Example: Analyze 7.5 Round Trip

This example writes and reads a deterministic 4 × 64 × 64 f32 volume through the public Analyze API. The phantom contains concentric structures, an off-center marker, a z-dependent diagonal, and a per-slice intensity offset. Those features make axis reversal, slice duplication, and value corruption visible and detectable.

How to read the figure

The first two panels use the same display range [0, 1100]. They should look identical because the writer stores f32 and the reader returns those values without quantization. Similar appearance alone is not the oracle.

The third panel is the explicit comparison:

• dark blue means the displayed source and decoded voxel bits are equal;
• red would identify any mismatch;
• max |decoded − source| = 0 is calculated from the actual slices.

The executable also compares every voxel in all four slices before generating the SVG. A wrong shape, geometry field, slice order, or value stops the example.

Public API

use coeus_core::SequentialBackend;
use ritk_analyze::{read_analyze, write_analyze};

let backend = SequentialBackend;
write_analyze("phantom.hdr", &source, &backend)?;
let decoded = read_analyze("phantom.hdr", &backend)?;

The .hdr file is 348 bytes. For shape [4, 64, 64], the .img payload is 4 × 64 × 64 × 4 = 65,536 bytes. The final panel reports those measured file sizes and the geometry that the format can reproduce under RITK’s convention.

Direction is identity because Analyze 7.5 has no full direction matrix. The chosen origin is an exact integer multiple of spacing on each physical axis; otherwise the originator convention would round it to the nearest voxel.

After producing the figure, the executable appends one byte to the temporary payload and confirms that the reader rejects the trailing data. The malformed pair never becomes an image.

Run it

From the repository root:

cargo run -p ritk-analyze --example book_analyze -- \
  docs/book/figures/analyze_roundtrip.svg

The Analyze pair is temporary. Only the deterministic SVG is retained. The complete source is crates/ritk-analyze/examples/book_analyze.rs.