Xerox DocuMate 4830 User Manual page 159

Compression Options
There are two types of image compression functions used during scanning. The input compression option is
compressing the image when transferring it from the scanner to the TWAIN driver on the computer. The output
compression option is the TWAIN driver compressing the image before it sends the image to the scanning
application. In the scanning interface the input compression option is Compress transfers and the output option is
Compression.
Compress transfers
Select this option to have the scanner compress the image in Gray and Color scans. This reduces the file size and
allows for faster image transfer from the scanner to the computer. Once the compressed image is on the computer,
scanner's driver will then uncompresses the image, and perform any image processing functions that have been
selected in the scanning interface. The uncompressed image is then transferred to the scanning application. With
Compress transfers, a scanning application such as Nuance PDF Converter, will receive the uncompressed image and
save the image in whatever file format it uses. You can use the Quality slider to adjust the level of compression you
want to use.
When the Quality option is set to High quality, there is very little visual difference between a compressed scan and
an uncompressed scan. When the quality option is set to High compression, there may be a greater visual difference
between compressed and uncompressed scans.
Quality
You can fine tune the compression level by adjusting the quality slider between high compression and high quality.
When the quality level is set to high compression, the scanner will scan and transfer images faster than high quality,
but the image quality of the output scan will be lower.
Subsampling
The subsampling options allow you to select the encoding ratio between color information and luminosity.
Subsampling works by lowering the resolution of the RGB colors found in an image without affecting luminescence
of the image. This compresses the image to create smaller file sizes but it can sometimes result in loss of image
quality. Depending on the type of image being scanned, subsampling encoding may not have a noticeable affect in
the final image file. You should try test scans using the different levels of subsampling to make sure you are happy
with the image quality.
• 4:4:4—no subsampling and the ratio between color and luminosity remains unchanged.
• 4:2:2—mid-level ratio between color and luminosity.
• 4:1:1—highest ratio difference between color and luminosity, which results in saving the smallest file size.
Compression
This option is specific compression for file and memory transfers to an application. It is only available if the
application you are using can accept a compressed image file. For instance, if your scanning application is set to
receive JPEG compressed images, then the Compression field will display JPEG. Otherwise, the status for
Compression will always be disabled and display Uncompressed because the scanning application you are using is
requesting an uncompressed image.
The Compress transfers option described herein compresses the image for faster transfer from the scanner to the
computer. The driver uncompresses the image and transfers the uncompressed image to the scanning application.
The Compression option will often be disabled as most applications do not support receiving a compressed image
file from the scanner driver.
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Xerox DocuMate 4830
User's Guide
159