On Thu, 5 Jan 2017 23:47:00 -0500
Cesar Romani <cesar.rom...@gmail.com> wrote:

> The quality of the rotated pdfs, which are images, drops off a little.
> For example, some characters are not so sharp as in the original pdf.
> 
> If I use GraphicsMagick I would remedy this with the parameter
> -density as in:
> gm convert -density 300x300 original.pdf -rotate 45 rotated.pdf

From the web:

"A PDF file does not have a density anyway. IM will apply a default
interpretation of 72dpi unless you override it (e.g. -density 300x300
-units pixelsperinch)."


Testing:

convert original.tif -rotate 45 rotated.png

keeps the original density.

1) original.tif was 6000x6000; rotated.png is 8488x8488 (2400dpi)
2) converting to rotated.tif fails
convert: TIFF: negative image positions unsupported rotated.tif @ 
error/tiff.c/WriteTIFFImage/3609.
3) converting to rotated.pdf does produce a much reduced resolution image.

Indeed, PDF is container, not the best format for manipulating bitmap images.
I take two approaches to this:
1) I manipulate/modify the images explicitly "upstream" before including them 
in ConTeXt,
   using any of my favorite tools; or
2) I manipulate/modify the images using MetaPost, within ConTeXt.
   This gives very satisfactory results and does not rely on ImageMagik.

Alan
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