Compression and Decompression of Files using Visual Basic 2005: ASP Alliance

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Compression and Decompression of Files using Visual Basic 2005

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by Abhishek Kumar Singh
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What are the types of Compression?

In general we divide compression algorithms in two types:

1. Lossless Compression

2. Lossy Compression

Lossless Compression

In lossless compression, the algorithm does not lose any part of data. It means exact source data should be generated after decompression. In business communication we use lossless compression for text based data/information. Lossless compression should be used to compress executable programs. The major purpose, as well as challenge, for lossless algorithms is to compress data as much as possible and get back the original data by taking minimum time.

Lossy Compression

In lossy compression, the algorithm does some loss of data to achieve higher compression. You do not get exact original data back in lossy compression. This compression works on those data in which some fidelity is acceptable. Picture, audio or video format data are usually compressed with lossy compression algorithm because among these some loss of data can be tolerated. Graphical image can be compressed either as lossless or lossy method depending on the requirement.

Now, there are various lossless encoding schemes (e.g. run-length encoding, Lempel-Ziv (LZ), Huffman, Deflate, GZip, TTA, FLAC, etc.) and lossy encoding schemes (e.g. MPEG-2 codec, psychoacoustics etc.).

Among these I am going to describe the DEFLATE and GZIP compression and its implementation in VB 2005.

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User Comments

Title: Compression
Name: Stacy
Date: 10/2/2008 4:24:41 AM
Comment:
Hi,

I am working on an asp application and I have a string that needs to be passed from script file to asp page, but the string breaks coz of its large size.Can this function be used for the same.Also how do i convert string to byte.

Please reply soon

Title: compression
Name: mike
Date: 9/4/2008 5:31:06 AM
Comment:
it can't comprees large file...65k is the limit..i hv tried compressing 90k file(TXT FILE)..bt to my surprise the compressed file is showg a larger memory thn its initial size..and there is no or a very little difference between gzip and deflate.am i doin any mistake here.?.plz help!!!

Title: compression
Name: Jeevitha
Date: 8/29/2008 9:39:38 AM
Comment:
Nice Article. It's very useful to me. Thanks a lot.

Title: Compression and Decompression
Name: Padma
Date: 5/29/2008 2:25:36 AM
Comment:
Article is very good....it helped me a lot...can u give article abt transferring an image file in vb6 using udp protocol....
mailid:belpadma@gmail.com
PH:080 22195854

Title: Senior Programmer/Analyst
Name: Guillermo
Date: 5/14/2008 10:23:12 AM
Comment:
I am very thankful for this article because it helped me very very much...

Title: Senior Programmer/Analyst
Name: J Eaves
Date: 5/12/2008 11:58:09 AM
Comment:
Great article and easy to follow. However, 2 issues. 1)I couldn't get code to work with CompressData() as MemoryStream. And 2)After I created a zip file and tried to open with WinZip 11, I get the following error "Cannot open file: it does not appear to be a valid archive."
Does anyone have thoughts or suggestions.
Thanks.

Title: Compression and Decompression of Files using Visual Basic 2005
Name: Gary
Date: 3/12/2008 10:38:09 AM
Comment:
omg thank you. MSDN sample is complete shite in comparison

Title: Compression and Decompression of Files using Visual Basic 2005
Name: Cammie McGinty
Date: 1/27/2008 3:04:27 PM
Comment:
Thank you for a clear and straightforward example.

Title: Reply to: Bloated results
Name: Abhishek (Author)
Date: 11/21/2007 2:58:05 AM
Comment:
hi Jacob,
BTW which type of files you are trying to compress and decompress?
Are you using the byte counters properly if you are not decompressing entire compressed file at a time?

Title: Reply to: Give me idea
Name: Abhishek (Author)
Date: 11/21/2007 2:55:50 AM
Comment:
Hi Netra,
sorry for late reply, i had stuck in some stuff.
You can achieve entire folder compression using DeflateStream but for this you have to implement your own logic to compress each file one by one inside the folder and then you can make a bundle of all compress files and also there should be a information file which should keep details of each file name, size etc which you can use while decompressing.
Frankly saying i have done this by myself but had some finding on this.
hope it helps you. If you got anyt idea on this please let me know. I will be thankful to you.
thanks.

Title: Bloated results
Name: Jacob Kennedy
Date: 11/2/2007 5:29:13 PM
Comment:
I'm implementing your DecompressByte on a folder of files that were zipped using GZipStream, and it's working a lot better than what I had, but my decompressed files are ending up over a hundred times bigger than the original non-compressed files... any ideas?

Title: Give me idea
Name: Netra
Date: 10/22/2007 5:26:55 AM
Comment:
Hi abhi,
i want to zip the folder containg files for eg. i have folder named ABC and in that folder i have 3 .txt files , i want to zip that ABC folder not only the files in that.
Can i done it at runtime , plz give me the idea. And i want to do it by using DeflateStream.

Title: Excellent idea....
Name: Rajiv Tripathi
Date: 7/5/2007 3:40:00 PM
Comment:
Hi Abhi,
That's a really gr8 idea. Thx for sharing it with all of us.That has helped a lot. i hope you remember me by my name, I implemented your idea and it produced remarkable result.
thx & all the best!!

Title: rijovg@gmail.com
Name: rijo
Date: 6/28/2007 6:23:07 AM
Comment:
i need an help would u plz contact on this id

Title: Re: File Extension
Name: Abhishek Kumar Singh
Date: 6/15/2007 7:52:18 PM
Comment:
As the gzipstream and deflatestream are stream based classes, one way would be- you can add file exetension in byte() at first/last position before compression. Then read those bytes to get the file extenstion and remove those bytes before writing the file.
Usually you need to know the extension of file by any mean while writing decompressed file. If compressed byte() are being transferred using remote methods you can send file extension as extra parameter in the method.

Thanx.

Title: file extension
Name: Theuns
Date: 6/14/2007 10:45:01 AM
Comment:
How do you keep the file extension when compressing it?

Title: My Feedback
Name: Sunny Adeshara
Date: 6/8/2007 8:53:00 AM
Comment:
I am very thankful for this article because it helped me very much.

Title: Good Article Keep it up
Name: Anjaiah Keesari
Date: 5/24/2007 9:05:54 AM
Comment:
Even I am working on Compression and Decompression with C# code your Article is very good. You Explained concepts very nice thanks keesari_anjaiah@yahoo.co.in

Title: I m proud of my best frined
Name: Vinit Pratap Singh
Date: 5/23/2007 9:13:57 AM
Comment:
Hi... i don't know Visual Basic.. but i think its a very big implement by you.. i m very proud of u.. keep it up... with lots of new adventure.. . vinitpratap@gmail.com

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