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Detailed information is provided on the test procedures used. The comparison examines technology,compression cost, functionality and speed, image quality, usability, installed user bases, and developmentSoftware Development (SDK) toolkit available for both products, broken into the following sections:

Test procedures - Procedures used to compare ECW and MrSID

Compression - Prices, functionality, speed, size of compressed images

Quality - Compressed image quality

Usability - Viewing speed, ease of use, product compatibility, installed user base, Internet usageand SDK availability

Technology - Concepts and technology behind ECW v2.0 and MrSID

To ensure an open, fair and reproducible comparison, full details about the hardware, software,configurations, images, and test methods used are detailed. Side-by-side image comparisons are alsoincluded. You can duplicate the comparison by performing the comparison yourself with the freeER Mapper evaluation CD-ROM. The images used in this comparison are available on CD-ROM in TIFF,MrSID and ECW format.

All brands, company names and product names are trademarks or registered trademarks and theproperty of their respective owners.

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Test proceduresSide by side comparisons were performed as follows:

Software tested:

• ER Mapper 6.0 with the ECW v2.0 Compression Enhancement Pack.

• MrSID Publisher 1.3

Hardware:

• Windows NT 4 SP 4, Pentium III 400Mhz, 256MB RAM

Software used to evaluate compression results:

The compressed ECW and MrSID images were tested in a range of products, including ArcView, MapInfoand Photoshop. Analysis of image quality was examined at a variety of resolutions. Geospatial accuracy,color quality and sharpness were evaluated, as well as the speed to view and decompress images.

Images:

Four test images were selected, ranging in size from 1GB down to 13MB for the input images. One of thetests included multiple input images to be mosaiced out to a single compressed mosaic.

GB_COLOR.TIF(1GB)

DOQQ mosaic images(344MB)

GRAYSCALE.TIF(64MB)

PHOTO.TIF(13MB)

Uncompressed overview and detail for the four uncompressed test images

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Parameters used for compressionThe following table summarizes the input images and test results (full test results are provided infollowing sections) and compression parameters used, as recommended by the manufacturers.

GB_AIRCOLOR 8 x DOQQ GRAYSCALE PHOTODescription 1GB Color

airphoto8 x USGS

DOQQ'sGrayscale

orthophotosScanned color

35mm

D e s c r i p t i o n

Grayscale

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Compression

Pricing and functionalityBefore compressing imagery, a range of image processing is required to prepare images for compressionand distribution. For example, when compressing mosaics of images, a typical workflow is to:

• Orthorectify or geocode the source images.

• For orthorectification, grid the DEM from X,Y,Z point data.

• Mosaic and color balance the source images

• Combine multi-resolution imagery

• Perform image processing functions.

• Add vector data

The following table compares the ER Mapper 6.0 functionality (which includes the ECW v2.0Compression Wizard as one of the integrated mapping functions performed by ER Mapper) with theMrSID Publisher product (which has image compression and limited mosaicing ability).

Both ECW and MrSID offer two products for compression, one to compress images larger than 500MB(ER Mapper 6.0 and MrSID Publisher), and one to compress images smaller than 500MB (ECW FreeCompressor and MrSID Professional).

The inability of MrSID to integrate image compression with other image processing operations was foundto be a substantial limitation.

Comparison of product pricing and level of support provided

Pricing ER Mapper 6.0 withECW v2.0

MrSID

Product to compress less than 500MBimages

Free(ECW FreeCompressor)

$1,500(MrSID Professional)

Product to compress any size images $4,930(ER Mapper 6.0)

$5,000(MrSID Publisher)

Price includes 12 months support andupdates

Yes No

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Comparison of image preparation functionality

Image preparation ER Mapper 6.0with ECW v2.0

MrSID

Orthophoto rectification Yes No

Feathered mosaics Yes No

Color balancing Yes No

Surface gridding Yes No

Vector rasterization engine Yes No

Inregion polygon clipping Yes No

Multi-surface fusion Yes No

Image processing functions Yes No

Comparison of compression functionality

Compression functionality ER Mapper 6.0 with ECWv2.0

MrSID 1.3

Image formats directly read ALG, ERS, ECW, TIFF,GeoTIFF, JPG, DOQQ,LAN, ARC/INFO .HDR,Spot View. Many vectorformats

