Demand Loading is the ability to load and display extremely large raster documents (up to 4 GB in size) using a relatively small amount of memory (generally under 40 MB). Demand Loading is especially useful with operations such as scan-to-file.
With Demand Loading, documents can be displayed progressively, while they are being loaded. If files are not locked, they can be opened while they are still being written. The progressive loading can be cancelled at any time; the portion of the document that did load can still be viewed (i.e. scrolled or zoomed). With very large files, this allows quick loading of a specific portion of the document.
A preview image can be created and loaded to provide a rapid view of the document. Previews can also be used for some scrolling and zooming of the document to prevent wait times during loading.
Demand loading applies to the following formats:
• TIFF – Raw
• TIFF – Group3
• TIFF – Group4
• TIFF - PackBits
• TIFF - LZW
• BMP – Raw
• JPEG
• PNG – Flate
• PDF – Raw raster component only
• PDF – Flate raster component only
• PDF – LZW
To use Demand Loading:
Enable the
"Minimize Resources" option in the Optimize category (Preference
> Options, 
System, Optimize). If the file is larger
than 1MB, Demand Loading will then be used.
Demand Loading is used automatically
when the file is larger than the value defined in the Demand
Loading File Size setting. The default value is 10 MB
Enable the
"Use Previews" option in the Optimize category (Preference >
Options, System, Optimize) to turn on creation and loading
of preview images.
If they exist, previews are automatically
loaded. If no preview exists for a 24-bit color raster, one is created
in memory and loaded. Previews can also be used for viewing actions, such
as zooming or viewing the document in the Reference window. Previews can
be saved with some file formats, for example, TIFF.
You may also change the Maximum Preview Image Size and Preview Image Size Factor values, if required. Maximum Preview Image Size defines the maximum allowable size for previews while Preview Image Size Factor determines the size of a preview image for large raster files.
To enable the progressive view-while-loading feature:
Enable the
Enable View While
Loading setting so that loading and viewing occur simultaneously;
the file is displayed while it is being read from disk so you can see
on the screen how the load is progressing.
If a document will take less than
2 seconds to fully display, view-while-loading will not be used. Additionally,
only the raster image types specified above and non-rotated images can
be displayed in this manner.
Enabling Fast Scrolling is recommended when loading these large files, but is not required. With Fast Scrolling enabled, a full refresh of the display is not required when panning or scrolling, only new portions of the image are repainted.
To enable Fast Scrolling:
Enable the "Fast Scroll" option in the
Optimize category (Preference > Options, System, Optimize).
See also