Function render_separation 

pub fn render_separation(
    doc: &PdfDocument,
    page_num: usize,
    ink_name: &str,
    dpi: u32,
) -> Result<SeparationPlate>

Available on crate feature rendering only.

Render a single ink separation plate for a page.

Returns a grayscale image where pixel intensity = tint percentage of the named ink. If the ink is not present on the page, the plate is all zeros.

This is a thin wrapper over the multi-ink path; if you need every plate on a page, call render_separations instead — it walks the content stream once for all inks together.