Budgeting BC, ASTC, and ETC2 textures on real targets

Budget the uploaded representation

A small source image file does not imply a small GPU allocation. GPU block compression provides bounded random access to groups of texels; distribution compression and container size answer different questions. [2][3] Record the format actually uploaded after importing or transcoding, then inspect its resident allocation on the target device.

Separate storage capacity, transfer size, encoder time, and sampling cost in the budget. A single compression percentage cannot describe all four.

Match formats to supported channels

BC1 stores a 4 × 4 block in 8 bytes; BC5 and BC7 use 16 bytes for that footprint. Their channel capabilities differ, and Direct3D support depends on the format and feature level. [1]

ASTC keeps a 128-bit block while varying its texel footprint, allowing different rates. [2] ETC2/EAC support is part of OpenGL ES 3.0, while other APIs use their own capability mechanisms. The Khronos guide lists specific format and feature checks, including Vulkan compression features. [3] Avoid inferring support merely from a desktop or mobile label.

Calculate rounded block storage

Take an illustrative 2048 × 2048 base texture. BC7 needs 512 × 512 blocks of 16 bytes, exactly 4 MiB. ASTC with a 6 × 6 footprint requires rounding each dimension up to 342 blocks: 342 × 342 × 16 = 1,871,424 bytes, approximately 1.78 MiB.

These are base-level payload sizes, not complete allocations or quality equivalence. Add every mip level with its own block rounding, plus array layers, cube faces, and any platform alignment. A fallback that expands to uncompressed pixels changes the budget again. Keep this arithmetic beside the build's observed texture report.

Compare errors where they matter

Create a small test set containing smooth gradients, sharp alpha boundaries, noisy colour, and normal data. Encode each applicable format at chosen settings, then inspect the imported result under the actual shader. Check normals through moving highlights and masks through their thresholded use; a pleasing RGB preview can hide functional errors.

Vary encoder effort separately from block footprint. Record build time and examine whether improved encoding removes the objectionable artifact before increasing memory for an entire asset category.

Define exceptions deliberately

No lossy format is ideal for every signal. Fine text, binary masks, and unusually sensitive material channels may justify a different format or resolution. Preserve a clear exception rule and verify that platform fallbacks implement it.

Ship the smallest tested representation that meets the visual requirement on supported targets. Recheck the uploaded format whenever the importer, transcoder, or deployment platform changes.

Sources

• [1] Texture Block Compression in Direct3D 11 — Microsoft.
• [2] ASTC Format Overview — Arm.
• [3] KTX Developer Guide — Khronos Group.