Curves can be found everywhere. Photoshop, Lightroom, any more or less functional photo editing applications on your phone contain this tool. An unusual and not intuitive tool can drive a beginner into a stupor. But, once you figure it out, you get a versatile and incredibly powerful tool for a variety of work with color and tone, which behaves the same in any editor.
We explain what curves are, how to control them, and what quick effects they allow you to process a photo.
What are curves
Curves is a tool that can change the brightness of any pixel from black to white and change its color.
To understand which pixels can be changed and how, there is always a histogram against the background of the curve and the grid (each image has its own!). It shows how the brightness is distributed in the picture in the range from black to white.
Simply put, by looking at the histogram of a photo, you can find out:
- a dark picture or a light one (where the main array of pixels is concentrated — in shadows, highlights, midtones);
- how varied are the shades in the photograph (the width of the peaks in the histogram);
- whether the details in the shadows and highlights have disappeared, that is, whether the photo or its part is too dark or overexposed (if it is lost in the shadows, the histogram is close to the left edge of the window, if in the highlights — to the right);
- whether the contrast is “squeezed” out of the photo to the maximum, whether the tone in the picture is varied (if not, the edges of the histogram will be far from its borders).
It would seem, what does the curve have to do with it? Why are we talking about the histogram? Communication is simple. The histogram shows where which pixels are. Knowing this, we can use the curve to affect only certain areas without affecting the rest.
Another example: you photographed a portrait of a fair-skinned blonde against a black background. Understanding the histogram, you will find on the curve the area where the pixels that “shape” her face are located, and you can correct it — for example, increase the contrast or tone the skin.
What’s in the Curves panel
1. A histogram that shows how pixels are distributed on a luminance line.
2. Curve. Initially, it looks like a straight line cutting a square with a diagonal.
3. Points on a curve. They work with the curve. Points can be placed, raised and lowered. To delete a point, you can select it and press Delete, or “grab” it and drag it out of the tool.
4. Black point and white point. By moving them to the center horizontally, we can assign the lightest and darkest points in the picture, thereby making the picture full contrast. Raising the black point up, vertically, and the white point down, we lower the contrast.
All the pixels that are behind these points will turn into a continuous “mess” — the details will completely disappear there. If this is not a conscious creative decision, it is better not to allow this.
5. Scales of brightness below and to the left of the working area of the curve. They visualize where the bright pixels are, where they are dark, what brightness they are. For example, with the help of them you can track what the pixels of the black and white points will become if you lower or raise them.
6. Presets. A list with pre-installed curve parameters sewn in by developers. As a rule, they fall on the photo ugly, as these are pre-prepared average parameters. There is no preset that, without refinement, will suit any picture equally well.
7. Channel selection. RGB is the so-called master curve, which changes the brightness simultaneously in three channels. The remaining three curves correspond to the red, green and blue channels. Channel-by-channel work (with each curve separately) allows you to work with color, more accurately raise the contrast.
8. Hand. By turning on the tool, you can move it to any area in the photo, and it will show where on the curve the point is responsible for the pixels of this brightness.
9. Pipettes. Helps to put the point of black, white and gray. This is necessary to straighten the BB, bring the picture to full contrast.
10. “Round Curve Values”. Smoothes a curve drawn with a pencil. Each press of this button gradually straightens the curve you have obtained and therefore reduces the effect of its impact.
11. Pencil. Allows you to draw any curve. It is rarely used, as it strongly “breaks” the picture, gives unnatural colors and brightness.
12. Entry and exit. Shows where the point originally was and where it moved to, ranging from 0 (pure black) to 255 (pure white).
How can I process a photo with a curve
- Lighten or darken a photo
The main rule of the curve is that if you put a dot on it and raise it up, then the picture brightens, and if you lower it down, it darkens. All it takes is one click of the mouse.
- Raise Contrast
If we talk about brightness, then contrast is lightening the light and darkening the dark. When this difference intensifies, the photo seems more voluminous, contrasting.
