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The owners poehali.net and poehali.org are to be commended for collecting a huge number of USSR General Staff maps and making scans of them available to the public for free or at low cost.

However, the quality of the images served is very low as a consequence of the loss of information from the images, caused by distributing the scans as .gif files. This has commonly caused substantial degradation of the image quality, resulting in a blurring of closely spaced lines such as contours and making some feature names unreadable. This obviously limits the usefulness of the maps.

In the geographic information industry, storage distribution of large image files is a problem. However, file formats and image compression algorithms are available that will allow large files to be compressed to small file sizes with hardly any, or minimal loss of information from the image.

One of these losslesss image compression algorithms is freely available, allowing the compression and decompression of image files, provided the decompressed image is less than 500Mb.

This technology is called Enhanced Compressed Wavelet and more recently, JPG2000. The algorithms were developing by Earth Resource Mapper (ER Mapper) for the storage and distribution of large satellite images or mosaics of images, some over 100Tb in size. Freeware required for image compression/decompression and viewing the imagery (as a compressed image) is avalable from

http://www.ermapper.com/downloads/plugins.aspx

From there, download:

ER Viewer 7.1

http://www.ermapper.com/downloads/download_view.aspx?PRODUCT_VERSION_ID=304

and

Free ECW JPEG 2000 Compressor 7.0

http://www.ermapper.com/downloads/download_view.aspx?PRODUCT_VERSION_ID=266

Other free plugins and SDKs are available for Adobe Photoshop and Microsoft products or to integrate into other software.

To give an example of what can be achieved, I compressed a 1:200000 USSR General Staff map of part of Africa, using different ECW compression ratios.

This map was scanned at 300dpi and is 6807 * 5105 pixels. As a .tif file it is 135Mb. As a .jpg file using low image compression it is approximately 10mb.

Usiing the ECW/jpg2000 image compression algorithm, with a compression of 10% it is 12Mb and appears identical to the tiff.

Using 50% compressiong the image is 4Mb and only at very high zoom is a slight loss of information noticable.

At 75% compression the scan is 3Mb and although there is greater loss of information, this is only noticable at high zoom.

All this is achieved by keeping the scan as a 24-bit colour image.

So what do i recommend?

I have explained above how large image can be compressed to a file size that allows them to be distributed over the intenet and stored economically. This method unlike the procedure being used at the present, results in images of superior quality and therefore makes them very much more useful.

I hope the owners of this website have kept copies of the original scans. If so, I recommend the original scans are compressed using ECW image compression technology using 50% image compression and that map scans are distributed as .ecw files. If recipients of these .ecw files then want to decompress and convert them to .gifs or .jpg files or whatever, they can. Correspondingly, I recommend that you discontinue storing and distributing your collection of scanned maps as .gif files.

However, modern geographic information systems (GISs) do not need to decompress .ecw files to view the contents. I very low cost GIS that can do this (and much more) is Manifold System GIS from www.Manifold.net, the cheapest version of which is 125 US dollars. I use this and recommend it. Incidentally, it is a product of Russian immigrants to the USA. ;D ;)

If anyone wishes to discuss this subject, I can be contacted at nicholasverge@dsl.pipex.org

Best regards,

Geo

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So, is it the same as Jpeg2000 compression format (.jp2)? It seems that, thought it has been developed several years ago, it did not become widely popular over Internet, at least at the moment. One reason, as seems to me, is that conventional browsers do not have built-in support for it (however, with the Shockwave Flash the same statement is true, which does not hinder its popularity).
As for maps from this site, I also would like them to have been stored in greater resolution. But, if I compare files from poehali.org @200dpi with the same map squares that I have @300dpi, I do not see any significant loss of detail. At least all names are readable, and virtually all isolines are distinct, either. However, some squares with lower resolution (150 or even lower) are definitely bad.

The conclusion is that, in any case, the maps currently stored are mainly without sources (with margins, in full res. etc), or, at least, are not likely to be reprocessed by the site owners. It's a bit pity, but I think that the current state is good enough for being usable for practical purposes, provided that you are not an absolute perfectionist : )

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and yer more comment: Jpeg and wavelet formats, for my opinion, are less suitable for geographic maps than simple gif, because the latter does not blur lines (and as for 256 color limit, is seems sufficient). Certainly if you set compression ratio to be really mild, lines are not blurred in jpeg either, but the size will be comparable..