Quote:
Originally Posted by RandomTroll
It is clear.
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I think it is evident that we have a different definition of clarity.
Quote:
Originally Posted by RandomTroll
It was a follow-up question to test the hypothesis. A responder said it was the alpha channel. To test that hypothesis ...
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You keep saying that yet your statement bears little credibility. You were quite insistent that you wanted an
automated, non-X solution. This hard requirement does not make sense for diagnostic purposes.
Be that as it may, after some research I do not think that there is an alpha channel to begin with, even though there are four channels. I found this
specification. Pay attention to section 6 (6.5.3 in particular) and 7:
Code:
...
6.5.3 APP14 marker segment for colour encoding
A marker segment containing an APP14 marker and the first six bytes of the application data APi (for i = 1 to 6) of the
segment coded as X'41', X'64', X'6F', X'62', X'65', X'00' (the zero-terminated string "Adobe", according to
Rec. ITU-T T.50 or ISO/IEC 646 coding) shall identify an APP14 marker segment for colour encoding. AP12 is assumed
to contain a single-byte transform flag as defined below; the rest of the marker segment is ignored.
Transform flag values of 0, 1 and 2 shall be supported and are interpreted as follows:
0 * CMYK for images that are encoded with four components in which all four CMYK values are
complemented; RGB for images that are encoded with three components; i.e., the APP14 marker does not
specify a transform applied to the image data.
1 * An image encoded with three components using YCbCr colour encoding.
2 * An image encoded with four components using YCCK colour encoding.
...
7 Conversions between colour encodings
Conversion between the RGB and YCbCr colour encodings uses the process specified in Rec. ITU-T T.871 |
ISO/IEC 10918-5.
YCCK is obtained from CMYK by converting the CMY channels to YCC channels using the process specified in
Rec. ITU-T T.871 | ISO/IEC 10918-5 for conversion of RGB channels to YCbCr, but with C (Cyan) substituted for
R (Red), M (Magenta) substituted for G (Green), and Y (Yellow) substituted for B (Blue); the first C of YCCK is the
value Cb and the second C of YCCK is the value Cr that result from that process. The K value in YCCK is computed by
complementing the black channel value in CMYK.
I also found
this thread (unrelated to ImageMagick) which deals with inverted colours in a JPEG. I only gave it a cursory look but it seems that an APP marker is being ignored/misinterpreted which results in inverted colours.
My best guess at this point is that something similar might be happening with ImageMagick but I am not sure. Again, it is probably best to contact the developers about this issue. I am not going to spent any more time on this case.
