Image compression: ER Mapper 6.0 ECW v2.0 versus MrSID 1.3

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Emory Newton
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1 Image compression: ER Mapper 6.0 ECW v2.0 versus MrSID 1.3 With massive file sizes for digital imagery now commonplace, compression is a natural choice to shrink 100 s of GB of imagery down to a manageable size. This document compares two produces, Enhanced Compression Wavelet (ECW) v2.0 from Earth Resource Mapping, Inc. and MrSID from LizardTech, Inc. Both have been designed to compress, display, Internet serve and distribute imagery. As summarized in the following table, conclusions from the detailed comparison are: The ER Mapper ECW v2.0 compression is better quality, produces smaller images, is much faster, and has a larger user base compressing imagery. Both ECW and MrSID have the same price point, however the ECW v2.0 compressor is better value, as it is tightly integrated with image preparation functionality (orthorectification, color balancing, mosaicing, image processing, surface gridding and contouring, map production, vector rasterization and so on) that is lacking in the MrSID product. The ECW technology is an open standard, with both Decompression and Compression Software Development Kits (SDK) application integrate libraries available at no cost. There is only a decompression - no compression - SDK available for MrSID, which locks users in to a proprietary product to compress imagery. The following table provides a quick comparison (see the rest of the report for full details): Quick comparison ECW v2.0 MrSID 1.3 To compress 500MB images ECW Compress Free MrSID Professional $1,500 To compress unlimited size images ER Mapper 6.0 $4,950 MrSID Publisher $5,000 Maximum output compressed image size (WinNT) Unlimited 2GB Manufacturer recommendation for RAM needed to compress a 3GB image. 128MB 512MB+ Viewer for data distribution Yes, free Yes, royalty payments Compression requires hardware dongle No Yes Compression speed Good, 1MB/second Poor, 0.45MB/second Compression quality Excellent Good Time to roam and zoom to 4 image areas via Internet 12 seconds 108 seconds Open Decompression SDK library Yes Yes, restricted usage Open Compression SDK library Yes No Internet web server Yes, interactive progressive update Yes, limited functionality Internet, Office, GIS and CAD application support Yes Yes 1

2 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 development Software Development (SDK) toolkit available for both products, broken into the following sections: Test procedures- Procedures used to compare ECW and MrSID Compression Quality Usability Technology - Prices, functionality, speed, size of compressed images - Compressed image quality - Viewing speed, ease of use, product compatibility, installed user base, Internet usage and SDK availability - 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 also included. You can duplicate the comparison by performing the comparison yourself with the free ER 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 the property of their respective owners. 2

Test procedures Side by side comparisons were performed as follows: Software

evaluate compression results: The compressed ECW and MrSID images were tested

Analysis of image quality was examined at a variety of resolutions.

the speed to view and decompress images.

3 Test procedures Side 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, MapInfo and 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 the tests 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 3

A larger 100GB mosaic consisting of 2,000 files was to be included in the comparison, however the MrSID compressor was unable to compress the image as MrSID limits output compressed image size to 2GB

All source images were uncompressed RGB or uncompressed Grayscale TIFF format files. Compression was performed on a freshly started computer.

4 A larger 100GB mosaic consisting of 2,000 files was to be included in the comparison, however the MrSID compressor was unable to compress the image as MrSID limits output compressed image size to 2GB under Windows NT, so the large test was excluded from the comparison. Testing compression speed and quality Images were selected from a range of digital image sources. All source images were uncompressed RGB or uncompressed Grayscale TIFF format files. Compression was performed on a freshly started computer. No other application products were running during the compression tests, and multiple tests were performed to obtain average compression times. The DOQQ mosaic test was originally selected to compare the ability of both ECW and MrSID to mosaic images while compressing. However, MrSID is unable to remove image stitch lines or balance images (required to produce a seamless mosaic) and produced mosaics of an unacceptable quality. Therefore, the ER Mapper Balance Wizard was used to create a seamless mosaic as a single grayscale TIFF from the original individual USGS DOQQ, and this file was then used as the DOQQ input image for compression testing between ECW and MrSID. 8 x USGS DOQQ mosaic, unbalanced After balancing with ER Mapper Balance Wizard ER Mapper s Balance Wizard was used to produce a seamless DOQQ mosaic prior to compression For compression, no automatic clipping was selected. For MrSID, the manufacturers recommended tuning parameters were used for compression parameters. The ECW compression programs do not require any compression tuning parameters. Different compression rates were selected for each image, to measure quality of result in a range of applications. Sometimes quality is more important than image size, and in other cases compressed image size is more important. The comparison was designed to evaluate both of these factors. 4

