The panel in Lightroom is a running read of the render, so this one reads
the preview blob itself: one downscaled 320px canvas pass bins 256
values per channel, and four SVG paths draw them — the grey luma fill
with the three channel curves screened over it, from absolute black to
absolute white. Dragged by its header, clamped inside the photo, parked
top-right on first paint, and dismissed either from its own frame or from
the toolbar button. It steps aside while the crop frame is up.
3dtours
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