Example: MINC2 Round Trip

This example constructs a deterministic 9 × 64 × 64 MR-like phantom with an off-center lesion, asymmetric marker, slice-dependent texture, anisotropic spacing, nonzero origin, and a non-identity direction matrix. It writes and reads the volume through write_minc and read_minc.

How to read the figure

The source and decoded panels use the same display range [0, 1200]. They are expected to look identical, but appearance is not the correctness test. The third panel is a direct bitwise comparison:

• dark blue means the source and decoded f32 bits match;
• red would mark a corrupted voxel;
• the displayed mismatch count and maximum absolute error are computed from the actual central slices.

The executable also compares every voxel and every geometry field over the complete volume before writing the SVG. A wrong shape, axis order, origin, spacing, direction, or value stops generation.

The lower panel is intentionally different. It writes a second, foreign-style i16 MINC2 fixture with stored codes [0, 25, 50, 100] in each of two slices. Both slices use valid_range = [0, 100], but their real ranges differ:

• slice 0 maps to [-1000, 1000];
• slice 1 maps to [0, 200].

The displayed decoded rows come from read_minc. They expose the mapping as numbers so the scaling effect cannot be hidden by automatic image contrast.

What crosses the format boundary

The last panel reports the measured file size and the actual source geometry. The payload is one x-fastest contiguous little-endian f32 dataset. Shape, voxel bits, origin, spacing, and direction round-trip exactly in RITK’s current profile. The lower panel separately exercises per-slice quantitative integer scaling. Compression, chunking, patient/study metadata, integer-valued writing through the public writer, and multiresolution images remain outside this example.

The writer converts the 36,864 voxels in 2,048-value chunks. Its conversion scratch remains 8 KiB rather than growing to another 147,456-byte volume-sized buffer.

Run it

From the repository root:

cargo run -p ritk-minc --example book_minc -- \
  docs/book/figures/minc_roundtrip.svg

The .mnc file is temporary. Only the deterministic SVG is retained. The complete source is crates/ritk-minc/examples/book_minc.rs.