Traditional Culture Encyclopedia - Photography and portraiture - What is the difference between mechanical retouching and artistic retouching in ps?

What is the difference between mechanical retouching and artistic retouching in ps?

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If the histogram is the photographer's "X-ray film", then the curve tool must be the photographer's "scalpel".

As an important tool for tone adjustment, curve not only exists in Photoshop, but also occupies a prominent position in many mobile phone softwares such as ACR and Lightroom.

In this paper, we will describe in detail what RGB curve is and how to adjust the tone of photos by using basic forms such as bright and dark, black and white field, contrast and local adjustment curve. At the same time, it will also explain how to combine various basic curve forms to achieve more complex tone effects such as film, bleaching and Japanese.

Where is the curve tool?

In Lightroom and Adobe Camera Raw tools, the curve panel is the second panel after the basic panel, which is enough to feel its importance.

In Photoshop, we usually use the curve adjustment layer to change the curve. In the lower right corner of the layer panel in PS, the fourth icon is the "New Adjustment Layer" option. Click on it and select Curve to create a new Curve Adjustment Layer.

Create a new adjustment layer instead of directly changing the curve on the original layer. The advantage of this is that we can easily undo/undo any adjustments we have made.

What is the curve?

This paper will focus on the RGB channel curve, which is formed by the superposition of three channels: red (R), green (G) and blue (B), and can be "approximately" understood as the brightness curve of the picture.

The core of RGB curve adjustment is actually the transformation of the brightness of the original image.

The horizontal axis of the curve is the brightness distribution of the original image. From left to right, it is 0-value pure black, the middle gray value 1-254, and the rightmost pure white brightest value of 255. A histogram is superimposed on the horizontal axis to show how many pixels exist in each brightness of the original image.

The vertical axis of the curve is the brightness of the target image (after adjustment), and the brightness value from bottom to top is still 0-255. The line inside is our "curve". We take any point on the curve, its "input value" is the value corresponding to its horizontal axis, that is, the brightness in the original picture, and its "output value" is the value on its vertical axis, that is, the adjusted brightness value.

If no adjustment is made, the curve of the image will be a diagonal line, that is, the brightness values of the horizontal axis (original image) and the vertical axis (target image) are equal. For example, if I take a point on the curve, its input and output value is 193.

If I move this point up, I can see that the output value of this point becomes 232, which means that those points with brightness of 193 on the histogram of the original image are highlighted as brighter 232. At the same time, we can find a characteristic of the curve. When we change a point, the next point will also change, and the farther away from the adjustment point, the smaller the change. This makes the picture of curve adjustment smooth and natural in most cases.

By adding control points (anchor points) to the curve, we can change the curve into various shapes to achieve the desired tone effect. Next, I will further explain the curve through some basic curve shapes.

First, brighten and darken the curve.

Brightening and darkening a picture is not the same as we think, and the brightness values of all points in the picture are the same. For example, the lower curve increases all the brightness of the image by 64. This leads to two bad results:

(1) The direct overexposure of the highlight area of the picture overflows.

(2) The brightness of the shadow and black area of the picture is greatly improved, which makes the black field of the picture insufficient and seriously ashed.

So we usually use the following curve to highlight the picture, put the anchor point near the midrange and lift it up. In this way, the brightness of the photo is mainly improved in the middle tone. The brightness of high-light area is improved less to prevent overexposure. The black area of the shadow is not improved much, and the contrast of the image is well maintained.

Similarly, we want to darken a picture, and we also use painting points to pull down the middle tone of the picture. Protect the shadow area from underexposure and keep the contrast of the highlight white area.

Second, the black and white field curve

We call the darkest point in the photo a black field and the brightest point a white field. The difference between black and white fields determines the contrast of photos. By moving the left and right ends of the curve horizontally and vertically, the black-and-white field difference of the photo can be increased and decreased.

For example, the picture below is a gray low contrast picture. The darkest part of the picture is only dark gray with a brightness of more than 50, and the brightest part is only light gray with a brightness of more than 200. The black and white area of the photo has no pixels at all.

So I moved the extreme right of the curve to the left. At this time, all the pixels with the original brightness value (input value) of 2 19 are brightened to pure white, and the output value is 255. There is finally a bright white part in the photo.

