Application of channel in image processing III
4. Mask and map mixing channel
mask is also called "Mask", which can be said to be the channel application that best reflects the meaning of "Mask"
add a black-and-white gray-scale image on an image (or a layer), and the image of the black part will be hidden (not deleted) and become transparent; The white part will be fully displayed; The gray-scale part will be translucent. Masks have irreplaceable functions in both image synthesis and special effects production. Masks can also be applied to the mapping of 3D models. Rust stains on metal, decal patterns on glass, and irregular shapes are often treated with rectangular maps and masks. Because this type of mask needs to adjust their coordinate position on the three-dimensional surface, it is often regarded as a special form of map, called "transparency map"
masks can be used not only in simple maps, but also in complex multi-dimensional materials. When two materials are mixed alternately on the same surface, people also need to use channels to deal with their distribution. Unlike ordinary masks, such a "mixing channel" is directly applied to two images: the black part shows the a image; The white part shows the B image; Gray scale part is both. It can be seen that the hybrid channel is a simplified application derived from the concept of mask, which is used to control the overlay relationship between two images
5. displacement mapping and bump mapping
in 3D software, channels are not limited to processing planar maps. They are also used to represent more complex materials, and even to build models
imagine that we need to model a coin: the complex patterns and patterns on its surface will definitely bring us a lot of trouble, which can hardly be completed with the usual modeling methods. Some people may ask: can we use a plane image to represent the ups and downs of the three-dimensional object surface (like an altitude map), and let the computer automatically complete the tedious modeling work? The answer is: Yes, and this key plan is the channel
paste a channel to the surface of the object in the way of so-called "displacement mapping". At this time, the computer will operate like this: the nodes on the mapped surface will be pulled and stretched along the normal direction of the surface at the point according to the brightness information of the pixels on the mapped channel, or concave, Or protrude: it's like looking at a transmission "Wiggs painted a map of altitude in order to open up a strong market for polyketones, pinching mountains and valleys out of the mud. Now, as long as we use a flat drawing tool to draw a two-dimensional image, and then convert it into a displacement map and give it to the object, a coin with great texture will pop up on the paper.
displacement map can greatly save modeling workload, but because the generated model is not optimized enough, Too many polygons will cause a sharp increase in rendering time. To this end, people come up with a good compromise. Without increasing the complexity of the model, the bump effect of the object surface is similar to the real model generated in the displacement map, which is the bump mapping algorithm. The bump map also takes the channel as the information source. By pressing the "start" key on the counter, the surface map and shadow processing can show the highlight and shadow of the object, so that its shadow effect can reach a convincing level in most cases
now, we use bump channel mapping to build a coin model, and compare it with the previous displacement model. We will find that the latter has the same excellent performance as the former when "facing" the processed plane (the line of sight is perpendicular to the plane), but the rendering time is much better than the former; When compared with the "side view" (the line of sight is perpendicular to the normal of the plane), the displacement map still shows the real undulating shape of the object surface, while the plane treated with bump map is flat as before. This also exposes the shortcomings of bump mapping. The above two algorithms have their own advantages and disadvantages, and the perspective becomes the decisive factor when finally deciding which algorithm to use to combine the channel with the model to achieve the desired effect
6. vector channel
in order to reduce the amount of data, people analyze the digital image depicted point by point again, and use complex calculation methods to convert the point, line, surface and color information on it into simple mathematical formulas; This kind of formulaic graphics is called "vector graphics"; The formulated channel is called "vector channel". Although vector graphics can compress image information hundreds of times, which Rockwell hardness tester should be selected? The following is the detailed analysis quantity given by hengsi Shanda company, but its calculation method is too complex, and the transformation effect is often unsatisfactory. Therefore, he can only be useful in the performance of geometric figures with simple outline and bright color blocks; When dealing with real effects (such as photos), it is rarely used. The "path" in Photoshop, several preset maps in 3ds, and the mask in vector drawing software such as illustrator and flash all belong to this type of channel
the ancients said, "don't build a high platform in the sand". If you want to have excellent technology, you must strive to learn basic knowledge well. The application of channel is the only way for people engaged in art industry from entry to proficiency, and it is also the colorful movement of this course. I hope you can learn bit by bit from here, and let your works shine artistically in the near future. (text/ChenYuXin)
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