Getting image dimensions with file_column

Rails
1

If I’m using file_column and RMagick to upload images and associate them
with my database records, what should I do to find out the exact
dimensions of a given image?

I can use the url_for_file_column command to link to them, but I’m not
sure how to find out the image’s height and width in my program.

Thanks!
Jeff

2

If I’m using file_column and RMagick to upload images and associate them
with my database records, what should I do to find out the exact
dimensions of a given image?

I can use the url_for_file_column command to link to them, but I’m not
sure how to find out the image’s height and width in my program.

I don’t remember where I got it, but this works for jpegs… used like:

jpeg = JPEG.new(“some.jpeg”)
puts jpeg.width
puts jpeg.height

class JPEG
attr_reader :width, :height, :bits

def initialize(file)
if file.kind_of? IO
examine(file)
else
File.open(file, ‘rb’) { |io| examine(io) }
end
end

private
def examine(io)
raise ‘malformed JPEG’ unless io.getc == 0xFF && io.getc == 0xD8 #
SOI

 class << io
   def readint; (readchar << 8) + readchar; end
   def readframe; read(readint - 2); end
   def readsof; [readint, readchar, readint, readint, readchar]; end
   def next
     c = readchar while c != 0xFF
     c = readchar while c == 0xFF
     c
   end
 end

 while marker = io.next
   case marker
   when 0xC0..0xC3, 0xC5..0xC7, 0xC9..0xCB, 0xCD..0xCF # SOF markers
     length, @bits, @height, @width, components = io.readsof
     raise 'malformed JPEG' unless length == 8 + components * 3
   when 0xD9, 0xDA:  break # EOI, SOS
   when 0xFE:        @comment = io.readframe # COM
   when 0xE1:        io.readframe # APP1, contains EXIF tag
   else              io.readframe # ignore frame
   end
 end

end
end

3

Thanks. I’m pretty certain RMagick actually has that stuff built into
it, I’m just not sure how to access it from inside my Rails application.

Jeff

Philip H. wrote:

I don’t remember where I got it, but this works for jpegs… used like:

jpeg = JPEG.new(“some.jpeg”)
puts jpeg.width
puts jpeg.height

4

Thanks. I’m pretty certain RMagick actually has that stuff built into
it, I’m just not sure how to access it from inside my Rails application.

Me too, but the less I can use imagemagick the happier I am :slight_smile: I was
really close to copying the source from php’s getimagesize function
which
can do gif, png, and bitmap as well, but found this which was enough for
me…

5

Yes, you can get it from RMagick, I believe its the image.cols and
image.rows to obtain the width and height.

If you want to avoid imageMagick, take a look at the commandline tool
jhead, which will give you that info easily.

http://www.sentex.net/~mwandel/jhead/

John.

Jeff C.man wrote:

Thanks. I’m pretty certain RMagick actually has that stuff built into
it, I’m just not sure how to access it from inside my Rails application.

Jeff

Philip H. wrote:

I don’t remember where I got it, but this works for jpegs… used like:

jpeg = JPEG.new(“some.jpeg”)
puts jpeg.width
puts jpeg.height

6

What I’m trying to do is get access to this information from within my
Rails program.

Assuming I have a model such as User, with an “image” field, what I’m
trying to do is get access to dimensions of the User’s image.

I know how to do url_for_file_column(‘user’, ‘image’), but how would I
get access to the dimensions, how would I create the RMagick/ImageMagick
object to call on the “cols” and “rows” methods?

I’m surprised this doesn’t seem to have come up for any others, or
perhaps I’m just missing something. I don’t think a command-line tool
is quite what I’m looking for, because I want my controller and view to
have access to these numbers.

Assuming that I have a User object with an “image” field created by the
file_column plugin, does anyone know exactly how I could access the
RMagick object for that image?

Jeff

Guest wrote:

Yes, you can get it from RMagick, I believe its the image.cols and
image.rows to obtain the width and height.

If you want to avoid imageMagick, take a look at the commandline tool
jhead, which will give you that info easily.

7

This is not a very helpful answer to your problem, but I looked at
file_column and acts_as_attachment. I found the latter to be nicer for
working with images. I am able to access image geometry with
acts_as_attachment.

8

Guest wrote:

Yes, you can get it from RMagick, I believe its the image.cols and
image.rows to obtain the width and height.

It is actually image.columns and image.rows