As Ingram Spark and Ingram Lightning Source both require either PDF/X-1a:2001 or PDF/X-3:2002, for print book interiors and covers, it would be really nice if GIMP could export to one of these formats.
Why?
PDF/X-3:2002, allows CMYK, spot, calibrated (managed) RGB, CIELAB, with ICC Profile, based on PDF 1.3.
Not sure if this is helpful, but Scribus can export to PDF/X-1a (without the mention :2001) and PDF/X3 (without the mention :2002 CMYK).
1 Like