eschutho commented on PR #39285:
URL: https://github.com/apache/superset/pull/39285#issuecomment-4626701339

   ## QA Verification — High-DPI Chart Image Download
   
   **Commit tested:** \`50a33ae199dd456189ae8e221ffb8bd69f3ff50c\`
   **Environment:** Headless Chromium, viewport 1440×900, \`devicePixelRatio=1\`
   **Result: ✅ PASS**
   
   ### What was tested
   
   Loaded the "Misc Charts" dashboard, triggered the chart image download via 
the More Options → Download menu, and measured the pixel dimensions of the 
downloaded JPEG.
   
   ### Measured dimensions
   
   | | Width | Height |
   |---|---|---|
   | Chart visible area (CSS px) | 416 px | 520 px |
   | Clone rendered size (what dom-to-image captures) | 448 px | 567 px |
   | **Downloaded image (this PR)** | **896 px** | **1134 px** |
   | Expected master output (no scale param) | ~448 px | ~567 px |
   
   `IMAGE_DOWNLOAD_SCALE = Math.max(devicePixelRatio=1 || 1, 2) = 2`
   Scale applied: 896 / 448 = **2.000×**, 1134 / 567 = **2.000×** — exactly 2×.
   
   ### Screenshots
   
   Dashboard with chart visible:
   
![Dashboard](https://raw.githubusercontent.com/eschutho/superset/image-download-scale-pr/qa-evidence/pr39285-dashboard.png)
   
   Download submenu open:
   ![Download 
menu](https://raw.githubusercontent.com/eschutho/superset/image-download-scale-pr/qa-evidence/pr39285-download-menu.png)
   
   The actual downloaded JPEG (896×1134 px — 2× the clone's 448×567 px rendered 
size):
   ![Downloaded chart 
image](https://raw.githubusercontent.com/eschutho/superset/image-download-scale-pr/qa-evidence/pr39285-downloaded-image-896x1134.jpg)
   
   ### Notes
   
   - The clone's rendered size (448×567) is slightly larger than the visible 
CSS area (416×520) because `createEnhancedClone()` calls 
`processCloneForVisibility()` which removes `maxHeight` constraints, expanding 
overflow content. The 2× scale is applied correctly against the clone's actual 
dimensions.
   - On a Retina display (dpr=2), `Math.max(2, 2) = 2` — same scale, which 
means the output is always 2× regardless of display density. Intended behavior.


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