A PDF page describes a coordinate space in points rather than a fixed bitmap. Rasterization chooses a scale and asks a renderer to paint that visible page into a finite pixel grid. PageRaster exposes 96, 150 and 300 pixels per PDF inch so the choice and resulting width and height remain reviewable.
From 72 points to one inch
PDF uses 72 points per inch for this scale calculation. The renderer viewport uses scale PPI divided by 72. A 612 by 792 point page at 150 PPI therefore plans 1275 by 1650 pixels. PageRaster floors the positive viewport dimensions to Canvas integers and applies the page crop box and declared rotation before showing the plan. The number is a raster scale, not preserved source DPI or a print-quality certificate.
Plan dimensions before rendering
Higher PPI increases both axes, so pixel area and memory grow roughly with the square of the scale. PageRaster measures every selected page first and stops before rendering if one side exceeds 8192 pixels, one page exceeds 12 million pixels or the selection exceeds 36 million pixels. These bounds keep the browser task finite. Choose the smallest profile that produces the exact measured dimensions your destination needs, then inspect the real output rather than inferring quality from a label.
Verify the downloaded pixels
Open every downloaded PNG or JPEG in the application that will use it, confirm the page number and measured width and height, and compare visible text, fonts, colours, transparency and annotations with the authoritative PDF. Keep the PDF as the source. Raster output is a browser-rendered snapshot, not proof of vector, print, archival, accessibility, legal or semantic equivalence.