[PierreRaybaut]

Closes #74

Summary

Since v0.6.1 (8d6f1f1), the uniform-image bitmap is a Plotly layout image, which the browser smooths whenever it is enlarged: zoomed-in pixels fade into each other. The former image trace avoided it (zsmooth: false → image-rendering: pixelated, or a magnified canvas on Safari and in exports), and DataLab desktop shows the nearest pixel by default.

• Integer magnification of the bitmap (imageLod.ts, imageRaster.ts): when zoomed in (at least two device pixels per image pixel), the raster plan gets zoomX/zoomY factors (floor(display budget / visible pixels), within the 2048-pixel cap). The window is painted 1:1 as before, then copied onto the magnified canvas with imageSmoothingEnabled = false: every pixel is a sharp block, in every browser and in exported PNG images (modebar download, AI assistant capture). Small images are magnified whole when they fit, so panning never uncovers unpainted areas; otherwise only the visible window is painted, as for large images. The bitmap placement is unchanged (physical cell size).
• CSS finishing touch (styles.css): image-rendering: pixelated (Plotly's declaration list) on the layout images of a view, set only while its bitmap shows undecimated pixels enlarged on screen (showsCrispPixels). The small remaining enlargement then stays sharp on Chrome, Edge and Firefox. Measured in Chromium: pixelated also samples to the nearest pixel when downscaling (a fine checkerboard turns black instead of mid-grey), so it is never set on reduced or decimated bitmaps.
  • image viewer (and the Create ROI grid… preview): from the measured plot size and view;
  • Spatial view: when every visible bitmap qualifies (typically when zoomed into one image);
  • processing preview (plot size not tracked): when the bitmap is magnified.
• Always nearest pixel, like DataLab desktop's default; no new setting.
• Changelog entry.

Not affected: thumbnails (already pixelated), non-uniform images and the profile dialog (Plotly heatmaps drawn at screen resolution).

Validation

• vitest: 947 passed. New tests cover the magnification factors (DPR, two-pixel threshold, cap, independent axes), raster planning (whole/windowed/1:1), the magnified canvas (drawImage without smoothing, fallback without a 2D context), showsCrispPixels (magnified, slightly enlarged, reduced, decimated, DPR), and the CSS class in the image viewer and the spatial view.
• Playwright (chromium): image-lod (including a new checkerboard test: integer magnification, a bitmap with exactly two colours, computed image-rendering: pixelated, and a screen row with only the two colours; the new test fails on the base branch), image-pan, image-roi-drag, multi-image-spatial: 10 passed.
• Browser check on a zoomed 4×4 image: sharp pixels on screen and in a Plotly.toImage export.
• tsc, eslint, prettier clean; npm run build within the bundle budget.
• Raster cost measured in Chromium: magnifying and encoding a 2048² bitmap takes 20–55 ms (debounced 80 ms, as before).
• Firefox and WebKit are not installed for Playwright here; the canvas magnification does not depend on the CSS, which only refines the result.

[PierreRaybaut]

CI does not trigger automatically on a PR stacked on another branch: the full \ ests\ workflow was dispatched on \ix/image-viewer-crisp-pixels\ and passed (vitest, pytest 3.11/3.12, the 4 Playwright shards): https://github.com/DataLab-Platform/web/actions/runs/40203589859