Method: Magick::Image#color_histogram

Defined in:

ext/RMagick/rmimage.c

#color_histogram ⇒ Object

Call GetImageHistogram.

Ruby usage:

- @verbatim Image_color_histogram(VALUE self); @endverbatim

Notes:

- returns hash @verbatim {aPixel=>count} @endverbatim

Parameters:

• self —

  this object

Returns:

• a histogram

# File 'ext/RMagick/rmimage.c', line 2504

VALUE
Image_color_histogram(VALUE self)
{
    Image *image, *dc_copy = NULL;
    volatile VALUE hash, pixel;
    unsigned long x, colors;
    ColorPacket *histogram;
    ExceptionInfo exception;

    image = rm_check_destroyed(self);

    // If image not DirectClass make a DirectClass copy.
    if (image->storage_class != DirectClass)
    {
        dc_copy = rm_clone_image(image);
        (void) SyncImage(dc_copy);
        magick_free(dc_copy->colormap);
        dc_copy->colormap = NULL;
        dc_copy->storage_class = DirectClass;
        image = dc_copy;
    }

    GetExceptionInfo(&exception);
    histogram = GetImageHistogram(image, &colors, &exception);

    if (histogram == NULL)
    {
        if (dc_copy)
        {
            (void) DestroyImage(dc_copy);
        }
        rb_raise(rb_eNoMemError, "not enough memory to continue");
    }
    if (exception.severity != UndefinedException)
    {
        (void) RelinquishMagickMemory(histogram);
        rm_check_exception(&exception, dc_copy, DestroyOnError);
    }

    (void) DestroyExceptionInfo(&exception);

    hash = rb_hash_new();
    for (x = 0; x < colors; x++)
    {
        pixel = Pixel_from_PixelPacket(&histogram[x].pixel);
        (void) rb_hash_aset(hash, pixel, ULONG2NUM((unsigned long)histogram[x].count));
    }

    /*
        Christy evidently didn't agree with Bob's memory management.
    */
    (void) RelinquishMagickMemory(histogram);

    if (dc_copy)
    {
        // Do not trace destruction
        (void) DestroyImage(dc_copy);
    }

    return hash;
}