asking for clarification

MG
Posted By
mythreyi.g.1ve4ly
Sep 15, 2005
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348
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Hi,

i have a image which is compressed in PNG file format i need t compress it still more but the file size is increasing instead o decreasing, i want to know why is this happening. Iam using "ADOB PHOTOSHOP", "XAT.com (Professional Image Compressor). i want to know is there any other software other than these softwares. If its there then kindly let me know.
And also i want to know why does the file size increases when it i compressed still more.

And also when the same file is saved without altering anything, (jus opened in photoshop and saved it), then also the file size i increased, why is this happening? if any one knows the solution fo this then kindly let me know.

thankyou
mythrey

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Rainer Latka
Sep 15, 2005
mythreyi.g wrote:
Hi,

i have a image which is compressed in PNG file format i need to compress it still more but the file size is increasing instead of decreasing, i want to know why is this happening. Iam using "ADOBE PHOTOSHOP", "XAT.com (Professional Image Compressor). i want to know is there any other software other than these 2 softwares. If its there then kindly let me know.
And also i want to know why does the file size increases when it is compressed still more.

there are two different approaches to compression and their application depend on your needs:

Lossless compression permits to restore the original information (image, in your case). There are different compression methods, and the degree of compression depends on the (mathematical) strategy they follow (but also on the type of information to be compressed, e.g. images vs. music). When you apply compression twice, in simple words the following happens (I’m using a very simplified compression method for this example – there are of course more efficient ones): in the first step, repeating information is replaced by one instance of this information plus a count, how often it is repeated (think of an area in an image where all the pixels have the same colour). After this step, your file no longer contains repeating sequences which you could compress using the same strategy. So, if you now try to compress it again, the file is actually growing, since – in simple words – you have to add information to the file which will later be needed to tell the decompression method about this special situation.

If you want better compression you have two alternatives: find a different compression method that works more efficient (of course there are limits to this; if you want lossless compression, the original info needs to be in the file, somehow), or you accept information losses. In this case you will have to find a compromise on how much loss you are prepared to tolerate. Depending on the approach, lossful compressions may reduce the number of colours in your image (replacing some by "similar" colours), eliminate fine details or apply other strategies. Note that compression methods may also introduce artefacts which have not been in the image before. Just experiment with different degrees of compression when you store images in the jpg format.

HTH
Rainer

And also when the same file is saved without altering anything, (just opened in photoshop and saved it), then also the file size is increased, why is this happening? if any one knows the solution for this then kindly let me know.

thankyou
mythreyi

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