I'm getting a bitmap font on \mathbb{1} when I use the bbold package. After much searching on bitmap fonts specifically in relation to the bbold package, these articles are the closest I've got to a solution:
\mathbb{Z} is not displayed correctly
Image quality of pdf file generated from latex
However, they don't quite answer my problem. The best advice in the first is to use amssymb, which doesn't work in my particular case because amssymb renders \mathbb{1} as something else entirely (not a blackboard "1"). The second article is a bit general but does suggest the lmodern package, which still doesn't solve the problem.
Note also that I've already installed the cm-super font (using MiKTeX), as many other articles suggest.
Here's my code:
\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{bbold}
\begin{document}
This is a test: $\mathbb{1}$.
\end{document}
Here's a fragment (the important bit) of the output:
As the image shows, only the \mathbb{1} is a problem.

bbold-type1: http://miktex.org/packages/bbold-type1 – egreg Nov 13 '15 at 23:09updmap, see http://tex.stackexchange.com/questions/33608/how-to-run-updmap-sys-after-installing-cm-super – egreg Nov 13 '15 at 23:15