5 Parameters used for compression The following table summarizes the input images and test results (full test results are provided in following sections) and compression parameters used, as recommended by the manufacturers. GB_AIRCOLOR 8 x DOQQ GRAYSCALE PHOTO Description 1GB Color airphoto 8 x USGS DOQQ's Grayscale orthophotos Scanned color 35mm Dimensions 19,167 x 19,215 x 23,844 x 9,249 x 7,145 x 1 2,048 x 2,896 x 3 14,775 x 1 3 Uncompressed size 1079MB 344MB 64MB 13MB Target compression ratio 40:1 20:1 20:1 20:1 ER Mapper ECW v2.0: Compression parameters None needed None needed None needed None needed Time to compress 1015 seconds 362 seconds 65 seconds 19 seconds Compression MB/second 1.06 MB/sec 0.95 MB/sec 0.98 MB/sec 0.68 MB/sec Compressed file size 13.0MB 16.4MB 3.1MB 0.4MB Actual compression ratio 83.0:1 21.0:1 20.6:1 32.5:1 Overview image quality Excellent Excellent Excellent Excellent Detailed image quality Excellent Excellent Excellent Excellent Geospatial image quality Excellent Excellent Excellent Excellent Color image quality Excellent Not applicable Not applicable Excellent Viewing speed Very fast Very fast Very fast Very fast MrSID 1.3: Compression parameters 6 levels, 1024 block 5 levels, 512 block 5 levels, 512 block 4 levels, 512 block Time to compress 2325 seconds 1140 seconds 99 seconds 58 seconds Compression MB/second 0.46 MB/sec 0.30 MB/sec 0.65 MB/sec 0.22 MB/sec Compressed file size 24.0MB 17.7MB 3.1MB 0.9MB Actual compression ratio 45.0:1 19.5:1 20.5:1 13.7:1 Overview image quality Poor Poor Poor Poor Detailed image quality Good Excellent Excellent Good Geospatial image quality Excellent Good Good Good Color image quality Excellent Not applicable Not applicable Excellent Viewing speed Very slow Slow Slow Slow 5

6 Compression Pricing and functionality Before compressing imagery, a range of image processing is required to prepare images for compression and 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 v2.0 Compression Wizard as one of the integrated mapping functions performed by ER Mapper) with the MrSID 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 Free Compressor and MrSID Professional). The inability of MrSID to integrate image compression with other image processing operations was found to be a substantial limitation. Comparison of product pricing and level of support provided Pricing ER Mapper 6.0 with ECW v2.0 MrSID Product to compress less than 500MB images Free (ECW Free Compressor) Product to compress any size images $4,930 (ER Mapper 6.0) Price includes 12 months support and updates Yes $1,500 (MrSID Professional) $5,000 (MrSID Publisher) No 6

7 Comparison of image preparation functionality Image preparation ER Mapper 6.0 with 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 Image formats directly read ER Mapper 6.0 with ECW v2.0 ALG, ERS, ECW, TIFF, GeoTIFF, JPG, DOQQ, LAN, ARC/INFO.HDR, Spot View. Many 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 to compression MrSID 1.3 Mosaicing Yes Limited Yes Seamless mosaics Yes No Color balanced mosaics Yes No Maximum allowed input image size > 1TB (1,000GB) > 100GB Maximum allowed compressed image size unlimited TIFF, GeoTIFF, LAN, ARC/INFO HDR, Sun Raster. No vector formats No 2GB 7

8 Compression speed to compress and compression throughput The 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 over 3 days to compress the same amount of imagery. As MrSID does not take advantage of multi-cpu machines, this compression comparison was performed on a single-cpu machine. On a dual CPU machine, testing of the ECW compressor showed it to be even faster, with a further 40% and 95% increase in speed. Compression Time in Seconds (smaller is better) Compression speed in MB/second (larger is better) Seconds MB/second ECW v2.0 MrSID 1.3 1GB_COLOR 8 x DOQQ GRAYSCALE PHOTO 0.00 ECW v2.0 MrSID 1.3 1GB_COLOR 8 x DOQQ GRAYSCALE PHOTO Chart 1: Compression Time in Seconds and Throughput in MB/second 8

9 Size of compressed images Both ECW v2.0 and MrSID generate compressed imagery by specifying a target compression ratio. This ratio 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 Quality section, the ECW v2.0 compressor consistently produced better quality results than the MrSID compressor, and did so in a faster time while producing smaller compressed images. ECW v2.0 MrSID Compressed image size in MB (smaller is better) MB GB_COLOR 8 x DOQQ GRAYSCALE PHOTO Chart 2: Size of compressed images in MB 9