Similarly, I set an anchor point on the leftmost side of the curve and pull it horizontally to the right. At this time, all dark gray areas with original brightness value of 55 are output as pure black areas with brightness of 0. Dark black appeared in the photo again. Through these two steps, we have increased the gap between the black and white fields of the photos and greatly improved the contrast of the photos.

Pictures with large differences between black and white fields are generally rich in layers, bright and sharp. But the difference between black and white fields of photos is not as high as possible. A big misunderstanding is that the black field of the photo must be 0 and the white field must be 255. Actually, it is not. For example, in this photo, the black field of the photo is 0, and there are many dark areas in the photo, which is quite different and may not be the effect we want.

I set an anchor point on the far left side of the curve and pulled it up vertically. In this way, the brightness of the pure black part with an input value of 0 is increased to 38. There is no pure black in the photo, and the darkest part (that is, the black field) is also dark gray with a brightness of 38. This photo looks hazy and elegant, which is in line with the atmosphere we want.

Third, the contrast curve.

Contrast curves are actually S-shaped curves and anti-S-shaped curves that almost everyone knows in photography.

The enhanced contrast curve (S-shaped curve) is actually to establish an anchor point at the highlight and improve it, to establish an anchor point at the shadow and lower it, and to draw a curve similar to the English letter S.

If we carefully observe the S curve, we may be able to understand the principle behind it. As mentioned in the previous tutorial, a photo is divided into black, shadow, midtone (exposure), highlight and white according to the brightness from low to high. Among them, the transition and details in the middle tone area are the most delicate. You can see the middle part of the S-shaped curve, and the input and output values change little. Therefore, the S-curve has little influence in the middle tone area, which protects the most detailed part of the photo well.

The white and black areas are at the end, and the S-shaped curve has little change in these brightness areas, which effectively prevents overexposure and underexposure from overflowing. S-curve is mainly to improve the brightness of the highlight part of the original image, reduce the brightness of the shadow part, and make the tone of the photo harder. Therefore, under the premise of protecting the details of black and white and midtones, S-curve effectively improves the contrast of photos, which has almost become a necessary step for most photos.

Similarly, if we lower the highlight anchor point and raise the shadow anchor point, an anti-S shape will be formed. Is to lower the contrast curve.

Fourth, the local adjustment of the curve

The first three curve shapes all act on the whole. However, a core idea in the post-digital era is to locally adjust different areas of photos so that each area can show the best effect without affecting other areas. For example, in this picture, the grass between the snow-capped mountains and the lake is dark and needs to be brightened.

If I directly apply the brightening curve, the grass will brighten, but the snow-capped mountains (highlights) and the sky (midtones) will be overexposed at once.

So I need to create two anchor points to pull back the highlights and midtones. In this way, this curve only improves the brightness of the shadow part of the photo.

There is a very useful tool when adjusting the curve locally. It's a hand icon in a circle. Click on it and move the mouse into the image, and the mouse becomes a straw. At the same time, in the right curve panel, the position of the pipette corresponding to the curve will be displayed in real time.

Click on the straw, and the point where the straw is located will correspond to an anchor point, which will be recorded on the histogram for our adjustment. For example, in this picture, I want to reduce the brightness of the dark mountain while maintaining the brightness of the white fog. So after I select the "hand" icon, I first click the mountain in the red circle of 1, and the corresponding anchor point of 1 is established in the curve. Click the red circle 2 of the fog again, and the corresponding two anchor points will be established on the curve.

In this way, I pressed the 1 anchor point and kept two anchor points, only reducing the shadow mountain area, and the fog of highlights was not affected.

What is the RGB curve mentioned above? By highlighting the three basic forms of darkening curve, black-and-white field curve and contrast curve, and using them locally, the tone of a photo can be adjusted quickly. Next, I will talk about how to combine these basic curves to bring out complex timbre effects.

Similarly, although the three basic curves look simple, when we combine these basic forms, we can create various complex effects.

Five, dark tone effect curve

The picture below shows the white cliff in Seven Sisters, England. If we want to make it darker, it looks like the end of the world. How should I adjust?

