NXPowerLite's (and WeCompress's) file compression is a lossy one-way process so it is important to ensure that there is a record of how the file has been compressed. NXPowerLite and WeCompress insert a very small amount of metadata into each successfully compressed file which means next time any NXPowerLite product comes across it they can skip it safely. We call this metadata a 'Tag'.
Files will be shared with others and moved within file systems and inserting a Tag into the file means that it does not get lost. Adding a Tag does increase the size of the file very slightly but the total size of the Tag data is less than 100 bytes.
NXPowerLite (and WeCompress) uses any included Tag data to determine whether it can safely compress the file. As well as skipping compression entirely the Tag data can allow the software to make more informed decisions about how to compress the file. For example, it is possible for a file to be already compressed and then re-edited to add more content. In this case, the file will not be skipped and all the new content in the file will be considered for compression.
Currently PNG, TIFF and Zip files are not tagged.
What data is stored within a Tag?
If you use WeCompress.com you can expand the NXPowerLite Tag Data row from the results screen to view detailed information about the Tag. Below is an explanation about each:
Optimized: Shows if a file has been compressed by NXPowerLite/WeCompress or not - set to true for all files that have been compressed and left blank for any files that have not.
Version: This denotes the NXPowerLite product and version of the product that compressed the file. WeCompress uses the NXPowerLite SDK product to compress files.
Last Optimized Size: Size of the file in bytes when it was last compressed by NXPowerLite/WeCompress.
Allow JPEG: Specifies if NXPowerLite/WeCompress was set to allow conversion of other image formats to JPEG inside Microsoft Office and PDF files.
Allow Cropping: Images that have been cropped inside Microsoft Office files still retain the missing/cropped areas of the images. This setting specifies if NXPowerLite/WeCompress was set to delete these hidden portions of images.
Flatten: Specifies if embedded documents inside Microsoft Office files were flattened. Learn more about flattening embedded documents.
Allow Resizing: Specifies if NXPowerLite/WeCompress was set to allow large images to be scaled down inside Microsoft Office and PDF files.
Private Application Data: Specifies whether private application data & marked content has been removed from PDF files.
DPI: Specifies the resolution used to control how much images inside PDF, Word and Excel files are resized.
Target Width and Target Height: Specifies the resolution used to control how much images inside PowerPoint files are resized.
JPEG Quality: Specifies the JPEG quality used when converting, resizing or optimizing JPEG images - both standalone JPEG files and images inside Office and PDF files. Shown as a number between 1 (low quality/high compression) and 9 (high quality/low compression).