education re zipping and compression

  hatrickj 09:00 12 Jun 2004

I have two fokders of pictures, the original is 33.9MB and its zipped version 33.8MB which to me seems very little gain as I want to email to someone and even on BB that is a long transmission. In the advanced properties box of the Windows viewer thre is an option to compress to save space but having experimented with it there is no evidence of the file size reducing. Files are jpeg, Any advice about the use of zipping and compression is welcome. Do, for instance, they work more effectively with other file formats, what realistically can be expected in size reduction without too great quality loss?

  Falkyrn 09:12 12 Jun 2004

Jpeg files are already compressed that is why there is so little difference when you try to zip the files.

Depending on the type of file that you "zip" there can sometimes be a considerable space saving but with precompressed formats such as jpegs any gains are minimal if they exist at all.

  Pesala 11:03 12 Jun 2004

It has batch conversion facility. You can save all files again with a higher compression ratio. Experiment with one image first to get a satisfactory results. JPG compression is highly efficient. Then zip the whole lot, just to keep them in one attachment if you prefer, though one can attach several JPGs to one email. Sending several emails with 1 to 5 attachments may be better than send just one email with 10 Mbytes of attachments.

click here for download

click here for my help website

  Falkyrn 22:00 12 Jun 2004

As Pesala has said using a graphics program to resample the jpgs can result in greater compression and therefore smaller file sizes.

A lot depends on what you want the images for ... if they are being sent for viewing onscreen or for web use (for example) then you can use pretty hefty compression on them and gain a dramatic reduction in file size.

If however you want the person on the other end to get the best quality then you are limited in the compression available to you.

  Valvegrid 22:13 12 Jun 2004

I doubt there are many inboxes that will accept that size file.

Alteratively, if your ISP is offering personal web pages, some of them are about 50MB. Set yourself up a personal web page and upload it and give the address to the recipient so they can download it later at their pleasure.

  Pesala 22:21 12 Jun 2004

For example:

Hubble deep space image

TIFF format 113,634 Kbytes (original image)

PNG format 83,949 Kbytes (no data loss)

7-zip archive format 78,211 Kbytes (no loss, better than zip format)

JPG 417 Kbytes (sic) 10% quality, considerable data loss, but still pretty good click here

  Pesala 22:28 12 Jun 2004

Though it won't take long to download, your PC might grind to a halt trying to resize it in Internet Exploer. Better turn off image resizing in options first if you want to look at it.

  hatrickj 16:41 18 Jul 2004

As phone has been down a long time-BT fault- I haven;t returned to subject but the kinks you gave failed 404 file not found. Is there a corrected link?

Not quite on same subject I posted 'advice needed on jpeg compression' in connection with compressing to format 4:2:2 or 4:2:0, but with no response yet? Any advice there to be had?

  Pesala 21:44 18 Jul 2004

Shortly after posting the above links, NTL closed my old account so I had to change my user name. Hence the broken links.

Irfan View Tutorials: click here

Hubble Deep Space Picture: click here

I don't know the answer to the 4:2:2 format question. In Corel Photopaint the default subformat is 4:2:2 with an option of 4:2:4, but I haven't a clue what it means.

  Falkyrn 22:14 18 Jul 2004

4:2:2 is the standard setting in Corel for "downsampling" when saving jpeg images the other settings are usually 4:4:4 and 4:1:1

More info on image compression can be seen at click here

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