How can we make the sky bluer?

After a period of rainy weather, it is rare to see the blue sky for a few days. I believe everyone's interest in going out to shoot has also increased. However, have you found that even if you shoot under the blue sky, the depth of the blue sky will be a little different. What is it? Seasonal factors Even if you shoot in the same place and in the same direction, the blue sky photographed in summer and winter is different. In winter, the blue sky is light blue. In summer, the blue sky will be dark blue. Generally speaking, it is easier to shoot a dark blue sky from June to August every year. Shoot in winter on the left and shoot in the direction of the sun on the right in summer. Even on a sunny day, there is more or less a haze in the air. Xia Qi's influence on the blue sky is most obvious near the position of the sun, which often turns white. Only where the air is very clean will the sky near the sun appear blue. Therefore, even if there is a blue sky, the blue of the sky is not uniform. Blue is brightest near the sun, and the sky is darkest at a 90-degree angle with the direction of the sun. All you have to do is make a pistol-shaped gesture and point your index finger in the direction of the sun. The direction in which your thumb can turn is the darkest blue place in the sky. The closer the sky is to the sun, the lighter the blue will appear, and the direction in which the thumb can turn is the bluest part of the sky. There are two kinds of filters that can enhance the blue of the sky, namely polarizer and gradient filter. The most common use of polarizer is to strengthen the saturation of blue sky and make white clouds more obvious. When shooting, just slowly rotate the polarizer in front of the camera and carefully observe the color change of the sky from the viewfinder or LCD. When the sky turns to the deepest blue, it means that the polarizer has been adjusted to the best angle and can be photographed. But pay attention to the rotation of the front lens group when zooming or focusing, which will change the angle of the polarizer. On the left is a common CPL polarizer, and on the right is an ultra-thin polarizer. The latter is more suitable for ultra-wide-angle lenses, reducing the chance of black corners in photos. There is no polarizer effect on the left, and there are two gradient filters on the right: gradient gray or gradient blue. Adding gradient gray filter when shooting in sunny days can make the sky underexposed, improve color saturation, make the sky appear bluer and look more relaxed and happy. Gradient blue is another commonly used filter. On cloudy days, when the sky is not good, the gray sky is really a big scene. At this time, adding a gradient blue filter can restore the sky to blue and enhance the effect of blue sky and white clouds without affecting the color of the ground. On the left is the effect without filter, on the right is the effect with gradient gray filter, on the left is the effect without filter, and on the right is the effect with gradient blue filter. The post-processing of various gradient filters can easily deepen the blue of the sky with Photoshop and other software. Although it's a bit off topic, it's a useful method and I have to mention it here. After opening the file, select Image-> from the menu; Adjust (adjust-> Replace the color, point the eyedropper at the blue position in the sky, and the preview will show the selected position (white position). You can adjust the ambiguity to adjust the selected range. Then as long as the saturation in the replacement column is increased and the lightness is decreased, the blue color of the sky can be enhanced. But the adjustment range should not be too big, otherwise it will affect the blue gradient of the sky. Select image-> Adjustment-> "Replace Color" sets various parameters to complete the effect.