[Dev-luatex] problems with the mediabox

Peter Rolf indiego at gmx.net
Fri Sep 18 12:42:44 CEST 2009


I still have preflighting problems with the mediabox of luatex. It's 
accuracy is sufficient for printing, but using the values for a 
preflight is troublesome.
An example: if I define a A4+ paper (303mm x 216mm) I get a mediabox of 
303.0mm x 215.999mm. Hans has already restricted the trailing numbers of 
the trimbox/cropbox values in ConTeXt to adapt the accuracy (else 
rounding of the mediabox can lead to a bigger trim|cropbox, which is 
against definition). Anyhow, this is not enough for this example:

MediaBox (mm): 303.0x215.999 (0.0/0.0/303.0/215.999)
CropBox  (mm): 303.0x216.0   (0.0/0.0/303.0/216.0  )
TrimBox  (mm): 303.0x216.0   (0.0/0.0/303.0/216.0  )

MediaBox < CropBox|TrimBox

So using the same number of digits after the point (%.3f) does not solve 
the problem.

Setting the width to 216.001mm in this example helps, but this is 

MediaBox (mm): 303.0x216.0023  (0.0/0.0/303.0/216.0023 )
CropBox  (mm): 303.0x216.00101 (0.0/0.0/303.0/216.00101)
TrimBox  (mm): 303.0x216.00101 (0.0/0.0/303.0/216.00101)

If you use some bleeding offset (in the A4+ example normally 3mm on each 
side) the problem vanishes. But for PDF/X you have to set the 
crop-|trimbox anyway, regardless if you use a bleeding offset or not.

Possible solutions:
- read access to the mediabox values, so that rounding errors can be handled
- use the same calculation routine for all pdf boxes (e.g. a luatex 
library function)
- ??

Any comments are welcome.

Best wishes,  Peter

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