TIFF, GeoTIFF, LAN,ARC/INFO HDR, SunRaster. No vector formats

Import of other image formats More than 100 None

User can add new input formats Yes No

Multi-CPU support Yes No

Multi-resolution input images Yes No

GUI and Command Line interface Yes Yes

Batch Compression Yes Yes

Preview mosaics prior tocompression

Yes No

Mosaicing Yes Limited

Seamless mosaics Yes No

Color balanced mosaics Yes No

Maximum allowed input image size > 1TB (1,000GB) > 100GB

Maximum allowed compressedimage size

unlimited 2GB

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Compression speed to compress and compression throughputThe two charts show compression speed for ECW v2.0 and MrSID.

In all comparisons, ECW v2.0 compression is significantly faster than MrSID.

This is an important consideration when compressing large amounts of imagery. For example,compression of 100GB of imagery will take about 1 day with ECW v2.0 where as MrSID would take over3 days to compress the same amount of imagery.

As MrSID does not take advantage of multi-CPU machines, this compression comparison was performedon a single-CPU machine. On a dual CPU machine, testing of the ECW compressor showed it to be evenfaster, with a further 40% and 95% increase in speed.

1GB

_CO

LOR

8 x

DO

QQ

GR

AY

SC

ALE

PH

OT

O

0

500

1000

1500

2000

2500

Sec

on

ds

1GB

_CO

LOR

8 x

DO

QQ

GR

AY

SC

ALE

PH

OT

OCompression Time in Seconds

(smaller is better)

ECW v2.0

MrSID 1.3

1GB

_CO

LOR

8 x

DO

QQ

GR

AY

SC

ALE

PH

OT

O0.00

0.20

0.40

0.60

0.80

1.00

1.20M

B/s

eco

nd

1GB

_CO

LOR

8 x

DO

QQ

GR

AY

SC

ALE

PH

OT

O

Compression speed in MB/second (larger is better)

ECW v2.0

MrSID 1.3

Chart 1: Compression Time in Seconds and Throughput in MB/second

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Size of compressed imagesBoth ECW v2.0 and MrSID generate compressed imagery by specifying a target compression ratio. Thisratio dictates the quality of the final image.

In all cases, ECW v2.0 produced smaller compressed images than MrSID for a given image quality(compression ratio). This is most likely because the ECW technology uses multiple encoding(compression) techniques, and selects the best for each area in the image.

Compressed image quality is as least as important as compressed image size. As detailed in the Qualitysection, the ECW v2.0 compressor consistently produced better quality results than the MrSIDcompressor, and did so in a faster time while producing smaller compressed images.

1GB_COLOR 8 x DOQQ GRAYSCALE PHOTO0

5

10

15

20

25

MB

1GB_COLOR 8 x DOQQ GRAYSCALE PHOTO

Compressed image size in MB (smaller is better)ECW v2.0

MrSID 1.3

Chart 2: Size of compressed images in MB

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QualityImage quality was compared using several measurements. Each image was roamed and zoomed intodifferent areas and type of image information to compare these quality measurements:

• Analysis of images at an overview perspective

• Analysis at a detailed level

• Analysis of feature edges and definition

• Geometric and pixel accuracy

• Analysis of color contrast, balance and image detail

In all cases, the ECW images were better quality or of comparable quality to the MrSID images. Therewere no cases found where the MrSID image quality was better than the ECW image quality.

Quality of the color 1GB airphoto imageECW achieved a compression rate of 83:1 resulting in a 13MB file. MrSID achieved a much lowercompression rate of 45:1 resulting in a 23MB file.

The following table shows an overview of the uncompressed, ECW and MrSID images. As can be seen,the MrSID was very blurry, and continued to be blurry until zoomed into a detail level.

Both ECW and MrSID images showed good color balance, no significant edge loss, and good balance andimage detail, and the results were judged as very acceptable, other than the blurry overviews with theMrSID images. ECW retained a slightly high geometric accuracy and color balance.

Uncompressed ECW Compressed MrSID Compressed

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Image quality comparison for 1GB color airphoto

It is worth highlighting that for a target compression ratio of 40:1, the ECW compressor achieved anactual compression rate of 85:1 and the MrSID compressor achieved 45:1 for this image, so despitebeing of equal quality, the ECW image is much smaller (13MB for the ECW image compared to 24MBfor the MrSID image).