10 Quality Image quality was compared using several measurements. Each image was roamed and zoomed into different 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. There were no cases found where the MrSID image quality was better than the ECW image quality. Quality of the color 1GB airphoto image ECW achieved a compression rate of 83:1 resulting in a 13MB file. MrSID achieved a much lower compression 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 and image detail, and the results were judged as very acceptable, other than the blurry overviews with the MrSID images. ECW retained a slightly high geometric accuracy and color balance. Uncompressed ECW Compressed MrSID Compressed 10

and the MrSID compressor achieved 45:1 for this image, so despite being of equal quality,

11 Image quality comparison for 1GB color airphoto It is worth highlighting that for a target compression ratio of 40:1, the ECW compressor achieved an actual compression rate of 85:1 and the MrSID compressor achieved 45:1 for this image, so despite being of equal quality, the ECW image is much smaller (13MB for the ECW image compared to 24MB for the MrSID image). 11

Quality of the grayscale 344MB DOQQ mosaic (20:1

compressed images of good quality, even at a

12 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 of 20:1, which is fairly high for grayscale imagery. Again, the MrSID image was slightly blurrier than the uncompressed or ECW image. Uncompressed ECW Compressed MrSID Compressed Image quality comparison for 334MB DOQQ orthophoto mosaic 12

Quality of the grayscale 64MB orthophoto

13 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 had slight 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 13

the MrSID image was slightly blurry at top-level zooms.

14 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 the MrSID image was slightly blurry at top-level zooms. Uncompressed image ECW image MrSID image Image quality comparison for Kodak Photo CD scanned 35mm photo 14

15 Observations During quality comparisons, the ECW format displayed noticeably faster, in all applications tested. For larger images, the speed difference was very significant - in some cases the ECW images displayed 10 times faster than the MrSID. In all cases, the ECW images displayed at least twice as quickly as the MrSID images. Some additional tests were performed at higher compression 50:1 compression ratios. The ECW format performed much better at higher compression ratios than the MrSID format, with much less blurring and less loss of features and definition, although this may not be that important, as the ideal compression ratios seemed to be in the 10:1 to 20:1 range for grayscale images, and 20:1 to 40:1 for color images to produce results that still had high definition, color balance, and clarity. 15

16 Usability Installed user base Earth Resource Mapping has developed and marketed the ER Mapper product for 10 years, with regional offices 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 ECW compression engine is included in all copies of ER Mapper 6.0. ER Mapper has a significant installed user base, is installed in over 120 countries and is supported by a world wide network of over 500 resellers. LizardTech, Inc. is a smaller company with an office in Seattle, USA. With a more limited reseller and support network, and being a younger company than Earth Resource Mapping, there is a smaller installed user base using the MrSID compression technology. Product support It is difficult to establish an exact comparison of products that support the ECW format and the MrSID format. Many of the products listed as being supported by MrSID are either beta versions of plugins offering limited functionality, or the products themselves were not released at the time that this comparison was performed. Both products support the major GIS products, and both offer stand alone viewers, ActiveX / ATL components, and web browser support. The ECW viewer (ER Viewer) is a freely available viewer than can be shipped with any imagery compressed with ECW format, at no charge. The MrSID viewer is also free for download, however data suppliers 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 MrSID product only supports web browsers to access remote imagery. Both products support web AutoCAD Map, ArcView, MapInfo, MapX, MS Office, Photoshop and web browsers. ECW has all common application interfaces: OLE, ActiveX and ATL. MrSID offers an ActiveX interface only. Currently there would appear to be slightly more released products that support the MrSID format in a final non-beta form than the ECW format. Four software companies contacted during this review indicated they would be supporting ECW in favor of MrSID because ECW offers both compression and decompression SDKs, indicating the situation is evolving rapidly. MrSID only provides decompression/viewing SDK s for applications. This means that all imagery must be compressed using one of the LizardTech MrSID compression products. The MrSID library only enables access to local compressed images - applications can not access to imagery served via the Internet using the MrSID decompression SDK library. Many software companies are justifiably nervous about depending on an external 3 rd party product for image compression. Given that the version 2.0 of ECW recently released by Earth Resource Mapping also includes a free compression SDK, and given the announcements already made by companies adding ECW support to their products, the number of products supporting the ECW format is expected to increase rapidly. 16

17 Internet usage Compressed 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 some simple 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 application software such as GIS products. The MrSID products only offer web browser based access of remotely served images. The remote access of a 60GB mosaic served with ECW s Image Web Server was compared with the remote access of a 2.6GB mosaic served with MrSID s Image Server (this was the largest MrSID image that could be found for the comparison - note that the ECW image being served is over 20 times larger than 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 to zoom 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 every respect. The lack of progressive image update, and the lack of real time roaming and zooming, were particularly limiting in the MrSID Image Server. 17

Note the progressive image update occurring on the ECW image, and note that the MrSID image does not update in real time, and leaves phantom image copies behind while

