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Posted to notifications@superset.apache.org by "dosubot[bot] (via GitHub)" <gi...@apache.org> on 2026/04/02 16:29:13 UTC
Re: [I] Empty png in report [superset]
dosubot[bot] commented on issue #39070:
URL: https://github.com/apache/superset/issues/39070#issuecomment-4179030992
<!-- Answer -->
This is a recognized pain point — Superset's report validation checks whether the screenshot *capture* returned bytes, but it does **not** verify that the image actually contains meaningful content [[1]](https://github.com/apache/superset/blob/829e4d92d91ceae4b43b1ed3b063ffe45377799c/superset/commands/report/execute.py). A blank/white PNG is still a valid image file, so it passes all checks and gets sent with a green status. That's why you see no errors.
**Why legacy charts make this worse:** Legacy charts have a unique code path where they may lack a saved query context, triggering a fallback screenshot to generate it. This extra step introduces additional failure points that can result in a blank render without raising an error [[1]](https://github.com/apache/superset/blob/829e4d92d91ceae4b43b1ed3b063ffe45377799c/superset/commands/report/execute.py).
**Things to try:**
1. **Replace the legacy bar chart** with the modern ECharts bar chart — this is the most reliable fix if a legacy viz type is the root cause.
2. **Increase screenshot timeout values** in your `superset_config.py`, since charts may not finish rendering before the screenshot is taken:
```python
SCREENSHOT_SELENIUM_HEADSTART = 5
SCREENSHOT_LOCATE_WAIT = 20
SCREENSHOT_LOAD_WAIT = 120
SCREENSHOT_SELENIUM_ANIMATION_WAIT = 10
```
3. **Enable tiled screenshots** if your dashboard is large or has many charts — this addresses a known issue where Chromium unmounts/redraws elements mid-capture on tall pages [[2]](https://github.com/apache/superset/pull/34561):
```python
SCREENSHOT_TILED_ENABLED = True
SCREENSHOT_TILED_CHART_THRESHOLD = 15
SCREENSHOT_TILED_HEIGHT_THRESHOLD = 4000
```
4. **Try Playwright** instead of Selenium, which may be more reliable for screenshot capture:
```python
FEATURE_FLAGS = {
"PLAYWRIGHT_REPORTS_AND_THUMBNAILS": True
}
```
5. **Check your logs for this warning:** `"No query context found, taking a screenshot to generate it"` — it indicates a legacy chart is hitting the fallback path [[1]](https://github.com/apache/superset/blob/829e4d92d91ceae4b43b1ed3b063ffe45377799c/superset/commands/report/execute.py).
As for your core question about *why the report doesn't fail with an error* — this is essentially a gap in Superset's validation. There are related issues tracking this: [#25187](https://github.com/apache/superset/issues/25187) and [#14351](https://github.com/apache/superset/issues/14351). Content-aware validation (detecting blank images before sending) hasn't been implemented yet.
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