The main thing to do when you turn up the contrast with a curve is to find where the object is to be affected. For example, a person’s face in a portrait or a building in an architectural photograph. This is necessary so that the correction is more accurate, local.
It turns out that to increase the contrast, you will need two points — the one that will be responsible for the darkest areas of the main object in the frame (it will need to be lowered down so that it becomes even darker), and the one that will be responsible for the light areas (it needs to be raised up so that the light becomes even lighter).
You can find these areas on the curve using the Hand tool. You need to point it on the photo first to the light area — a hollow circle will appear on the curve. Fix it by clicking the left mouse button and turning it into a point, and then lift this point up. We do the same with dark pixels, but we omit the point on the curve.
- if the photo is black and white, or there are few colors on it, an RGB curve will do;
- if you are working with a bright image with many shades, then you need to increase the contrast channel by channel, in each of the curves separately — Red, Green, Blue, and the master curve can be left for general brightness correction. In this case, you will have to tinker so that the color does not “give”, but the correction will be more effective and accurate.
Adjust the strength of the contrast by changing the height of the dots, or by changing the opacity of the layer.
Curve has great potential for photo toning and color fine-tuning. You can create a sunny, warm frame with reds and yellows, or make it cold and gloomy with blues and blues. For tinting, you will need per-channel Red, Green and Blue curves, which are responsible for changing the color. All we need to do is select a curve, put a point on it and move it, watching how the mood of the frame changes.
Each of the curves can bring its own color to the photo (red — red, green — green, blue — blue), but we can also remove it, add the opposite to it on the image. The red curve adds cyan, the green curve adds magenta, and the blue curve adds yellow.
Now let’s look at the effects that can be achieved by toning a photo using curves.
Special cases of toning:
- split toning
This is the addition of colors, and often opposite to each other, in the dark and light parts of the image. For example, shadows can be made cold by tinting them blue, and highlights can be made warm by adding yellow and other warm shades.
To create this effect, it is enough to shift the points of the black and white color curves, achieving the desired color combination. To, for example, make the shadows colder, the black point on the blue curve must be raised vertically upwards. And if you need to add yellow to them, then the black point in the blue crookedly needs to be shifted horizontally to the center.
Sepia is a light brown dye used to tint photographs during the film era. It turns out that you need to add warm shades to the picture — yellow, red and a pinch of purple. To enhance the effect of antiquity, desaturate the photo first. For example, using a Black and White adjustment layer.
- skin toning
You can refine the skin tone, make it warmer or colder, by working with the blue curve. The main thing is to erase the excess on the white mask, which is automatically added to each curve, with an ordinary black brush, if you do not want the effect to be applied to the entire image at once.
- retro toning effect
1. Slightly raise the contrast on the RGB curve.
2. Add heat by raising the red curve.
3. In the green channel, create a smooth S‑curve to add subtle purples and greens.
4. Repeat the previous point with the blue curve, but only the S‑shaped curve will be inverted — we add blue in the shadows, and yellow in the highlights.
- “chocolate” toning
Trendy toning on Instagram, which can be done in a curve in a couple of seconds without downloading presets and applications.
- Raise the black point in the red curve.
- Raise the black point in the master curve, and also dot the shadows and darken them.
- White Balance Correction
In order to correct the white balance, to make the colors natural, we need to add a color opposite to the parasitic color in the photo. For example, if you were photographing at home under warm lights, open the blue curve and add blue to the photo and cyan to the red curve. If you shot on a sunny day in the shade of greenery, it is likely that the face will have a greenish tint. You can remove it by adding magenta to the green curve.
Results. What tools can replace curves
All of the Photoshop, ACR, and Lightroom tools listed are variations on the Curve theme with limited functionality.
Now in Photoshop you can use only one curves instead of the following tools:
- Color balance
- photo filter
Moving on to the sliders in ACR (Adobe Camera RAW) and Lightroom. Working with a curve can replace you:
- split toning