18 Comparison of image access via the Internet The following images demonstrate the difference between the two systems. The images were accessed from within Internet Explorer 5. Note the progressive image update occurring on the ECW image, and note that the MrSID image does not update in real time, and leaves phantom image copies behind while roaming, 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 the bottom-right corner (the blurry part of the image). MrSID image via the Internet after quickly roaming. Note the garbage phantom images while roaming. 18

19 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 Decompression performance: Multiple view roaming/zooming 22 seconds 82 seconds 12 seconds 108 seconds Supports progressive image update: Yes No ECW and MrSID both have decompression libraries to enable applications to add support for reading compressed imagery. ECW compression and decompression libraries to enable application developers to both read and create compressed image files. This is a significant difference between the ECW and MrSID market philosophies. 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 the ECW 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 into using a 3 rd party product, which is not desirable. Note, however, that the free ECW compression SDK supports a maximum input images to 500MB - the full ER Mapper 6.0 product must be purchased to compress images larger than 500MB in size. The ECW compression and decompression/viewing SDKs can be used by anyone can add image compression and decompression/viewing (even competitors to the ER Mapper product). On the other hand, the MrSID decompression libraries are restricted by LizardTech, and by their licensing agreements with the US Government on the technology. LizardTech will not license the decompression 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 imagery than the MrSID SDK. Tests performed during this comparison show that applications using the ECW SDK to view compressed imagery display or print imagery between 300% and 900% faster than applications using the MrSID SDK to decompress and view imagery. Given that a the final goal for compressed imagery is to enable quick access, this is a significant feature of the ECW SDK over the MrSID SDK. 19

20 Technology Both products compress by transforming images into wavelet space using Discrete Wavelet Transformations (DWT) and then quantizing and encoding the wavelet space images. Quantization reduces information 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 be compressed, 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 of RAM 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 use different techniques, which have important implications for the performance and capabilities of the products. 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 the dynamic algorithm compiler technology used by ER Mapper, which has been the basis for ER Mapper s success 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 DWT generation (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 very low 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 1,000,000 x 1,000,000 pixel image (e.g. 1TB or 1,000GB) with only 128MB of RAM required during the DWT process (additional RAM is required for the follow on quantization and encoding stages used to compress images, 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 does not have to break an image in to tiles before performing the DWT process, and the ECW process does not 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 wide range of applications not related to compression. For example, Mr. Nixon s DWT invention can be used to fuse images of different spatial resolution, by performing the DWT on the two images, adding the wavelet information together, and then performing the inverse DWT. The entire process performs in a pipelined fashion, with no intermediate disk files required. Other DWT applications for the invention include image enhancement and feature recognition. As these are beyond the scope of this comparison document, they will not be detailed here. Further information is available in the ECW Technology White Paper available from Earth Resource Mapping ( From a compression perspective, the main significance is that the ECW technology quickly compresses very large images, using small amounts of RAM. 20

21 MrSID technology The MrSID compressor uses DWT technology developed and patented (U.S. Patent # 5,710,835) in part through a project at the Los Alamos National Laboratory funded by the U.S. Government, managed under contract by the Regents of the University of California. LizardTech has a commercial license to this technology, and the U.S. Government and the University have certain reserved rights in the MrSID technology. 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 the immediate left and immediately above added back into a given tile to ensure that the DWT results in a seamless overall DWT operation. While this approach does indeed enable compression of reasonably large images, it suffers from some limitations, particularly when compared to the ECW technology. Because the MrSID DWT operation is performed on a tiled basis, the intermediate work-in-progress may have to be cached out to disk and then read back. This slows the DWT process, and places limits on the ultimate size of the image that can be processed quickly. For example, to process a 1,000,000 x 1,000,000 pixel (e.g. 1TB or 1,000GB) image at a 1Kx1K block size, the MrSID technology must either cache 1Gb of input lines (1024 lines) in memory, or randomly write and read the tiles to/from disk while processing. Technology conclusions The two approaches clearly show their origins. The DWT invention used by MrSID has it s origins in the compression of smaller grayscale fingerprint images, where as the DWT invention used by ECW has origins in the image processing expertise Earth Resource Mapping developed in processing large amounts of digital imagery with the ER Mapper product. Both products are capable of decompressing selected portions of an image, enabling interactive roaming and viewing of images. The ECW technology is better suited to Internet distribution of imagery, as it features progressive image transmission. This is reflected in the superior Image Web Server technology offered by Earth Resource Mapping compared to the Image Server offered by LizardTech. 21

Solving the problem of serving large image mosaics. Using ECW Connector and Image Web Server with ArcIMS

Solving the problem of serving large image mosaics Using ECW Connector and Image Web Server with ArcIMS A White Paper from Earth Resource Mapping 9 April 2003 Asia Pacific Regional Office Americas Region