From: Mike Meng <meng.yan@...>
Date: 2006-09-17T00:46:05+09:00
Subject: RMagick problem: Image::read works well but Image::from_blob fails

Hi all,
    I want to determine the geometry of an image. The image file may be
in local harddisk or on web. So I use open-uri and
Magick::Image::from_blob to do that work, here is the code:

open('<path or URI of image file>') { |f|
    image = Magick::Image::from_blob(f.read).first
    puts "Width: #{image.columns}; Height: #{image.rows}"
}

For most of the cases, this works well. However, we I tried to read an
JPEG generated by my Ricoh Caplio digital camera, it failed and emitted
these message:

---------- code ----------
E:/workspace/ruby/idapted/testrmg.rb:6:in `from_blob': JPEG datastream
contains
no image `' (Magick::ImageMagickError)
  ....
-----------------------------

  Surprisingly enough, if I use Magick::Image::read method to read the
same image file directly from harddisk, everything is fine, here is the
code:
---------- code ----------
g = Magick::Image::read('<local file only>').first
puts "Width: #{g.columns}; Height: #{g.rows}"
-----------------------------

  Why do Image::read and Image::from_blob make differeces? How to
determine the geometry of  a remote image?

  Any comment is appreciated. Thanks!