Curves guide: how to edit a photo with Photoshop’s most powerful tool | Articles | Photo, video, optics

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.

Pho­to: Eliz­a­beth Chechevic / instagram.com/chechevic_a

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.

In this case, it makes no sense to work on the right side of the curve, since there are no such bright pix­els in the pho­to. The main effect should be on the left side of the curve, where the shad­ows are / Illus­tra­tion by the author

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

Author’s illus­tra­tion

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.

Impor­tant clar­i­fi­ca­tion:

- 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.

Per-chan­nel increase in con­trast with simul­ta­ne­ous increase in bright­ness on the RGB curve. The con­trast is lift­ed by clas­sic s‑shaped curves. The steep­er they are, the stronger the con­trast will rise / Illus­tra­tion by the author

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

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.

On the left are approx­i­mate curve set­tings for a sepia effect. The top half of the pho­to is this effect with­out dis­col­oration, the bot­tom half is with the image pre-con­vert­ed to bw / Illus­tra­tion by the author

- 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.

Approx­i­mate curve set­tings for “choco­late” ton­ing. In this sit­u­a­tion, I had to addi­tion­al­ly use the blue curve to remove the extra “cold” from the pic­ture / Illus­tra­tion by the author

• 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:

• Brightness/Contrast
• Lev­els
• expo­si­tion
• Col­or bal­ance
• pho­to fil­ter

Mov­ing on to the slid­ers in ACR (Adobe Cam­era RAW) and Light­room. Work­ing with a curve can replace you:

• Tem­per­a­ture
• Tone
• expo­si­tion
• Con­trast
• Sve­ta
• Shad­ows
• Light
• Dark
• split ton­ing