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Quality of the grayscale 344MB DOQQ mosaic (20:1 compression)Both ECW and MrSID produced compressed images of good quality, even at a compression ration of20:1, which is fairly high for grayscale imagery. Again, the MrSID image was slightly blurrier than theuncompressed or ECW image.

Uncompressed ECW Compressed MrSID Compressed

Image quality comparison for 334MB DOQQ orthophoto mosaic

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Quality of the grayscale 64MB orthophoto mosaic (20:1 compression)Overall, both provided excellent compression. The MrSID image was slightly blurry at all levels, and hadslight edge jitter at detailed zoom level (here shown over a freeway section).

Uncompressed image ECW image MrSID image

Image quality comparison for 64MB high resolution airphoto mosaic

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Quality of the color 13MB scanned 35mm photograph (20:1 compression)The scanned 35mm photo had almost identical results for both ECW and MrSID, except that again theMrSID image was slightly blurry at top-level zooms.

Uncompressed image ECW image MrSID image

Image quality comparison for Kodak Photo CD scanned 35mm photo

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ObservationsDuring quality comparisons, the ECW format displayed noticeably faster, in all applications tested. Forlarger images, the speed difference was very significant - in some cases the ECW images displayed 10times faster than the MrSID. In all cases, the ECW images displayed at least twice as quickly as theMrSID images.

Some additional tests were performed at higher compression 50:1 compression ratios. The ECW formatperformed much better at higher compression ratios than the MrSID format, with much less blurring andless loss of features and definition, although this may not be that important, as the ideal compressionratios seemed to be in the 10:1 to 20:1 range for grayscale images, and 20:1 to 40:1 for color images toproduce results that still had high definition, color balance, and clarity.

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Usability

Installed user baseEarth Resource Mapping has developed and marketed the ER Mapper product for 10 years, with regionaloffices in San Diego, USA covering the Americas region, in London, UK for Europe/Africa/Middle East,and in Perth, Australia for the Asia Pacific region, as well as many country level offices. The ECWcompression engine is included in all copies of ER Mapper 6.0. ER Mapper has a significant installeduser base, is installed in over 120 countries and is supported by a world wide network of over 500resellers.

LizardTech, Inc. is a smaller company with an office in Seattle, USA. With a more limited reseller andsupport network, and being a younger company than Earth Resource Mapping, there is a smaller installeduser base using the MrSID compression technology.

Product supportIt is difficult to establish an exact comparison of products that support the ECW format and the MrSIDformat. Many of the products listed as being supported by MrSID are either beta versions of pluginsoffering limited functionality, or the products themselves were not released at the time that thiscomparison was performed.

Both products support the major GIS products, and both offer stand alone viewers, ActiveX / ATLcomponents, and web browser support.

The ECW viewer (ER Viewer) is a freely available viewer than can be shipped with any imagerycompressed with ECW format, at no charge. The MrSID viewer is also free for download, however datasuppliers wishing to supply the viewer with compressed images must pay a royalty fee.

The ECW decompression libraries enable any application to use imagery via the Internet; the MrSIDproduct only supports web browsers to access remote imagery.

Both products support web AutoCAD Map, ArcView, MapInfo, MapX, MS Office, Photoshop and webbrowsers. ECW has all common application interfaces: OLE, ActiveX and ATL. MrSID offers an ActiveXinterface only. Currently there would appear to be slightly more released products that support theMrSID format in a final non-beta form than the ECW format. Four software companies contacted duringthis review indicated they would be supporting ECW in favor of MrSID because ECW offers bothcompression and decompression SDKs, indicating the situation is evolving rapidly.

MrSID only provides decompression/viewing SDK’s for applications. This means that all imagery must becompressed using one of the LizardTech MrSID compression products. The MrSID library only enablesaccess to local compressed images - applications can not access to imagery served via the Internet usingthe MrSID decompression SDK library.

Many software companies are justifiably nervous about depending on an external 3rd party product forimage compression. Given that the version 2.0 of ECW recently released by Earth Resource Mapping alsoincludes a free compression SDK, and given the announcements already made by companies adding ECWsupport to their products, the number of products supporting the ECW format is expected to increaserapidly.

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Internet usageCompressed images open up the ability to be able to serve images via the Internet (or intranets) to users.Both ECW and MrSID support the ability to serve images via the Internet or intranets.

