The cargo install documentation is missing the following packages for debian/ubuntu systems:

• build-essential
• libxcursor-dev
• libxi-dev

I needed to install the latter two to compile the x11 dependencies in addition to the others in the docs, and I'm guessing you need the first.

I can’t change the opacity of a color, change brush or eraser size, rename, resize, or change color values via text.

![356dac6a-7873-4841-9717-6a8174269997](https://user-images.githubusercontent.com/13999159/38310028-87fcc1b8-37e9-11e8-8f2b-36198a26975a.pn

Is your feature request related to a problem? Please describe.
All the data need to be logged. That's why I think that the logging must be added to the image-comparison.

Describe the solution you'd like
The solution is to add SLF4J based on Log4j 2.* version.

Describe alternatives you've considered
Instead of the Log4J can be used Logback or even JUL(java.util.logging).
Th

@ekmett mentioned on reddit that he'd like some color distance computation added to Color:

One thing I'd really like to have would be DIN99o color distance computations

It seems like a pretty good idea, I wanna record it before I forget about it. There are sample