Port Dominant Color from performance plugin to core

[pbearne]

As part of the performance module life cycle, we want to port this site health check to the core.
​https://github.com/WordPress/performance/tree/trunk/modules/images/dominant-color

Performance issue GH link: ​https://github.com/WordPress/performance/issues/417

Trac ticket: https://core.trac.wordpress.org/ticket/56151

[joyously]

When I was writing a similar function, I noticed that using a 1 x 1 resize results in a muddy color that is sort of the average of the colors in the image, but not any of those colors.
The test cases use a lot of single color images to test with, so you might not see this.

@pbearne Coding standard issues.

[pbearne]

Replying to joyously:

When I was writing a similar function, I noticed that using a 1 x 1 resize results in a muddy color that is sort of the average of the colors in the image, but not any of those colors.
The test cases use a lot of single color images to test with, so you might not see this.

Yes, the colors are muddy/muted which is fine for this use

[johnbillion]

Proposal: ​https://make.wordpress.org/core/2022/07/21/proposal-add-a-dominant-color-background-to-images/

this version has a theme feature flag option

Trac ticket: https://core.trac.wordpress.org/ticket/56151

this version has a theme feature flag option

Trac ticket: https://core.trac.wordpress.org/ticket/56151

All references to dominant_color_ function names should be renamed to wp_dominant_color_

@pbearne Before assigning me to code review, please ensure that coding standards and unit tests are passing.

[davidbaumwald]

Thinking and talking about this during WCUS, I am on board with gathering the dominant color of the image on upload and saving it with the rest of the serialized metadata.

However, I still think the usage of the meta should purely be a theme decision. Duotone images were one instance I thought about where a user would potentially get a color not represented in the image.

[pbearne]

Replying to davidbaumwald:

Thinking and talking about this during WCUS, I am on board with gathering the dominant color of the image on upload and saving it with the rest of the serialized metadata.

However, I still think the usage of the meta should purely be a theme decision. Duotone images were one instance I thought about where a user would potentially get a color not represented in the image.

that is why we have added the theme support flag so fin grain control can be done via the theme :-)