# Performing offline image conversion

You can convert the image characteristics of a file offline before transmitting a fax, or online while transmitting and receiving a fax. Because image conversion consumes significant processor time, you may want to perform file conversions offline to conserve CPU resources for processing events during an active fax session.

Use nfxConvertFileDirect to convert the image characteristics of a file offline. Specify the input file, the output file, and the desired image characteristics. Conversions of encoding type or page width do not affect image quality. Converting from a high resolution to a lower resolution will affect image quality. Converting an image from a lower to a higher resolution is not recommended, since the image cannot be improved and the resulting file is larger than the original.

NaturalFax supports TIFF-F files with different image formats on its pages by converting the format of all pages in the file to the format of the first page. If the file requires an image format other than that of the first page, use nfxConvertFileDirect to convert all the pages in a file to a specific image format. You can also use nfxSplitFile to split the original file into multiple files, each of which contains one or more pages that have the same image format. Splitting the file does not alter the image format of any of its pages. You may want to use nfxSplitFile to preserve the original image quality if a document has different resolutions on different pages.

Use nfxMergeFile to combine multiple pages stored in separate files into a single document for transmission. Merging the file does not alter the image format of any of its pages.

To verify that a document is in the correct format for transmission by NaturalFax, use nfxCheckTIFF.

File I/O intensive operations, such as TIFF-F or TIFF-S conversion or verification must not interfere with Natural Access event processing. Delays in application event processing can cause the fax session to time out. Applications must process events within three seconds of receipt. An application must continue processing events during an active fax session.

For more information, refer to Image format characteristics.