to compute. It also overshoots: wherever your points turn sharply, the spline bulges past them before coming back. In a drawing that looks elegant, and in a tone curve it is a defect, because an overshoot that dips means a band of input tones comes out darker than the tones below it. That is a contrast reversal, and it shows up as a strange dark ring around a highlight or a flat patch in a gradient that nobody can explain. The interpolation here is monotone cubic with the Fritsch and Carlson slope limits, which constrains each tangent to at most three times the local secant. That condition is exactly what makes overshoot impossible rather than unlikely. We test it against the alternative. On a deliberately awkward set of points that rises the whole way, a plain Catmull-Rom spline through the same points overshot by 7 levels and produced 74 input values where the output went down, none of which the points asked for. The monotone curve produced 0 of each. Across 300 random rising point sets, Catmull-Rom introduced a reversal in 151 of them and the monotone curve in none. Worth being precise about the guarantee: it is that no reversal appears which your points did not ask for. If you deliberately drag a point below the one before it, the curve follows you down, as it should.
The curve goes through your points
The second thing to want from a curve tool is that it does what you told it. Some implementations smooth or approximate the control points, so the curve passes near them rather than through them and the value you carefully placed at 128 comes out at 131. Monotone cubic Hermite interpolation is exact at the knots by construction, so every point you place is honoured precisely. We verify it across a range of point sets: for every control point, the lookup table at that input equals the output you set, with a worst error of 0 levels. Below your first point and above your last, the curve holds flat at those values rather than extrapolating, which prevents a steep end section from running off and clipping tones you never touched.
What people use it for
Adding contrast properly
A gentle S is the most useful adjustment in photography, and curves is the only tool that gives you the shape directly.
Film emulation
Most film looks are a lifted black point plus a per-channel curve, which is two minutes of work here.
Colour grading
Lifting the foot of the blue curve puts blue in the shadows; lowering its top puts yellow in the highlights.
Rescuing flat photographs
A steeper midsection stretches the narrow range a flat photo occupies across the full scale.
Fixing a cast in one tonal range
When only the shadows are green, a single point on the green curve fixes it without touching anything else.
Product photography
Consistent curves across a set keep every product photo matching, which per-image auto adjustments never do.
Preparing for print
Print compresses shadows, so a small lift in the lower third often keeps more detail on paper.
Faded and matte looks
Raising the black point is the entire basis of the faded aesthetic, and it is one point.
Six tips worth knowing
Learn three shapes: the S for contrast, the inverted S for softening, and a lifted middle for brightness. They cover most of what you will ever need.
Use few points. Every extra point is another place the curve can do something you did not intend; three or four is enough for almost anything.
Keep sections gentle. A very steep part of the curve stretches a narrow range of tones across a wide one, which is how smooth skies turn into bands.
The RGB curve runs before the colour curves, so set your contrast first and grade afterwards.
Raising the bottom-left point is the whole faded film look. It is one drag.
Use a batch with fixed curves for a matching set, rather than adjusting each photo separately.
Troubleshooting
My gradients have bands in them
A section of your curve is too steep, stretching a few input values across many output values. Flatten that part of the curve.
The shadows went solid black
Your curve reaches zero before the input does. Drag the lower points up until detail returns.
Colours shifted when I only wanted contrast
Check you were on the RGB channel rather than one of the colour channels. A steep RGB curve can also increase saturation as a side effect.
A strange band appeared in a smooth area
That is what an overshooting spline causes, and it should not happen here. Check whether the source image already had banding, which a steep curve will amplify.
Frequently asked questions
What does a curves adjustment do?
It maps every input brightness to an output brightness along a shape you draw. That single idea covers brightness, contrast, black and white points and colour grading, which is why it is the most capable tonal tool there is.
How is it different from levels?
Levels gives you three fixed controls: black point, white point and midtone. Curves lets you place as many points as you like anywhere, so you can change one part of the tonal range without touching the rest.
What is an overshoot and why does it matter?
An ordinary spline bulges past your points wherever they turn sharply. In a tone curve a downward bulge means a band of tones comes out darker than the tones below it, which is a contrast reversal that shows as a strange ring or patch.
How does this avoid it?
Monotone cubic interpolation with the Fritsch and Carlson slope limits, which constrain each tangent to at most three times the local secant. Across 300 random rising point sets a Catmull-Rom spline introduced a reversal in 151 of them; this introduced none. If you deliberately place a point lower than the one before it the curve does follow you down, which is correct; what it never does is add a reversal you did not ask for.
Does the curve pass exactly through my points?
Yes. Monotone cubic Hermite interpolation is exact at the knots by construction. Across a range of point sets, the lookup table at each control input matched the value you set with a worst error of 0 levels.
What happens outside my first and last points?
The curve holds flat at those values rather than extrapolating, so a steep end section cannot run away and clip tones you never intended to touch.
What is an S-curve?
The upper part of the curve lifted and the lower part lowered. It brightens highlights and darkens shadows, which increases contrast, and it is the most useful single adjustment in photography.
How do I make a faded film look?
Drag the bottom-left point upward so black becomes dark grey. That is the entire basis of the look, and adding a small lift to the blue curve's foot makes the shadows cool as well.
Why do my gradients have bands now?
A section of your curve is too steep, stretching a few input values across many output values so the steps between them become visible. Flatten that section, or use the deband tool afterwards.
In what order are the curves applied?
The RGB curve runs first, and its result feeds the red, green and blue curves. That means a master contrast change carries through into whatever colour work you layer on top.
How many points should I use?
Three or four for almost anything. Every extra point is another place the curve can do something you did not intend, and complex curves are much harder to reason about than they look.
Can I use curves for colour correction?
Yes, and it is one of the best uses. Lifting the foot of the blue curve puts blue into the shadows; lowering its top puts yellow into the highlights. Between those two you have most of a film look.
Are my photos uploaded to a server?
No. The curve maths and the export both run in your browser using the canvas API. Nothing is sent anywhere.
Which format should I export?
Keep the original for photographs, at quality 90 or above. Steep curves stretch tonal differences and exaggerate any JPEG artefacts already present.
Is transparency preserved?
Yes for PNG and WebP output. The alpha channel is untouched. JPG has no alpha, so transparent areas are filled with the background colour first.
Can I apply the same curves to a batch?
Yes, and that is the main reason to use one. Fixed curves across a set keep every image matching, which per-image adjustments never do.
Can the adjustment be undone?
Gentle curves are very nearly reversible, but any section that flattens completely has merged tones that cannot be separated again. Keep your original either way.
Does it add a watermark or need an account?
No to both. No sign-up, no email wall, no daily limit and no watermark on the output.