Panoramic mosaic and post-synthesis skills

Author? Yu Yuwen? (Published in the second issue of Popular Photography 202 1)

What is the difficulty of panoramic stitching?

Panoramic tags are divided into horizontal tags, vertical tags and matrix tags. The first two kinds of stitching are relatively simple, and the desired scene can be shot by pressing stubble horizontally and vertically. The latter is a bit difficult, and it is necessary to carefully observe the shooting scene, whether it is horizontal or vertical, and shoot more and more rows. It must be calculated accurately, and it needs to be shot many times and compared repeatedly, until it is fully mastered, before the official shooting can begin. It's easy to say the scene around you. It's hard to go to a place where it's hard to go again to shoot Zhang Quanjing. In other words, if you don't pay attention to the details in the early stage of shooting, it will be very difficult to operate in the later stage, and you will fall into the embarrassing situation that the computer can't take the film automatically and the manual taking is inaccurate.

It's not difficult to make a movie. It's crucial to master the tricks. Focus on the following "four words" essentials.

? (1) flat. The first is to try to choose a flat plane. It is relatively easy on roads and roofs, but it is more difficult on hillsides and valleys. The second is to level the tripod head as much as possible. The third is to level the camera. Slightly high-end cameras have a level, so whether shooting horizontally or vertically, the level should be adjusted to a green horizontal line, and the vertical level is not necessarily horizontal because of the pitch angle. Generally speaking, the connectors are shot vertically, so it is particularly important to check whether the camera can keep horizontal when rotating. It is not allowed to level the camera only for the middle main scene without paying attention to both ends.

? (2) stability. The main thing is to keep the tripod steady, and try to choose a strong tripod to ensure that it does not shake when shooting in rotation or when it is windy. In the process of rotating shooting, it should be smooth, not high and low, fast and slow, and it is best to use automatic panoramic pan/tilt. The anti-shake function of the camera and lens is turned off. Generally speaking, cable release is used to control the camera. If there is no cable release, the camera comes with a 2-second selfie.

? (3) quasi. The first is photometric accuracy. When shooting, the brightness of the picture is often different, so you should choose a place with moderate light and shade for metering. After photometry is confirmed, lock the exposure lock to ensure the exposure value of the entire tab is consistent. If you take a photo and measure the light once, it will be uneven and difficult to adjust. If shooting in a scene with large light ratio, it is best to use a single HDR patch.

The second is accurate focusing. Generally, a fixed-focus lens is used to shoot panoramic images. Try not to choose a super wide-angle lens because the distortion is too large. It is not impossible to use a zoom lens, but the focal length of each patch must be the same. Panoramic stitching usually adopts manual focusing mode, because the focus of distant view and close view is different, and each photo needs fine focusing.

The third is accurate stubble pressing. When shooting with a rotating camera, if you only shoot a row of bars from left to right, let the two pictures be at least one-third stubble; If you only shoot a row of longitudinal seams from top to bottom, there must be at least half of the stubble in the two pictures; If the shooting matrix is spliced, press one-third crop from left to right and one-half crop from top to bottom. In short, the more stubble is pressed, the smaller the distortion is. Sometimes I even push it up and down to 80%. It is particularly important to note that when stitching the shooting matrix, no matter how many rows are shot up and down, the number of sheets in each row must be the same, and the position of the stubble in the upper and lower rows should be on a vertical line as far as possible, so that no accidents will occur during stitching. Leave some margin when shooting, because some pictures will be lost in later cropping.

? (4) fast. Generally speaking, filming is a big scene. On the basis of stability, it is necessary to achieve the consistency of light and shadow, the consistency of light and shade, and the reasonable connection, so as not to reproduce moving objects. One is to shoot the sunrise and sunset quickly. It takes only a few seconds for the sunrise and sunset to shine on the building. Slowness not only misses the best shooting opportunity, but also causes the light and shadow of the whole picture to be inconsistent. The second is to quickly shoot the night view of the city. Night scenes are usually taken when the sun is just setting and the lights are just on, which is not only short-lived, but also the main building and the sky will be different with the delay of time. The third is to be fast when there are moving objects in the scene. Taking pictures often likes to capture interesting elements such as birds, planes, trains, cars, boats and yachts, especially colorful clouds, rainbows, flying clouds and the light of Jesus. Some are fleeting, and some are ever-changing. If they procrastinate, they can't catch the wonderful moment, or there will be double images, or stubble will break.

There are three most commonly used and basic composition methods for panoramic mosaic: one is three-point composition. This composition method divides the picture into nine equal squares with four straight lines, and puts the interesting center at the intersection of the straight lines. The second is symmetrical composition. This composition has the characteristics of balance, stability and echo, but the disadvantage is that it is too rigid and lacks change. It is often used to express symmetrical objects, buildings, reflections and other special style objects. The third is the framework. This kind of framing prospect can attract the audience's attention to the scenery in the picture, highlight the main body and produce a sense of depth.

Figure 1: First, create a new folder, and put multiple material pictures to be spliced into this folder. Open Adobe Bridge CC 2020, click "Folder" to open the material picture, select all, and click "Open in Camera Raw" on the page.

Figure 2: In the mosaic interface, select all the pictures, and then select "Merge to Panorama" to start panoramic mosaic.

Figure 3: Enter the tab interface. Under the Projection dialog box on the right side of the layout, select one of the effects of Sphere, Cylinder and Perspective as required. "Boundary Distortion" is adjusted according to the image situation. Don't choose the distorted "Fill Edge" matrix stitching, and don't choose "Apply Auto Settings" and "Auto Crop". Click "Merge" after splicing.

Figure 4: After automatic splicing, deformation correction is generally needed, and the graphics can be adjusted by "Edit/Transform/Perspective, Distortion and Deformation" in Photoshop CC 202 1. After cutting, adjust according to the methods and steps of adjusting the scenery film until you are satisfied.