"Custom" filter, I believe many people do not know what it is used, it is difficult to find relevant information, the following is the official Adobe Commentary: Custom (Photoshop) allows you to design your own filter effect.
Using the custom filter, you can change the brightness values for each pixel in the image, based on predefined mathematical operations called convolution. To reassign a value for each pixel based on the surrounding pixel value, this action
Similar to the addition and subtraction of channels, you can store custom filters that you create and use them with other Photoshop images.
For all the photos, the most important thing is how to make full use of light to take photos, if the use of light can not be reasonable, the contrast of the photos will be greatly reduced, if so, we can only in the latter aspect of the photo
The appropriate remedy was made.
Here are a few exercise footage to explain how to modify the photo with the custom filter.
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