CMYK MagickColor strange behaviour

[zomeo]

Hi everyone,

I have a simple Gray image and I want to convert it to CMYK and use the opaque method to fill the rectangle.
My CMYK color should be: C:50 M:9 Y:98 K:61.
The image is here:
https://www.dropbox.com/s/22bq0clwrb3xo ... 0C%29?dl=0

My code:

Code: Select all

MagickImage miPantone1 = new MagickImage(@"E:\CMYK+4SPOT.pdf (PANTONE 371 C)");
miPantone1.Transparent(MagickColors.White);
miPantone1.ColorSpace = ColorSpace.CMYK;
miPantone1.Opaque(MagickColors.Black, new MagickColor(128,23,250,156,255));
miPantone1.Write(@"E:\out.tiff");

I open the TIFF with Photoshop and the box with the following CMYK percentages: C:77 M:99 Y:0 K:4.
I tried every possible combination.
I also tried CMYKColor with bytes and Percentages but the result is always wrong.

I'm using .NET 4 Q8 x64 version.

If I process the same command with magick.exe command line:

Code: Select all

magick "CMYK+4SPOT.pdf (PANTONE 371 C)" -transparent White -set colorspace CMYK -fill cmyk(128,23,250,156) -opaque cmyk(0,0,0,0) out.tiff

the resulting TIFF is OK.

What am I doing wrong?

Thank you,

Denis

[dlemstra]

-set colorspace is not the same as .Colorspace. Your command would translate to this:

Code: Select all

using (MagickImage miPantone1 = new MagickImage("CMYK+4SPOT.pdf (PANTONE 371 C)"))
{
    miPantone1.Transparent(MagickColors.White);
    miPantone1.SetAttribute("colorspace", "CMYK");
    miPantone1.Opaque(new MagickColor("cmyk(0,0,0,0)"), new MagickColor("cmyk(128,23,250,156)"));
    miPantone1.Write("out.tiff");
}

[zomeo]

Thank you dlemstra, it works like a charm.

Best regards,

Denis

[zomeo]

Hello dlemstra,

I did other tests and sometimes it works and sometimes not.
The link to the image:
https://www.dropbox.com/s/6dzz0xrh7fpho ... 0C%29?dl=0

I tried this code:

Code: Select all

using (MagickImage miPantone1 = new MagickImage("CMYK+4SPOT.pdf (PANTONE 371 C)"))
                    {
                        miPantone1.Transparent(MagickColors.White);
                        miPantone1.Write("1.tiff");
                        miPantone1.SetAttribute("colorspace", "CMYK");
                        miPantone1.Write("2.tiff");
                        miPantone1.Opaque(MagickColors.White, new MagickColor("cmyk(128,23,250,156)"));
                        miPantone1.Write("3.tiff");
                    }

The file "1.tiff" is correct. It's a transparent tiff with a black box.
The file "2.tiff" has been modified and the black box became a white box (CMYK 0,0,0,0). It's a strange behaviour because a black box should remain black. But the file is correctly a CMYK file.
For the 3.tiff, the opaque command instead of generating a dark green box (like the PANTONE specification (CMYK(50,9,98,61)) is a violet box (CMYK(77,99,0,4); I used MagickColors.White because of the previous color inversion.

I've also tried to replace MagickColors.White with new MagickColor("cmyk(0,0,0,0)") and in that case the Opaque command does nothing.

What am I doing wrong? How can I obtain a correct dark green box with the correct percentages of CMYK?

I also tried this that seems to work a little well (the 2.tiff is correct now. It remains Black):

Code: Select all

using (MagickImage miPantone1 = new MagickImage("CMYK+4SPOT.pdf (PANTONE 371 C)"))
                    {
                        miPantone1.Transparent(MagickColors.White);
                        miPantone1.Write("1.tiff");
                        miPantone1.ColorSpace = ColorSpace.CMYK;
                        miPantone1.Write("2.tiff");
                        miPantone1.Opaque(MagickColors.Black, new MagickColor("cmyk(128,23,250,156)"));
                        miPantone1.Write("3.tiff");
                    }

but the result of the Spot color is the same.
I also tried to use ColorCMYK as Color, with 0-255 range for colors and with percentages. The resulting color conversion is always the same. It seems that something RGB happens in the behind.

Thank you

Denis

[dlemstra]

It appears you found a bug. The second block of code should work. I just pushed a patch to fix this issue. Will try to publish a new release this weekend.

[zomeo]

Thank you very much dlemstra.

[zomeo]

Hello Dirk,

with the latest version the problem is solved.

Thank you,

Denis