RMagick - how do I find out the pixel dimension of an image

问题

This may be a stupid question, but how does one find the image width and height in pixels?

image.x_resolution and image.y_resolution both return 0 for some reason.

回答1:

require 'rmagick'
img = Magick::Image.ping( 'demo.png' ).first
width = img.columns
height = img.rows

Note .ping method imported from comments. If you need to read the image to process it, then use Magick::Image.read( 'demo.png' ).first - the use of ping works in this stand-alone code and speeds processing up for some image types where IM can just read a header block. This is useful for cases where you don't need to load the image itself to do work on it.

回答2:

You can get the image dimensions from img.inspect - instructions included at http://www.imagemagick.org/RMagick/doc/image2.html

An example would be

 f.inspect » "images/Flower_Hat.jpg JPEG 200x250 DirectClass 8-bit 9kb"

来源：https://stackoverflow.com/questions/16266933/rmagick-how-do-i-find-out-the-pixel-dimension-of-an-image