Film Material Picking-How to Pick with the Magic Hand of Light and Shadow

AE Keying Technology in Film and Television Post-production

AE keying technology has been widely used in many fields related to film and television processing, and has become an indispensable link in later film and television processing. This paper introduces AE keying technology in film and television post-production in detail from the definition, material preparation and basic technology of post-keying, and finally further analyzes the application of AE keying technology through practical cases.

1, key definition

Keying refers to extracting a specified image from a picture or video picture in post-processing and synthesizing the extracted image into a new scene, thus increasing the vividness of the picture, which is called keying in technical terms. Generally speaking, keying refers to taking a certain color value or brightness value in an image to define a transparent area. All pixels with similar colors or brightness values in the picture become transparent, so as to extract the subject. Nowadays, key imaging technology has become an indispensable link in most post-film and television processing.

2. Material preparation

For the video material to be keyed, the early shooting and preparation work is very important, which almost determines the final effect of keying. According to the principle of keying technology: a certain color in the video picture is converted into transparency and the Alpha channel is extracted, so keying technology usually requires the background color of the lens picture to be as single as possible. Therefore, in the actual shooting process, the subject is usually required to complete the action performance of the film in front of a relatively single and high-purity color background. Theoretically, the background color can be any color that does not exist in the foreground color. We usually use blue or green background in real shots, because people's bodies do not contain these two colors. China people's skin color is mostly yellow, generally with yellow complementary color DD blue background. After the sample is sent to keying, the skin color will be whiter, which can achieve better results. However, the color effect of yellow skin in front of green background is slightly worse than that of blue background. In western countries, because many Europeans and Americans have eyes close to blue, they often use green backgrounds when shooting people. Usually, the shots to be keyed will be shot in a professional solid color studio. At present, the most widely used is the "blue box" shooting. In this way, the blue background can be removed in post-production and then the foreground can be synthesized with other materials. Blue box technology is widely used at present, such as the movie Avatar. The shot material is collected in the computer and processed by post-production software.

3. The basic technology of late keying.

In the post-production of keying, the collected materials are mainly keyed by film and television post-production software, keying special effects or plug-ins, so as to preserve the foreground and remove unnecessary background. Through key treatment, its new background material is synthetic. In the later period of keying, the commonly used keying techniques are: chroma key (blue screen or green screen keying), brightness key, difference key and so on.

3. 1 chroma key

Chromaticity key, also known as color key, is a technology that software automatically removes a color and its similar colors from an image by specifying a color. Blue screen keying and green screen keying are commonly used, but in principle, the background is not necessarily blue or green, and other solid colors can be selected. Generally speaking, the greater the contrast between the color to be keyed and the color to be retained, the better the color keying. In the later effect, the adjustment of special effects is a very delicate process. A good keying effect can not only keep the foreground pixels completely, but also remove the background pixels cleanly. At the same time, if the foreground contains semi-transparent pixels and soft areas, this information should also be kept intact in order to prepare for the subsequent post-synthesis. The method and main parameters are adjusted as follows:

(1) Select a picture or video to adjust and use the command effects/keying/colorkey. Use the eyedropper tool to absorb the color that needs to be deducted (that is, the color that needs to become transparent).

(2) Adjust the value of colortolerance, that is, control the color tolerance. The higher the value, the more transparent the specified color is.

(3) Adjust the value of edgefeather. edge feather is the feathering effect of the control area, which can be adjusted slightly, but not too big.

3.2 brightness key

The technology of keying by brightness difference is called brightness keying. That is, select parts with similar brightness to make them transparent. When the subject is very bright, put it in front of a dark background to shoot, and the light will only illuminate the subject, so that a photo with a completely black background and a bright foreground will be taken. Then the channel is extracted according to the brightness difference by brightness keying technology. This matting method is usually used to shoot scenes with large contrast between foreground and background light, such as cutting black characters from white paper. The method and main parameters are adjusted as follows:

(1) Select a picture or video to adjust. Select the keying type first by using the command effects/keying/lumakey. By specifying a value for the key type, for example, selecting keyoutbringter view mode, pixels with brightness values higher than the specified value will become transparent.

(2) Adjust the tolerance value, which is used to set the range of the specified brightness value. The lower the value, the closer the extracted brightness value is to the specified brightness value.

(3) Adjust the value of Edgefeather, which is used to set the extracted edge feathering degree. The larger the value, the softer the edges. However, if the value is large, it will also lead to a long rendering time.

(4) Adjust the value of Edgethin, and set the thickness of the edge of the extraction area through positive and negative values. A positive value will increase the transparent area, while a negative value will decrease the transparent area.

3.3 Difference key

The transparent area defined based on the basic background image is called the difference key. Through the differential key, not only the solid background can be dug out, but also any background can be dug out. It uses two different colors to key the image. In actual shooting, when there is no condition for blue screen or green screen shooting, or the shooting action can not achieve the effect of solid color keying, you can use the difference key to key. Differential keys also have some disadvantages. Due to the subtle changes of shooting light, video noise, film particles and other possible factors, the background before and after shooting is not the same, so it is difficult to extract pure channels. In practical application, differential key is also a very practical key technology. The method and main parameters are adjusted as follows:

(1) Select the picture or video to be adjusted and use the command effects/keying/colorificationkey. In fact, when we use this command, we can see from the picture that the background is basically transparent, but the local effect may not be very good and needs further adjustment.