Directly using the darkening curve we have learned, we can find that the middle tone of the photo has reached the low tone we want.

But in this case, the dark part is almost completely black and the details are lost. So I added an anchor point in the dark, which is equivalent to applying brightness curves in the dark and local areas.

Although the details of the dark parts have come back, the shadows are seriously grayed, and the dark clouds have completely lost their three-dimensional sense. Therefore, two anchor points are established in the dark part, and an S-shaped curve is superimposed to improve the contrast of the dark part. It can be found that the hierarchical contrast inside the dark clouds in the sky is displayed again.

Finally, an anchor point is also established in the highlight area, which is equivalent to superimposing a local brightness curve on the highlight part to restore the brightness of the highlight.

The final curve of this darkened photo = global darkening curve+darkening brightness curve+darkening contrast curve+brightening brightness curve. It seems complicated, in fact, as long as you understand that the principle is simple, the three basic curves are applied step by step.

Six, the film effect curve

The picture below is a photo of the Gome railway market in Thailand, if we want to make it more like a movie. How should I adjust?

The simplest method is to directly apply the color lookup table (3D-Lut) tool in PS or use various third-party film filters. A variety of preset film LUTs can quickly bring different types of film shadows and tones to the picture. But in fact, these effects can also be achieved through curves.

Careful observation of the shooting effect of Kodak 52 18 film LUT shows that its histogram has obvious right shift while maintaining the contrast, and there are no pixels in the black area at all. The gray dark part gives us the illusion that the details of the dark part of the photo are very rich, and it looks like it was shot with high weather-resistant film.

It is very simple to eliminate the black pixels in the histogram. We can use the black and white field curve we have learned to improve the black field anchor point (vertical) of the photo.

However, not only the dark part of the photo is gray, but also the midtones and highlights are gray. So in order to restore the contrast, I will draw an S-shaped curve (increase the contrast curve) on the basis of the above curve. In this way, this photo gets a lot of film-like tones, and the dark parts are gray but the contrast is enough.

After that, we can continue to apply color adjustment tools such as optional color, gradient mapping, hue saturation and so on to add film tones to photos, and these color adjustment tools will continue to be developed in future tutorials.

The film curve here = black field enhancement curve+contrast enhancement curve. We don't need to memorize this formula, because some movie special effects need to reduce the contrast. As long as you know the three basic curve shapes, you can combine various effects.

Seven, pressing black bleaching effect curve

The effect of blackening and bleaching is very suitable for people with strong sports, tough themes and strong feelings. Its characteristics are as shown in the figure below, with a large number of pure black or pure white areas, and the contrast is strong.

The following is the original film of this armored vehicle speeding on the highway. The contrast is not strong enough to reflect the impact of armored soldiers.

Use the black and white field curve to move the black field anchor point to the right, and all the dark parts in the photo will become pure black. Black is enough, but the side effect of black-and-white field curve is to darken the whole picture.

Therefore, anchor points are established in the bright parts, and highlights and midtones are improved by brightening curves to create a tough contrast effect. This effect of enlarging the pure black and brightening the bright part is called the broken black effect.

Similar to pressing black, it also has bleaching effect. As the name implies, the bleaching effect is that the whole photo becomes brighter, and the white overflows, while the dark part also becomes brighter and compressed into dark gray, just like the photo is printed on paper and then bleached in bleaching water.

The first two parts of the bleaching curve are the same as the blackening curve. Turn the dark part into pure black first, and brighten the photo at the same time. The bleaching effect will further make the highlights overflow into white. Although the details are lost, the photos will have a brighter and more dynamic atmosphere.

This effect can be achieved by moving the white area anchor point to the left in the curve. Finally, we move the point of the black field up a distance, which can be understood as the dark part that has just been compressed into pure black and lit up into the same kind of dark gray.

abstract

It can be seen that no matter the film curve, dark tone curve or blackening bleaching curve, no matter how complicated the effect is. Its essence is still the combination of three basic curves: light and dark, black and white field and contrast, in the whole, in every part!

So we don't need to remember what the curves of these complex effects look like. As long as you understand the functions of the three basic curve forms, you can combine all kinds of timbre effects you want according to your own needs!