I have run into an issue exporting a PDF file from the Map Composer in QGIS (Essen v 2.18.2, Qt ver 4.8.6) running on macOS Sierra (os ver. 10.12.4). The export resolution is set to 600 DPI (the same problem occurs with 300 DPI). The page size is A1 (210 by 297 cm). The map in the composer contains some minimal furniture (title, key, labeling) and a single map object displaying a raster LiDAR image. When exported to PDF (and to PNG) the resulting map is fuzzy, including all of the map furniture. I have tried with export raster selected and deselected. Same result. If I use the print system to export a PDF, the printer driver, of course, rejects the A1 page size and produces a crop Letter-sized rendering of the upper left corner of the map. I have reread the manual and searched the web to no avail. Does anyone have any suggestions or is this a bug in the current version of QGIS?
On a side note if the resolution is set any higher than 600 DPI, QGIS exports a single byte PDF file.