RMagick - ImageMagick gives error "no decode delegate for this image format"

Question

The problem occurs when i try to manipulate an image uploaded from sinatra.

File.open(params[:file][:tempfile]) do |p|
   thumb = Magick::Image.read(p)
   thumb.crop_resized!(75, 75, Magick::NorthGravity)
end

The uploaded file is a jpeg, form data when uploading image includes

{:filename=>"299732_176749115737355_100002068035867_380115_618512842_n.jpg",    :type=>"image/jpeg", :name=>"file", :tempfile=>#<File:/var/folders/hf/d6vx6vg56nbd5n44jjrp84k80000gn/T/RackMultipart20120228-55947-1fd2l6c>, :head=>"Content-Disposition: form-data; name=\"file\"; filename=\"299732_176749115737355_100002068035867_380115_618512842_n.jpg\"\r\nContent-Type: image/jpeg\r\n"}

And also ImageMagick has the necessary delegates

convert -list configure

returns

DELEGATES     bzlib freetype jpeg jng jp2 lcms png tiff x11 xml zlib

So, i should be able to upload and transform a jpeg, but it whines about delegates. Also i am working on Mac OSX 10.7, maybe another weird problem with mac

Answer 1

I found solution for me:

tmpfile = params[:file][:tempfile]
image = Magick::ImageList.new
bin = File.open(tmpfile, 'r'){ |file| file.read }
img = image.from_blob(bin)

I suppose problem occurs because rmagick try to define image type by file extension. But uploaded file without extension. Good luck!