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Correct RECO output timestamps and complex metadata #123

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gdevenyi merged 1 commit into from
Aug 27, 2026
Merged

Correct RECO output timestamps and complex metadata #123

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25 changes: 21 additions & 4 deletions FILE_FORMAT.md
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Expand Up @@ -1996,15 +1996,32 @@ These are filled by the reconstruction and describe the output:

| Parameter | Type | Description |
|-----------|------|-------------|
| `RECO_minima` | int[] | Minimum scaled 32-bit value per image |
| `RECO_maxima` | int[] | Maximum scaled 32-bit value per image |
| `RECO_minima` | int[] | Minimum value in the scaled 32-bit intermediate data for each reconstructed image |
| `RECO_maxima` | int[] | Maximum value in the scaled 32-bit intermediate data for each reconstructed image |
| `RECO_map_min` | double[] | Lower bound of mapped range per image |
| `RECO_map_max` | double[] | Upper bound of mapped range per image |
| `RECO_map_offset` | double[] | 0th-order mapping coefficient per image |
| `RECO_map_slope` | double[] | 1st-order mapping coefficient per image |
| `RECO_fov` | double[] | Output field of view in cm |
| `RECO_time` | char[] | Reconstruction timestamp |
| `RECO_abs_time` | int or struct | Reconstruction time. PV5.1 writes a bare Unix-epoch integer; PV6/PV360 write the `pvtime_t` struct form `(seconds, milliseconds, tzMinutes)` — see [Section 2.2](#22-data-types) |
| `RECO_time` | char[24] (PV5.1) / pvtime_t (PV6+) | Optional human-readable date and time when reconstruction started; PV6+ commonly uses the ISO string form of `pvtime_t` |
| `RECO_abs_time` | int (PV5.1) / pvtime_t (PV6+) | Optional reconstruction start time. PV5.1 stores bare Unix seconds; PV6+ stores the `(seconds, milliseconds, tzMinutes)` struct form of `pvtime_t` |

For `COMPLEX_IMAGE`, these output arrays are **not duplicated for the appended imaginary block**.
The manuals specify that scaling, minima and maxima reflect the real images; the imaginary images
reuse the identical scaling, and their extrema are merely assumed to be close matches. Thus an
imaginary frame must use the coefficients of its corresponding real frame, not look for a second
set indexed by the doubled `VisuCoreFrameCount`.

When present, `RECO_time` and `RECO_abs_time` describe the start of reconstruction, not
acquisition or file modification time. Reconstructions that write `RECO_time` pair it with
`RECO_abs_time` in the available PV5.1–PV360 data. They are nevertheless optional: derived
PV360 DTI processings commonly omit `RECO_time` while retaining the three-field
`RECO_abs_time`, and some processings omit both fields.

Their type transition matches the other ParaVision time fields described in §2.2. Although PV6
D02 and the PV360 manuals retain the older descriptions “char array” and “int … Unix format”,
the PV6.0.1 headers and stored files use `pvtime_t` for both fields. Dispatch by the encoded value
form; do not require either field or the legacy scalar integer in a PV6+ file.

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