How to convert an image to ASTC format? (ASTC or KTX file)

With TexturePacker's --convert-texture command line option you can easily convert a single image to a different format:

TexturePacker --convert-texture input.png --pixel-format ASTC_6x6 --texture-format ktx

The pixel format specifies the compression algorithm to use, the texture format describes the file container. The following formats are supported for ASTC compression:

Pixel format	Bits per pixel	Description
`ASTC_4x4`	8.00	Compressed with ASTC 4x4
`ASTC_5x4`	6.40	Compressed with ASTC 5x4
`ASTC_5x5`	5.12	Compressed with ASTC 5x5
`ASTC_6x5`	4.27	Compressed with ASTC 6x5
`ASTC_6x6`	3.56	Compressed with ASTC 6x6
`ASTC_8x5`	3.20	Compressed with ASTC 8x5
`ASTC_8x6`	2.67	Compressed with ASTC 8x6
`ASTC_8x8`	2.00	Compressed with ASTC 8x8
`ASTC_10x5`	2.56	Compressed with ASTC 10x5
`ASTC_10x6`	2.13	Compressed with ASTC 10x6
`ASTC_10x8`	1.60	Compressed with ASTC 10x8
`ASTC_10x10`	1.28	Compressed with ASTC 10x10
`ASTC_12x10`	1.07	Compressed with ASTC 12x10
`ASTC_12x12`	0.89	Compressed with ASTC 12x12

Texture Format	Description
`astc`	ASTC texture file. Direct container for ASTC compressed data.
`ktx`	Khronos Texture. Standard container for OpenGL ES textures.
`ktx2`	Khronos Texture (Version 2). Newer format with Basis Universal support.
`zktx`	Khronos Texture (gzip compressed). KTX file compressed for smaller storage.
`pvr3`	PowerVR Texture Format. Native format for iOS and PowerVR GPUs.
`pvr3gz`	PowerVR Texture Format, compressed with gzip. Smaller on disk, decompressed at load time.
`pvr3ccz`	PowerVR Texture Format, compressed with zlib, cocos2d header.

The Image quality can be configured with --astc-quality <0-4>, default value is 2.
For other options (scaling, trimming transparency, ...) have a look at the Image conversion documentation.