Texture compression formats for platform-specific overrides

While Unity supports many common image formats as source files for importing your Textures (such as JPG, PNG, PSD and TGA), these formats are not used during realtime rendering by 3D graphics hardware such as a graphics card or mobile device. 3D graphics hardware requires Textures to be compressed in specialized formats which are optimised for fast Texture sampling. The various different platforms and devices available each have their own different proprietary formats.

By default, the Unity Editor automatically converts Textures to the most appropriate format to match the build target you have selected. Only the converted Textures are included in your build; your source Asset files are left in their original format, in your project’s Assets folder. However, on most platforms there are a number of different supported Texture compression formats to choose from. Unity has certain default formats set up for each platform, but in some situations you may want to override the default and pick a different compression format for some of your Textures (for example, if you are using a Texture as a mask, with only one channel, you might choose to use the BC4 format to save space while preserving quality).

To apply custom settings for each platform, use the Texture Importer to set default options, then use the Platform-specific overrides panel to override those defaults for specific platforms.

The following table shows the default formats used for each platform.

All supported Texture compression formats

The following table shows the Texture compression format options available on each platform, and the resulting compressed file size (based on a 256px-square image). Choosing a Texture compression format is a balance between file size and quality; the higher the quality, the greater the file size. In the description below, see the final file size of a in-game Texture of 256 by 256 pixels.

When you use a Texture compression format that is not supported on the target platform, the Textures are decompressed to RGBA 32 and stored in memory alongside the compressed Textures. When this happens, time is lost decompressing Textures, and memory is lost because you are storing them twice. In addition, all platforms have different hardware, and are optimised to work most efficiently with specific compression formats; choosing non-compatible formats can impact your game’s performance. The table below shows supported platforms for each compression format.

Notes on the table below:

• RGB is a color model in which red, green and blue are added together in various ways to reproduce a broad array of colors.

• RGBA is a version of RGB with an alpha channel, which supports blending and opacity alteration.

• Crunch compression is a lossy compression format (meaning that parts of the data are lost during compression) on top of DXT Texture compression. Textures are decompressed to DXT on the CPU, and then uploaded to the GPU at runtime. Crunch compression helps the Texture use the lowest possible amount of space on disk and for downloads. Crunch Textures can take a long time to compress, but decompression at runtime is very fast.

You can import Textures from DDS files, but only DXT, BC compressed formats, or uncompressed pixel formats are supported.

Notes on Android

Unless you’re targeting specific hardware (such as Tegra), ETC2 compression is the most efficient option for Android, offering the best balance of quality and file size (with associated memory size requirements). If you need an alpha channel, you could store it externally and still benefit from a lower Texture file size.

You can use ETC1 for Textures that have an alpha channel, but only if the build is for Android and the Textures are placed on an atlas (by specifying the packing tag). To enable this, tick the Compress using ETC1 checkbox for the Texture. Unity splits the resulting atlas into two Textures, each without an alpha channel, and then combines them in the final parts of the render pipeline.

To store an alpha channel in a Texture, use RGBA16 bit compression, which is supported by all hardware vendors.