Get Image Resolution: Source Code

This movie script will attempt to determine the format and resolution of a graphic file, by directly reading the header.

General notes:

1. This is a Movie script. This is NOT a behaviour, NOT a parent script.
2. The code will work in Macromedia Director 7.0 or later.
3. The code requires the BinaryIO Xtra by Glenn Picher, available at http://www.updatestage.com/xtras/binaryio.html.

Copy and paste the source code below into a movie script.

-- Determine Graphic File Resolution

-- Copyright (c) 2001 Kendall Anderson. All rights reserved.
-- http://invisiblethreads.com


-----------
-- OVERVIEW
-----------
-- Code to read the width/height of a specified graphic file
-- Currently only identifies .BMP, .GIF, .TGA because these formats
-- can be parsed in a very similar way (easily identifiable header,
-- seek to specific location and read data).

-- Note that the .TGA recognition is a little dodgy, so it is tested
-- last, after other formats. (it depends on matching a single number only)

-- Other formats (.JPG, .TIF) require a (little) bit more parsing
-- and could be easily incorporated. This code is meant to serve as
-- an example of the process.

-- Details about file formats found at: http://www.wotsit.org


---------------
-- CODE HISTORY
---------------
-- Nov 17 2001: Kendall Anderson: Initial design and coding

------------------------------------------------------------------------------------
------------------------------------------------------------------------------------


-- given a filename, try to determine the type of graphic file
-- and if successful return the image resolution as a property list
-- [ #width: integer width, #height: integer height ]

on _GetResolution dFilename
  
  --register(xtra "binaryio","your serial num here") -- this should only be done once, elsewhere!
  
  oFile = new(xtra "binaryio")
  dErr = openfile(oFile, 1, dFilename)
  
  sType = _DetermineFileType(oFile)
  
  if (sType = 0) then
    put "Unidentified file format"

    lRes = [ #width: 0, #height: 0 ]
  else
    lRes = _GetFileResolution(oFile, sType)
    put "File type: " & sType
    put "Image resolution: w: " & lRes.width & ", h: " & lRes.height
  end if
  
  oFile = void
  
  return lRes
  
end



-- given a file pointer reference, try to determine what kind
-- of file this is by reading the header information

on _DetermineFileType oFile
  
  -- lHeader format:
  -- start location of header, # chars to read, text(s) to match
  lHeaders = [:]
  lHeaders.addProp(#bmp, [ 0, 2, [ "BM", "BA", "CI", "CP", "IC", "PT" ] ])
  lHeaders.addProp(#gif, [ 0, 3, [ "GIF" ] ])
  lHeaders.addProp(#tga, [ 2, 1, [ numtochar(1), numtochar(2), numtochar(9), numtochar(10) ]])
  
  sType = 0
  repeat with i = 1 to lHeaders.count         -- check each type until we get a match
    bFound = _CheckHeader(oFile, lHeaders[i])
    if (bFound) then
      sType = lHeaders.getPropAt(i)
      exit repeat
    end if
  end repeat
  
  return sType
  
end



-- given a file pointer reference and the type of the file,
-- read the image resolution (location of data dependent on file type)

on _GetFileResolution oFile, sType
  
  -- configure location of width value, and length of data for different file types
  
  -- lDetails format:
  -- start location of width data, # of bytes for data
  -- assumes height data occurs immediately after width, in same format
  lDetails = [:]
  lDetails.addProp(#bmp, [ 18, #long ])
  lDetails.addProp(#gif, [ 6, #short ])
  lDetails.addProp(#tga, [ 12, #short ])
  
  return (_ReadResolution(oFile, lDetails[sType]))
  
end


-- given file pointer, try to read header data to verify file type

on _CheckHeader oFile, lData
  
  bMatch = FALSE
  
  dOffset = lData[1]   -- offset where we check for match
  dLength = lData[2]   -- # of bytes to read
  lValid = lData[3]    -- list of valid matching strings
  
  -- check id header
  setFilePosition(oFile, dOffset)
  sID = readBytes(oFile, dLength)
  
  repeat with dItem in lValid   -- check for valid matches
    if (sID = dItem) then       -- if valid match
      bMatch = TRUE
      exit repeat               -- exit loop
    end if
  end repeat  
  
  return bMatch  
  
end


-- given file pointer and data describing location of resolution data,
-- read resolution data and return as proplist

on _ReadResolution oFile, lData
  
  dOffset = lData[1]  -- offset where we find data
  sType = lData[2]    -- data type: #short (2 bytes) or #long (4 bytes)
  
  setFilePosition(oFile, dOffset)
  
  case (sType) of
    #short: sMethod = #readUnsignedShort  -- handler within BinaryIO
    #long:  sMethod = #readUnsignedLong   -- handler within BinaryIO
  end case
  
  dWidth = call(sMethod, oFile)
  dHeight = call(sMethod, oFile)
  
  return [ #width: dWidth, #height: dHeight ]
  
end