Diagnose Image Conversion Problems by Stage
The last visible error is not always the root cause. Identify the final stage that completed successfully, then investigate the next boundary.
Stage map
| Stage | Evidence | Typical cause |
|---|---|---|
| Selection | File never enters list | Browser input policy or detected mismatch |
| Upload | Transfer does not complete | Network or byte limit |
| Validation | Type/route rejected | Extension, MIME, signature, or unsupported direction |
| Decode | Safe conversion error | Corruption, variant, dimensions, frames |
| Encode | Source opens but output fails | Destination limitation or output ceiling |
| Download | Conversion succeeds, file unavailable | Expired or interrupted transfer |
| Destination | File downloads but app rejects it | Receiver compatibility or changed property |
Controlled test
- Record the exact route, file, time, browser, and message.
- Try one small known-good file of the same source type.
- Keep the route unchanged.
- Then keep the original source and change only the destination.
- Compare which boundary moves.
This isolates file-specific failure from route-specific failure without random retries.
Stage-specific tests
Selection and upload
Choose the same file through the picker rather than drag-and-drop, then test a small known-good file. If selection works but transfer does not, inspect network interruption and byte limits.
Validation and decode
Compare the detected signature with the selected source. If labels agree, test whether a maintained local decoder parses the complete image. A thumbnail alone is not proof.
Encode and delivery
Keep the source constant and choose another supported output. Success isolates the original destination or its output size. If conversion succeeds but download fails, examine delivery separately.
Destination use
Open the result in two viewers and verify media type, dimensions, alpha, and frames. An import failure after successful decoding is usually compatibility, not source corruption.
Do not confuse symptoms
A valid file can be unsupported; an invalid file can have the correct extension; a successful output can still be wrong for its destination. Use content-based identification, then consult current format limits.
Escalation record
When reporting a reproducible problem, include the source format reported by a trusted inspector, dimensions, compressed bytes, frame/page count, requested output, exact message, and whether a known-good control succeeded. Do not send confidential originals unless the support process explicitly protects them.