When including images in XeTeX using \XeTeXpicfile I noticed that the dimensions of the output picture are wrong. I created the following MWE:
\nopagenumbers
% The TeXbook, p. 311
\def\hidehrule#1#2{\kern-#1%
\hrule height#1 depth#2 \kern-#2 }
\def\hidevrule#1#2{\kern-#1{\dimen0=#1
\advance\dimen0 by#2\vrule width\dimen0}\kern-#2 }
\def\makeblankbox#1#2{\hbox{\lower\dp0\vbox{\hidehrule{#1}{#2}%
\kern-#1 % overlap the rules at the corners
\hbox to \wd0{\hidevrule{#1}{#2}%
\raise\ht0\vbox to #1{}% set the vrule height
\lower\dp0\vtop to #1{}% set the vrule depth
\hfil\hidevrule{#2}{#1}}%
\kern-#1\hidehrule{#2}{#1}}}}
\def\pic#1{\setbox0=\vbox{\XeTeXpicfile #1 width 8cm}
\vbox{\leavevmode\copy0\kern-\wd0\makeblankbox{.25pt}{.25pt}}}
\pic{test-cmyk300.jpg}
\bigskip
\pic{test-cmyk72.jpg}
\bigskip
\pic{test-rgb300.jpg}
\bye
Please download test-cmyk300.jpg, test-cmyk72.jpg and test-rgb300.jpg and watch the XeTeX output. (Side note: this is a detail of The Haywain Triptych.)
You'll notice that the 300 DPI CMYK image is enlarged, even though the parameter width 8cm is given. A workaround is to set the image resolution to 72 DPI, in which case the size is exactly right. Using a lower DPI setting the image is also scaled down. This problem doesn't exist with RGB images.
Is this a bug in XeTeX?
xdvipdfmxrather than XeTeX: I do see the erroneous behaviour here.