Rmagick histogram problems

I'm having problems accessing the hash returned by color_histogram(). There are only black and white pixels in my image, and this is very frustrating.

When I do

puts hist.inspect() # returns "{red=0, green=0, blue=0, opacity=0=>779753, red=65535, green=65535, blue=65535, opacity=开发者_运维知识库0=>6679}"

According to the documentation, the key is a Pixel object, so I construct

black = Magick::Pixel.from_color('black')
white = Magick::Pixel.from_color('white')

puts black.inspect # red=0, green=0, blue=0, opacity=0
puts white.inspect # red=65535, green=65535, blue=65535, opacity=0


puts hist[white] # raises exception: `[]': can't convert Magick::Pixel into Integer (TypeError)

Any ideas how I can access the histogram easily?

Thanks

You're changing hist somewhere between your color_histogram call and your hist[white]. This works for me with a simple black and white bw.png:

> i = Magick::Image.read('bw.png').first
=> bw.png PNG 100x100 100x100+0+0 DirectClass 8-bit 466b 
> h = i.color_histogram
=> {red=0, green=0, blue=0, opacity=0=>2342, red=65535, green=65535, blue=65535, opacity=0=>7658} 
> black = Magick::Pixel.from_color('black')
=> red=0, green=0, blue=0, opacity=0 
> h[black]
=> 2342 

And you "can't convert Magick::Pixel into Integer (TypeError)" error is easily reproduced using an Array:

> a = [ ]
=> [] 
> a[black]
TypeError: can't convert Magick::Pixel into Integer

A Hash will never produce that TypeError from a simple access.