Add PngWriteDefines

[dlemstra]

The PNG encoder has various options that are used when creating the output image. The following options should be added to the new PgnWriteDefines class:

• png:bit-depth (1,2,4,8,16 (maybe enum?))
• png:color-type (should use ColorType enum for the input)
• png:preserve-colormap
• png:preserve-iCCP
• png:exclude-chunks and png:exclude-chunks (flags enum (also add all and none))

[PikminGuts92]

Found this because I'm trying to save a black & white image as PNG with a bit depth of 8. Write method is defaulting to using bit depth of 1. Is there a workaround to use for now?

[dlemstra]

@PikminGuts92 I am not sure but I think you can do this: image.Settings.SetDefine(MagickFormat.Png, "bit-depth", "8").

[PikminGuts92]

@dlemstra Thank you. That seems to have done the trick.

[dlemstra]

The following options should also be included:

• png:compression-level
• png:compression-strategy (enum?)
• png:compression-filter