[Cub] Add option to enhance background image

[mmaismma]

Description

Many hermits, not cubfan135 though, enhance their thumbnail's background image. Notable examples include rendog and Mumbo Jumbo.

These images are clearly brightened, saturated, and have increased contrast.

Possible solution(s)

CanvasRenderingContext2d has filter property which was made for like this purpose only. It is similar to the CSS filter property and accepts the same values.

Example:
There is a button. On clicking the button the image gets auto enhanced and a menu appears which can be used to customize the amount of saturation, brightness, contrast, etc.

[mmaismma]

After some experimenting, I found that this filter expression serves nice as the default parameter:

contrast(110%) brightness(110%) saturate(110%)

The order is important. In this order, contrast gets applied first and saturate at last.