Seshat 1.8.4 gives one total ink number, spot colours included, from check to plates

A customer should see one total ink number, and it should be the ink that really goes on the paper. Seshat 1.8.4 makes the check and the plates give exactly that number.

What changed

• Total ink is all printing inks: CMYK and spot colours, added up from the separated page, with overprint as it prints. Technical colours (cut, crease, white, varnish, foil) are not ink and are left out.
• The check and the plates agree. Both separate the page through the file's own output intent and measure the most ink held over about a millimetre inside the printed area. total_ink_highest_percent in plates is the number the check compares with the order's limit.
• Pictures in RGB count as they will print. They are measured through the print profile, as they will be separated. Some files therefore show a slightly higher, truer total than before.
• Reduce ink counts spot inks. In a colour that mixes process and spot inks, the spot inks stay as they are, and cyan, magenta and yellow make room for them.
• Reduce ink says what it could not do. Where separate objects overprint each other above the limit, such as a spot gradient over a heavy CMYK shape, no single colour can be lowered. The answer says partly and gives those places, and the check finds the same ones.

Nothing changes in your code. reduce_ink now also answers result (under_limit or partly) and, when needed, remaining.