I thought adding
-debug "All" -log "%d %f %e "
or
-debug "Coder,Policy" -log "%d %f %e "
Would help you duplicate the calls convert makes, but it is not so helpful on my version (ImageMagick 6.5.6-5 2009-09-25 Q16 OpenMP)
Policy IsRightsAuthorized Domain: Path; rights=Read; pattern
+="somethumb.jpg" ...
Policy IsRightsAuthorized Domain: Coder; rights=Read; patter
+n="JPEG" ...
Policy IsRightsAuthorized Domain: Path; rights=Read; pattern
+="somethumb.jpg" ...
Coder ReadJPEGImage Interlace: nonprogressive
Coder ReadJPEGImage Data precision: 8
Coder ReadJPEGImage Geometry: 105x78
Coder JPEGSetImageQuality Quality: 75
Coder JPEGSetImageSamplingFactor Colorspace: RGB
Coder JPEGSetImageSamplingFactor Sampling Factors: 2x2,1x1,1
+x1
Policy IsRightsAuthorized Domain: Coder; rights=Write; patte
+rn="JPG" ...
Policy IsRightsAuthorized Domain: Path; rights=Write; patter
+n="cnv002.jpg" ...
Coder WriteJPEGImage Image resolution: 72,72
Coder WriteJPEGImage Interlace: non-progressive
Coder WriteJPEGImage Quality: 75
Coder WriteJPEGImage Input sampling-factors=2x2,1x1,1x1
Coder WriteJPEGImage Storage class: DirectClass
Coder WriteJPEGImage Depth: 8
Coder WriteJPEGImage Number of colors: unspecified
Coder WriteJPEGImage JPEG data precision: 8
Coder WriteJPEGImage Image colorspace is RGB
Coder WriteJPEGImage Sampling factors: 2x2,1x1,1x1
