Finally got to your images by removing the "local." from your link.
(Also my browser kept telling me it was JPEG, but I forced it to be
PNG when saving it)
However, your image is not boolean transparency (see last line of
histogram just below), so PNG8 may force it to be and mess it up.
However, I think you have a bug.
identify -verbose jobs_original.png
Type: GrayscaleMatte
Base type: GrayscaleMatte
Endianess: Undefined
Colorspace: RGB
Depth: 8-bit
Channel depth:
gray: 8-bit
alpha: 8-bit
Channel statistics:
gray:
min: 0 (0)
max: 255 (1)
mean: 164.527 (0.645204)
standard deviation: 118.643 (0.465268)
kurtosis: -1.5896
skewness: -0.602835
alpha:
min: 0 (0)
max: 255 (1)
mean: 186.131 (0.729925)
standard deviation: 111.811 (0.438473)
kurtosis: -0.896707
skewness: 1.03907
Alpha: none #00000000
Histogram:
13342: (255,255,255,255) #FFFFFF white
5634: ( 0, 0, 0, 0) #00000000 none
744: ( 0, 0, 0,255) #000000 black
23: (253,253,253,255) #FDFDFD rgba(253,253,253,1)
21: (254,254,254,255) #FEFEFE rgba(254,254,254,1)
18: ( 1, 1, 1,255) #010101 rgba(1,1,1,1)
18: (251,251,251,255) #FBFBFB rgba(251,251,251,1)
15: ( 3, 3, 3,255) #030303 grey1
14: ( 2, 2, 2,255) #020202 rgba(2,2,2,1)
13: (240,240,240,255) #F0F0F0 grey94
12: (236,236,236,255) #ECECEC rgba(236,236,236,1)
12: (237,237,237,255) #EDEDED grey93
11: ( 63, 63, 63, 2) #3F3F3F02 rgba(63,63,63,0.00784314)
Converting to gif works fine.
convert jobs_original.png jobs_original.gif
But converting to PNG8 does not:
convert jobs_original.png PNG8:jobs_original_png8.png
This seems to work to use GIF as an intermediate with normal PNG:
convert jobs_original.png GIF:- | convert - jobs_original_gif_png.png
identify -verbose jobs_original_gif_png.png
Image: jobs_original_gif_png.png
Format: PNG (Portable Network Graphics)
Class: PseudoClass
Geometry: 256x86+0+0
Resolution: 72x72
Print size: 3.55556x1.19444
Units: Undefined
Type: GrayscaleMatte
Base type: GrayscaleMatte
Endianess: Undefined
Colorspace: RGB
Depth: 8-bit
Channel depth:
gray: 8-bit
alpha: 1-bit
Channel statistics:
gray:
min: 0 (0)
max: 255 (1)
mean: 164.349 (0.644506)
standard deviation: 118.862 (0.466127)
kurtosis: -1.5931
skewness: -0.601093
alpha:
min: 0 (0)
max: 255 (1)
mean: 186.432 (0.731105)
standard deviation: 113.063 (0.443385)
kurtosis: -0.913288
skewness: 1.04245
Alpha: none #00000000
But this does not using PNG8:
convert jobs_original.png GIF:- | convert - PNG8:jobs_original_gif_png8.png
coders/png.c:6990: failed assertion `(unsigned long) packet_index <
number_colors'
Abort trap
Fred
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