I Have Two Questions Regarding The Comparison Of An Original Image File Format To The Resulting  Decompressed Image File Format In Terms Of Image Quality Resolution And Image File Size?

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Hello. I have a question to ask. This applies to programs applicable to my Windows 7 64-bit operating system.

For years, like all of us, I have used programs that allow you can compress (package) and decompress (unpackage) specific file format types (example: popular image file formats like raster formats such as JPG, TIF, PNG, GIF, BMP, RAW) using various file compression utility programs like WinZip, WinRAR, and 7-zip to name a few.

Questions – please answer both:

1. If I compress a popular raster image file format file using any one of these file compression utility programs and then decompress it later on, will that decompressed raster file format still have the same resolution and same file size like it was before it was compressed or not and 'some limited loss' will occur after image file decompression? Please explain.

2. Yes, I could perform a simple test or experiment on a image file format by comparing the original image file format resolution and file size to the final resulting decompressed image resolution and file size myself;  however regardless of the results (and especially the case if they ARE the 'same' in terms of resolution and file size), there may be something I am not aware of at a more technical level that I may of lost (or less likely gained) comparing the original image file and the decompressed image file. If so, please explain. (Yes, question number 2 is much like question number 1; however looking for OTHER technical issues at work, if indeed there are any.)

Please reply.

Thank you!
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The answer to questions 1 and 2 are basically the same.  You will encounter absolutely no reduction in quality after decompressing a file or collection of files.  Think of compression using this method as a form of encoding.  A requirement of these programs is that they must be able to return the encoded file(s) to the original format, just like decoding a message.  The compression is possible because typically, the data breaks down to binary, just a bunch of 1's and 0's.  In this case, sequences of 1's and 0's that are very similar can be represented in a slightly different way that takes up less space on disk.  Because the algorithm knows how it got the different representation of 1's and 0's, it can put them back in the correct sequence without too much trouble.  Bit-level error correction is also typically used.  The level of compression typically correlates with how much time the algorithm is allowed to spend analyzing the file and the level of variation in the file.  So typically, high resolution images in lossless formats do not have too much room for compression anyway.  

Here's a wikipedia link to learn a little more about data compression.



@ illusivefingers:

Hello. Nice to meet you.

Thank you for your comment.

Your comment is a well written and easily explained answer I can completely understand.

Thank you very much!!!

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