(2) In view mode, select mask mode, view/mattecorrected. Among the three eyedropper tools, the second eyedropper is used to specify the transparent area and the third eyedropper is used to specify the opaque area. Then we can get better results by fine-tuning the parameters related to partialAin**/partialAout**.

3.4 Key Keying

Keylight plug-in is a very effective, convenient and powerful keystroke tool, which has been acquired by Adobe and turned into an internal plug-in. Plug-ins can identify pictures by selecting key colors and remove the selected colors. By adjusting the three colors of black, white and gray in the screen mask mode. Black means completely transparent, white means completely opaque, and gray means translucent. By adjusting the alpha channel, we can select the satisfactory effect. The method and main parameters are adjusted as follows:

(1) Select a picture or video to adjust, and use the command Effect/Keying/Keylight to add a Keylight effect. In the Screencolour option, use the eyedropper tool to absorb the color that needs to be deducted (that is, the color that needs to become transparent).

(2) Adjust the value of the Screenpre-blur parameter, not too much. If it is too large, the details of the image edge will be lost. The numerical value should be adjusted to the best effect according to the actual situation, that is, the edge of the image is softer.

(3) Switch to the Screenmatte option to further adjust the tuning range. The white area represents the reserved part, and the black area represents the cut part. By adjusting the values of two parameters, clipblack and clipwhite, the gray part in the material can be turned into black or white. If there is less gray, you can adjust the screengain directly to adjust the color.

(4) Adjust the values of Alphabias and Despillbias parameters, and carry out anti-overflow adjustment on the image edge.

4. Take the basic key technology colorkey as an example.

The following uses colorkey keying technology to complete a "background replacement of cartoon pictures".

1) Start AE software, import two materials as shown in the figure below, and create a new composition in the project window, named "cartoon picture background replacement". Select two material pictures in the project window, add the pictures to the newly created synthetic "cartoon picture background replacement", and rename the two layers as "cartoon picture" and "background" respectively.

2) Select "cartoon picture", select the command effects/keying/colorkey, select the eyedropper tool in the keycolor column, and click on the blue part of the composition window to absorb the color removed by the key, as shown in figure 1.

5. Concluding remarks

In the later effect, there are many kinds of keying techniques, and each keying method should have its own characteristics and advantages. In practical application, the most suitable keying method should be selected according to the actual situation of materials. Sometimes, for complex keying processing, it may be necessary to combine two or more methods to obtain satisfactory results. Finally, it is necessary to adjust the color saturation of the keyed picture and the background scene to ensure that the final fused picture can have similar color environment. Using AE keying technology can finally provide us with clearer, more vivid and realistic visual effects.

What are the methods and skills in the later work of video editing? First, film and television editing practitioners must:

1. Look for * * *' s expression and action in limited materials.

2. The ability to cut materials and find their connection with the next picture.

3. Ability to use images and choose music, and creativity to create melodies and plots.

4. The editor should also give the film a sense of jumping composed of continuous still pictures and inject life into the image.

5. The editor will naturally find the best expression in many shots and find out which point is the tangent point, which is the melody sense of the clip. At the same time, the whole picture of the work will be slowly presented in many photographic materials. Through the material, you can see what the work should look like.

Second, the method of finding the shear point:

Where should I cut and connect? Finding the breakthrough point is undoubtedly one of the important tasks of editors. One thing to note here is that this is the vertex of the picture.

Lianyi believes that the so-called picture vertex refers to the turning point of action and expression, such as the moment when the character's arm is fully extended, the moment when he nods his head, the moment when the sphere rises and is about to fall, and the moment when the smile is withdrawn.

The image is a series of still pictures, because the previous film will form afterimages in the human eye, so the pictures on the film look dynamic.

Therefore, the more intense the action is, cutting at the top of the picture or at the moment before the action begins will have a strong afterimage effect on the film behind, leaving a deep impression on the audience.

Three: the tangent point that produces a sense of melody.

Let's take the action of turning pages as an example to see how to find the starting point.

If you start shooting from the state where the action stops completely, faithfully shoot the action of turning the book from beginning to end, so that the audience can know that it is the action of turning the book at a glance.

However, the beauty of the image cannot be reflected only by clarity, and the sense of melody and comfort are equally indispensable. So what should we do?

We choose the initial cutting point in the state that the book turning action has started. If the page turning action is decomposed into 1 ~ 24 pictures, then the first 3 ~ 4 clips are cut out as the initial cutting points.

This change has no effect on understanding the action of turning pages. On the contrary, it can also show the melody and comfort of the action. This editing method can also be applied to other images.

Four: There is not only one correct method for film editing.

How to use the magic hand of light and shadow to cut the picture? Potoshop's method of removing redundant objects and people is complicated, and it needs to be applied to stamp imitation tools, repair tools, stain repair tools, content identification and filling according to specific conditions.

For example, an example of removing redundant characters from a picture.

1. First, open a photo of a character in Potoshop.

2. Then, press "Ctrl+J" to copy the layer 1 to a new layer, which will become a copy of the layer 1

3. Select "Lasso Tool" to select the general outline of the character, as shown in the figure. Press "Shift+F5" to identify and fill in the content.

4. Repeat the above steps until the effect shown in the figure is achieved.

5. Finally, select the "Stamp Imitation Tool", press and hold the Alt key to absorb the original part as the source, and then smear the filling part.

6. Trim the imperfections slightly, and the final effect will be compared as shown in the figure below: