Perl Graphics Programming

Retrieving and Setting File Information

You can retrieve a lot of general information about an image by using the Get( ) method to query any of the attributes in Table 3-2. A few of the attributes (compression, interlace, filename, etc.) may also be written to with the Set( ) method. Setting these attributes does not immediately affect the image; they do not come into play until the image is written. Ping( ) is a handy function that returns information about an image’s size without actually loading the image into memory.

Most of the attributes listed below can be both read and written; those with a “No” in the Write column are read-only (that is, they may be used only with the Get( ) method, not with the Set( ) method). For the methods, you can use the name of the method with the word “Image” appended to it as an alias. For example, ReadImage( ) is an alias for Read( ) and SharpenImage( ) is an alias for Sharpen( ).

Table 3-2. File information attributes

Attribute	Read	Write	Description
adjoin	Yes	Yes	Certain file formats accept multiple images within a single file. If adjoin is 1 and the image is a multi-image format, multiple reads to the same image object join the images into a single file. Set adjoin to 0 if you do not want the images output to a single file.
Base_filename	Yes	No	Returns a string that is the image’s original filename.
cache-threshold	Yes	Yes	ImageMagick keeps the image data in a RAM cache and writes it out to a disk cache when it runs out of RAM. If you have a limited amount ...