ImageMagick convert pdf to jpeg has poor text quality after upgrading ImageMagick version to 6.7.8

Question

After upgrading ImageMagick text quality got degraded when convert pdf to jpeg:

Old image

Answer 1

PDF files are vector files and have no specific size. Their size is controlled by defining the density and units before reading in the PDF file. You can get better quality for the same desired output file size by supersampling. That means rasterize the PDF to a large size and then resize to your desired actual size. For example in ImageMagick:

convert -units pixelsperinch -density 288 image.pdf -resize 25% output.jpg

The nominal density if left off is 72 dpi. So 72*4=288. Then resize by 1/5=25% gets back to the same default size, but should look much better. Change the density or resize to deal with quality and final size as desired.