IMPAX can store two formats of images: JPEG and wavelet. The two formats make use of both the lossless and lossy compression methods. (Also refer to Choosing image quality.)
JPEG images
The JPEG image is typically the image as it was produced at the modality (this is also known as the original image). Though often having lossless compression, the JPEG image may have lossy compression applied by the modality or through IMPAX Server configuration. JPEG images are not displayed in the Image area until all images data for the displayed images is displayed. As images can be large and networks slow, a noticeable delay may occur when loading JPEG images on slower networks or when accessing IMPAX remotely.
Wavelet images
Wavelet images are a copy of the original image with added wavelet encoding. This encoding optimizes the display of images on monitors of various resolutions. Wavelet images are displayed progressively, meaning that some data is retrieved and displayed immediately, then more and more is added as the image fully loads. This often results in faster image display. However, images with greater bit depth (such as NM images, most MR images, and about half of all CT images) must be lossy compressed to support the wavelet encoding.
Deciding on image format
When deciding which image format to view, consider the following factors:
| JPEG | Wavelet | |
|---|---|---|
| DICOM standard | X | |
| Agfa proprietary format | X | |
| Supports lossless compression | X | X |
| Supports lossy compression | X | X |
| Progressive loading when displaying images | X | |
| Ability to print image from IMPAX | X | |
| Ability to export image (such as burn to CD or DVD) from IMPAX | X | |
| Ability to view image using an application other than IMPAX | X |
IMPAX configuration
To use wavelet images, a Curator must be installed and configured as part of the IMPAX cluster. If not using a Curator at your site, you must configure all IMPAX Clients to retrieve original images only. (This is the default setting.)
For detailed Curator information, refer to the Curator and CD Export Server Installation Guide and the Curator component of the IMPAX 6.5.1 Server Knowledge Base.
Intended use of image
JPEG images, which are the DICOM standard, are required for exporting images to be used in presentations reports, and so on, transmitting images to other application, and printing of images to film.
Network and display speed
On a dedicated and optimized 100baseT+ network, the JPEG image may actually load more quickly than the wavelet version. On lower bandwidth networks, however, or when accessing IMPAX remotely, the wavelet image is faster.
Furthermore, only wavelet images load progressively and become sharper and sharper as more data is retrieved. JPEG images, by comparison, do not appear until fully loaded. Therefore, on slower networks, previews of wavelet images can typically be seen sooner than JPEG images even if the time to fully load them is the same as the JPEG images.
Wavelet image display speeds can be further accelerated by optimizing wavelet images for performance. Such optimizations are not possible with JPEG images.
Monitor resolution
Wavelet images scale to monitor size, optimizing data display for the available number of on-screen pixels. This makes them more suitable to viewing on a variety of monitor sizes, including low-resolution monitors. On large, high-resolution diagnostic monitors, however, the wavelet images may load so much data that they become virtually identical to the JPEG images.
 | Tip: Wavelet compression options are set in the IMPAX 6.5.1 Administration Tools. Refer to “Compressing images sent to stations” (topic number 9535) and “Web Compression Manager” (topic number 9541) in the Administration Tools component of the IMPAX 6.5.1 Server Knowledge Base. |