When the PDF-RIP engine rasterizes a page it goes through a number of stages (interpreting, flattening, rasterizing, ...)
Flattening is the process of planarizing overlapping drawing objects into non-overlapping areas and then replacing the original overlapping objects with new, abutting drawing objects (one per area).
Another method of flattening is Global Rasterization. This procedure uses a pixel-to-pixel color blending.
The standard hybrid flattening provides good performance in typical jobs because it flattens each region where line art objects overlap in a single color-blending operation. However, planarizing some transparency artwork can require an extremely long time or can exhaust memory. In pages that include such artwork, the time and memory cost of planarizing outweighs the benefit of fewer blending operations and so global rasterization (which avoids planarizing) is preferable.
Open the Settings Editor and navigate to: . See setting [Global rasterization mode].
[Global rasterization mode] = [Auto global rasterization]
Automatically select a flattening mode depending on page complexity; either standard hybrid flattening or global rasterization
[Global rasterization mode] = [Forced global rasterization]
Always uses global rasterization.