Comparing image server technology is beyond the scope of this comparison document, however somesimple tests were performed, including time to view images, and usability of access via the Internet.

ECW v2.0 supports access of remotely served images from within web browsers and within applicationsoftware such as GIS products. The MrSID products only offer web browser based access of remotelyserved images.

The remote access of a 60GB mosaic served with ECW’s Image Web Server was compared with theremote access of a 2.6GB mosaic served with MrSID’s Image Server (this was the largest MrSID imagethat could be found for the comparison - note that the ECW image being served is over 20 times largerthan the MrSID image). Both image servers were remotely located on the Internet.

The comparison involved selecting 4 features within each of the images, and measuring the time taken tozoom and roam to show each of those features.

Feature comparison ECW v2.0 MrSID 1.3

Time to roam and pan to 4 features via an internet server 12 seconds 108 seconds

Real time roaming and panning Yes No

Progressive Image update Yes No

The ECW Image Web Server performed significantly better than the MrSID Image Server in everyrespect. The lack of progressive image update, and the lack of real time roaming and zooming, wereparticularly limiting in the MrSID Image Server.

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Comparison of image access via the InternetThe following images demonstrate the difference between the two systems. The images were accessedfrom within Internet Explorer 5. Note the progressive image update occurring on the ECW image, andnote that the MrSID image does not update in real time, and leaves phantom image copies behind whileroaming, making it very difficult to use.

ECW Image Web Server MrSID Image Server

ECW image via the Internet after quickly roaming.Note the progressive image update underway in thebottom-right corner (the blurry part of the image).

MrSID image via the Internet after quickly roaming.Note the garbage phantom images while roaming.

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Software development kits (SDK) and developer support

Feature ER Mapper ECW v2.0 MrSID 1.3

Decompression SDK and cost Yes, free, unrestricted Yes, free, restricted license

Compression SDK and cost Yes, free, unrestricted No

Access internet based images Yes No

Decompression performance:sequential decompression

22 seconds 82 seconds

Decompression performance:Multiple view roaming/zooming

12 seconds 108 seconds

Supports progressive image update: Yes No

ECW and MrSID both have decompression libraries to enable applications to add support for readingcompressed imagery.

ECW compression and decompression libraries to enable application developers to both read and createcompressed image files. This is a significant difference between the ECW and MrSID marketphilosophies.

The MrSID format is a closed format - only the MrSID products can create compressed image files.

There are several differences between the level of support provided to application developers:

• The ECW SDK include libraries for both decompression (viewing) and compression. This makes theECW format much more open than the MrSID SDK, which are only provided for decompression(viewing) - images must always be compressed with the MrSID products. This locks applications intousing a 3rd party product, which is not desirable. Note, however, that the free ECW compression SDKsupports a maximum input images to 500MB - the full ER Mapper 6.0 product must be purchased tocompress images larger than 500MB in size.

• The ECW compression and decompression/viewing SDKs can be used by anyone can add imagecompression and decompression/viewing (even competitors to the ER Mapper product). On the otherhand, the MrSID decompression libraries are restricted by LizardTech, and by their licensingagreements with the US Government on the technology. LizardTech will not license thedecompression to companies seen as competitors, which limits its appeal as a generic format.

• The ECW SDK provides automatic support for accessing imagery via the Internet within applications;the MrSID library only provides support for reading local files.

• The ECW decompression/viewing SDK provides much faster decompression and viewing of imagerythan the MrSID SDK. Tests performed during this comparison show that applications using the ECWSDK to view compressed imagery display or print imagery between 300% and 900% faster thanapplications using the MrSID SDK to decompress and view imagery. Given that a the final goal forcompressed imagery is to enable quick access, this is a significant feature of the ECW SDK over theMrSID SDK.

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TechnologyBoth products compress by transforming images into wavelet space using Discrete WaveletTransformations (DWT) and then quantizing and encoding the wavelet space images. Quantization reducesinformation content, so that the encoding phase can compress the imagery.

The DWT process is a 2D filtering process. This has historically meant that large images could not becompressed, as the computer would require as much RAM as the size of the image being compressed,making it impractical to compress GB or TB images.

The ECW v2.0 and the MrSID compression technology both eliminate the need for large amounts ofRAM during compression, thus enabling very large images to be compressed.

