I tried to use convert of imagemagick 6.5.6 to make a smaller version from original JPEG file in both file size and geometry. The command I used is:
convert tj/p1.jpg -resize 500x tj/456c2e75fe0faa57fd1cfd87117e0963/p1.jpg
The result is funny, the original is 1102x1542+0+0 in 164kb, the converted one is 500x700+0+0 in 174kb. The pixel count is almost the 20% of the original version, with much bigger file size. So I add -strip options to remove all the verbose information in JPEG profile.
convert tj/p1.jpg -strip -resize 500x tj/500_p1.jpg
The 500_p1.jpg is 500x700+0+0 in 173kb, only 1kb less.
Also I tried to use -thumbnail for it.
convert tj/p1.jpg -thumbnail 500x tj/th/p1.jpg
The thumbed jpeg is 500x700+0+0 in 173kb as well.
Finally I found the -quality can help to reduce images. But 75% quality takes 107kb, 25% quality takes only 50kb with visible loss of detail. But the original quality factor is unknown.
Does anyone have similar issues? Hereafter are the image profiles generated by identify. I found the major differences as following:
Geometry: 1102x1542->500x700 print size: 11x15->5x7 Units: Undefined->PixelsPerInch Quality: unknown->92 Nr. of Pixels: 1.621mb->342kb
Detail of profiles:
Original:
Image: tj/p1.jpg
Format: JPEG (Joint Photographic Experts Group JFIF format)
Class: DirectClass
Geometry: 1102x1542+0+0
Resolution: 100x100
Print size: 11.02x15.42
Units: Undefined
Type: TrueColor
Endianess: Undefined
Colorspace: RGB
Depth: 8-bit
Channel depth:
red: 8-bit
green: 8-bit
blue: 8-bit
Channel statistics:
red:
min: 0 (0)
max: 255 (1)
mean: 218.106 (0.855319)
standard deviation: 52.7336 (0.206798)
kurtosis: 5.04278
skewness: -2.24455
green:
min: 0 (0)
max: 255 (1)
mean: 158.476 (0.621473)
standard deviation: 92.9844 (0.364645)
kurtosis: -1.24112
skewness: -0.535292
blue:
min: 0 (0)
max: 255 (1)
mean: 113.282 (0.444244)
standard deviation: 99.7003 (0.390981)
kurtosis: -1.59582
skewness: 0.278377
Image statistics:
Overall:
min: 0 (0)
max: 255 (1)
mean: 122.466 (0.480259)
standard deviation: 108.274 (0.424604)
kurtosis: -1.78198
skewness: 0.0115088
Rendering intent: Undefined
Interlace: None
Background color: white
Border color: rgb(223,223,223)
Matte color: grey74
Transparent color: black
Page geometry: 1102x1542+0+0
Dispose: Undefined
Iterations: 0
Compression: JPEG
Orientation: Undefined
Properties:
date:create: 2010-10-22T08:35:35+08:00
date:modify: 2010-09-30T10:52:06+08:00
jpeg:colorspace: 2
jpeg:sampling-factor: 2x2,1x1,1x1
signature: cdbd3f63986f0a7c4cd20aedcf9123d91df97e0cb7388f59059b4676fd36d481
Profiles:
Profile-APP12: 15 bytes
Artifacts:
verbose: true
Tainted: False
Filesize: 164kb
Number pixels: 1.621mb
Pixels per second: 20.51mb
User time: 0.078u
Elapsed time: 0:01
Version: ImageMagick 6.5.6-5 2009-09-25 Q16 OpenMP http://www.imagemagick.org
Converted:
Image: tj/456c2e75fe0faa57fd1cfd87117e0963/p1.jpg
Format: JPEG (Joint Photographic Experts Group JFIF format)
Class: DirectClass
Geometry: 500x700+0+0
Resolution: 100x100
Print size: 5x7
Units: PixelsPerInch
Type: TrueColor
Endianess: Undefined
Colorspace: RGB
Depth: 8-bit
Channel depth:
red: 8-bit
green: 8-bit
blue: 8-bit
Channel statistics:
red:
min: 0 (0)
max: 255 (1)
mean: 216.75 (0.849999)
standard deviation: 50.1075 (0.1965)
kurtosis: 4.066
skewness: -2.03195
green:
min: 0 (0)
max: 255 (1)
mean: 158.316 (0.620846)
standard deviation: 89.1433 (0.349582)
kurtosis: -1.17694
skewness: -0.52022
blue:
min: 0 (0)
max: 255 (1)
mean: 113.58 (0.445411)
standard deviation: 96.3298 (0.377764)
kurtosis: -1.53577
skewness: 0.287937
Image statistics:
Overall:
min: 0 (0)
max: 255 (1)
mean: 122.161 (0.479064)
standard deviation: 106.052 (0.415889)
kurtosis: -1.7498
skewness: 0.00808184
Rendering intent: Undefined
Interlace: None
Background color: white
Border color: rgb(223,223,223)
Matte color: grey74
Transparent color: black
Page geometry: 500x700+0+0
Dispose: Undefined
Iterations: 0
Compression: JPEG
Quality: 92
Orientation: Undefined
Properties:
date:create: 2010-10-22T10:27:18+08:00
date:modify: 2010-10-22T10:31:08+08:00
jpeg:colorspace: 2
jpeg:sampling-factor: 2x2,1x1,1x1
signature: 63202ddf9106d3374fe3a396f5105ce8099051cf807ceb2ab5a19532957cec10
Artifacts:
verbose: true
Tainted: False
Filesize: 174kb
Number pixels: 342kb
Version: ImageMagick 6.5.6-5 2009-09-25 Q16 OpenMP http://www.imagemagick.org