convert -geometry 1600x1600 -density 200x200 -quality 100 file.pdf file.jpg
Ao converter para jpg, você pode usar a opção -quality. A "melhor" qualidade seria -qualidade 100.
There is a much simpler way to split multipage pdfs into a jpg:
convert -quality 100 -density 600x600 multipage.pdf single%d.jpg
The -density option defines the quality the pdf is rendered before the convert > here 600dpi. For high quality prints you can increase that number.
The %d just before the jpg suffix is for automatic numbering of the output pages 0,1,2...
The -quality option defines the compression quality of the output jpg (0 min ... 100 max)
The .jpg suffix defines the output format. You could use .png/.jpg/.pdf