The crux of compressing large images is how the DWT is performed for large images. Both products usedifferent techniques, which have important implications for the performance and capabilities of theproducts.

ECW technology

The ECW compression engine uses discrete wavelet transformation (DWT) technology developed by Mr.Stuart W. Nixon, Founder and CEO of Earth Resource Mapping. Mr. Nixon is also the inventor for thedynamic algorithm compiler technology used by ER Mapper, which has been the basis for ER Mapper’ssuccess in the desk top image process market.

The ECW DWT is based on a fundamental wavelet mathematics breakthrough by Mr. Nixon, and is U.S.Patent Pending. The multi-level DWT is computed recursively and generated on a line by line basis,directly from the original imagery, which is read on a line by line basis. Because of the recursive DWTgeneration (which is the crux of the ECW invention), the ECW DWT can process images of any size,without needing to resort to tiling or disk caching of intermediate DWT operations.

Thus, an entire multi-level DWT or iDWT operation can be performed on very large images, with a verylow memory “footprint” during the process. This is a critical requirement for compressing large images.For example, the ECW DWT technology can perform a full and complete DWT operation on a 1,000,000x 1,000,000 pixel image (e.g. 1TB or 1,000GB) with only 128MB of RAM required during the DWTprocess (additional RAM is required for the follow on quantization and encoding stages used to compressimages, which are not directly related to the DWT process).

A critical difference between the DWT process used by EWC and MrSID is that the ECW process doesnot have to break an image in to “tiles” before performing the DWT process, and the ECW process doesnot have to store intermediate tile results on disk during the compression process.

As the DWT invention by Mr. Nixon is a fundamental wavelet breakthrough, it has applicability to a widerange of applications not related to compression. For example, Mr. Nixon’s DWT invention can be usedto fuse images of different spatial resolution, by performing the DWT on the two images, adding thewavelet information together, and then performing the inverse DWT. The entire process performs in apipelined fashion, with no intermediate disk files required. Other DWT applications for the inventioninclude image enhancement and feature recognition. As these are beyond the scope of this comparisondocument, they will not be detailed here. Further information is available in the ECW Technology WhitePaper available from Earth Resource Mapping (http://www.ermapper.com/).

From a compression perspective, the main significance is that the ECW technology quickly compressesvery large images, using small amounts of RAM.

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MrSID technology

The MrSID compressor uses DWT technology developed and patented (U.S. Patent # 5,710,835) in partthrough a project at the Los Alamos National Laboratory funded by the U.S. Government, managed undercontract by the Regents of the University of California. LizardTech has a commercial license to thistechnology, and the U.S. Government and the University have certain reserved rights in the MrSIDtechnology.

Unlike the ECW patent pending technology, the MrSID technology is based on older DWT technology,where the DWT is performed in an entire image at one time.

The crux of the invention used by MrSID to solve the problem of large files as the input file is broken into“tiles”. The DWT is performed on each tile in sequential order. The edge results from tiles to theimmediate left and immediately above added back into a given tile to ensure that the DWT results in aseamless overall DWT operation.

While this approach does indeed enable compression of reasonably large images, it suffers from somelimitations, particularly when compared to the ECW technology.

Because the MrSID DWT operation is performed on a tiled basis, the intermediate work-in-progress mayhave to be cached out to disk and then read back. This slows the DWT process, and places limits on theultimate size of the image that can be processed quickly. For example, to process a 1,000,000 x1,000,000 pixel (e.g. 1TB or 1,000GB) image at a 1Kx1K block size, the MrSID technology must eithercache 1Gb of input lines (1024 lines) in memory, or randomly write and read the tiles to/from disk whileprocessing.

Technology conclusions

The two approaches clearly show their origins. The DWT invention used by MrSID has it’s origins in thecompression of smaller grayscale fingerprint images, where as the DWT invention used by ECW hasorigins in the image processing expertise Earth Resource Mapping developed in processing large amountsof digital imagery with the ER Mapper product.

Both products are capable of decompressing selected portions of an image, enabling interactive roamingand viewing of images. The ECW technology is better suited to Internet distribution of imagery, as itfeatures progressive image transmission. This is reflected in the superior Image Web Server technologyoffered by Earth Resource Mapping compared to the Image Server offered by LizardTech.