Legacy ImageMagick Discussions Archive

convert -units PixelsPerCentimeter -density 37.8 MSVG:wizard.svg tmp1.png
Image: tmp1.png
Format: PNG (Portable Network Graphics)
Mime type: image/png
Class: DirectClass
Geometry: 370x492+0+0
Resolution: 37.8x37.8
Print size: 9.78836x13.0159
Units: PixelsPerCentimeter



convert -units PixelsPerCentimeter -density 37.8 MSVG:wizard.svg tmp1.jpg
Image: tmp1.jpg
Format: JPEG (Joint Photographic Experts Group JFIF format)
Mime type: image/jpeg
Class: DirectClass
Geometry: 370x492+0+0
Resolution: 37x37
Print size: 10x13.2973
Units: PixelsPerCentimeter


Looks like for JPG, the Resolution is being truncated and this affects the print size.

This is still an issue in IM 6.9.10.20 and IM 7.0.8.20

The JFIF resolution marker is integer. To get a fractional resolution you must include an EXIF profile that includes the resolution field. ImageMagick detects this and updates the resolution field with the fractional resolution.

Sorry, I do not understand. When I set the resolution to a fractional value, why does it not adjust the JFIF marker to permit the fractional value?

The JFIF marker only supports 2-byte integer values. EXIF uses 4-byte integers (its divided by 65536) permitting fractional values. See the JFIF format specification.

OK. Thanks