Reading an IntegerPixel grayscale image from memory

[kevin.mcguinness]

I am trying to read a single channel integer pixel image from memory using the following

Code: Select all

Magick::Image image;
image.read(width, height, "K", Magick::IntegerPixel, data);
...
image.write("out.png");

The in memory image is a label mask, that usually contains just a few low pixel values (mostly
zero, a few patches of 1, 2 .. ) however, when saved the image appears as all zero. I tried
saving to the pgm format and also tried image.type(Magick::GrayscaleType) and
image.colorSpace(Magick::GRAYColorspace) but to no avail. Anyone have any idea what's wrong
here? Im using imagemagick 6.2.4

Thanks,
Kevin

[kevin.mcguinness]

Actually this happens with char pixels too.. Just to clarify,
why does this piece of code produce a black image instead of
a white one?

Code: Select all

  // Build an in memory grayscale image
  int w = 100, h = 100;
  int s = w * h;
  std::vector<uint8_t> im(s);

  // Make all pixels white
  for (int i = 0; i < s; i++) im[i] = 255;

  try {
    // Load it into imagemagick
    Magick::Image m;
    m.read(w, h, "K", Magick::CharPixel, &im[0]);

    // Save it as a png
    m.write("test.png");

  } catch (Magick::Exception& ex) {
    cout << ex.what() << endl;
  }

[magick]

Try "G" instead of "K". "K" is the black channel whereas "G" is grayscale.

[kevin.mcguinness]

Excellent, this works

Isn't "G" also the green channel? Wish that was in the documentation...

[kevin.mcguinness]

Actually, this only worked for the pure white image

If i use the same code to make a pure black image (im = 0), then
using "G" a pink image is produced. If i call m.type(Magick::GrayscaleType)
before read() i get a white image, if i call it after i get a gray image

Whats going on?

[magick]

Doh! Not "G", its "I" for intensity. You are right, "G" is for green.

[kevin.mcguinness]

Fantastic, thanks!