Add interlaced option

[luckyraul]

@sindresorhus create new PR

[sindresorhus]

This needs to be documented. [,,] - #16 (comment)

[sindresorhus]

I think you need to work more on the docs. Interlaced and progressive are not the same thing.

[luckyraul]

@sindresorhus Copy paste from https://imageoptim.com/help/prefs.html#optipng

[sindresorhus]

@luckyraul That doesn't matter. We have high standards for the docs.

[kevva]

@sindresorhus, I believe interlaced is just a flag for generating progressive images. I just think "progressive" is the general description of it.

[sindresorhus]

Interlaced is the opposite of progressive.

[kevva]

Every article and documentation I read is referring to progressive rendering when mentioning interlacing. I don't know for sure though. You can read about it on OptiPNG own documentation as well http://optipng.sourceforge.net/pngtech/optipng.html.

[luckyraul]

Interlacing, useful for a faster, progressive rendering, is another component of the PNG image type that affects compression.
http://optipng.sourceforge.net/pngtech/optipng.html

[kevva]

From http://optipng.sourceforge.net/optipng-0.7.7.man.pdf:

If the interlace type 0 is selected, the output image shall be non-interlaced (i.e. progressive-scanned). If the interlace type 1 is selected, the output image shall be interlaced using the Adam7
method. By default, the output shall have the same interlace type as the input.

To me that sounds like "progressive rendering" and "progressive scanned" are two different things.

[kevva]

@luckyraul, can you fix the merge conflicts?

[kevva]

Thanks, I will merge this tomorrow.