Sparse color barycentric example

[pgajdos]

magick -size 100x100 xc:none -draw "polygon 30,10  10,80  90,90" \
          -colorspace RGB \
          -sparse-color Barycentric '30,10 red   10,80 blue   90,90 lime' \
          -colorspace sRGB   sparse_bary_triangle_2.png

does not produce colorful triangle on white background:

https://usage.imagemagick.org/canvas/sparse_bary_triangle_2.png

but colorful canvas:

I tried several versions of ImageMagick, e. g. 7.1.1-43 or 7.0.7-34 with same result. I tried also 6.8.8.1 and expected triangle was produced indeed.

[dlemstra]

Why did you open the issue here? What are you seeing where?

[pgajdos]

Why did you open the issue here?

Should I open the issue in some other category? 'Barycentric' example in https://usage.imagemagick.org/canvas/ does not work as I would expect reading the example doc.

What are you seeing where?

Not sure I understand.

[dlemstra]

This is the repository for the Freds-Scripts and not our Usage website. I will move this.

[pgajdos]

I see, thanks.

[fmw42]

You are using the wrong example from https://usage.imagemagick.org/canvas/#barycentric

Try

magick -size 100x100 xc: -colorspace RGB \
          -sparse-color Barycentric '30,10 red   10,80 blue   90,90 lime' \
          -colorspace sRGB  -fill white -stroke black \
          \( -size 100x100 xc:black -draw 'polygon 30,10  10,80  90,90' \) \
          -alpha off -compose CopyOpacity -composite \
          -draw 'circle 30,10 30,12  circle 10,80 10,82  circle 90,90 90,92' \
          sparse_bary_triangle.png

Which produces a colorful triangle on transparent background.

You were using the code for the example above this that makes a full colorful image.

[pgajdos]

Thanks, Fred, that is true.

However my concern is, that the creation of sparse_bary_triangle_2.png in the doc does not produce the documented result as I understand, is that correct?

[fmw42]

Which example are you really using? Both examples produce the correct image as shown on his page if you remove the examples from the page and view them in a viewer that supports transparency (for the second image).

The first example produces the full colorful image as he shows.

The second example produces a triangle on transparent background. It looks white because it is displayed on the page on a white background (which shows through the transparency).

Please clarify which example you are complaining about and what image you get?

[pgajdos]

I am sorry, I do not probably understand and do not know how to rephrase my initial comment. I basically run the command from there (taken from https://usage.imagemagick.org/canvas/) to create sparse_bary_triangle_2.png, as the doc says. Instead of https://usage.imagemagick.org/canvas/sparse_bary_triangle_2.png I get the image in my initial comment.

[pgajdos]

I am sorry for these four issues we have found. Anyway, thanks to all (Fred, Anthony, Dirk, Christy, ...) for this great documentation.

[fmw42]

Sorry, my mistake. I do get your result, which does not match the posted example. I will look into it, but I suspect something changed since that was posted.

[fmw42]

The example works in IM 6 (as when created). But due to changes for IM 7, it needs a slight modification due to how the alpha channel is processed.

IM 6

convert -size 100x100 xc:none -draw "polygon 30,10  10,80  90,90" \
          -colorspace RGB \
          -sparse-color Barycentric '30,10 red   10,80 blue   90,90 lime' \
          -colorspace sRGB   sparse_bary_triangle_2.png

IM 7

magick -size 100x100 xc:none -draw "polygon 30,10  10,80  90,90" \
          -colorspace RGB -channel rgb \
          -sparse-color Barycentric '30,10 red   10,80 blue   90,90 lime' \
          -colorspace sRGB   sparse_bary_triangle_2.png

Both generate:

[pgajdos]

Fred, awesome, -channel rgb did it.

Thank you!