QL compression

[stevepoole]

Hi Folks,
There has been a lot of discussion in science magazines recently about compression codes.
Many codes have now been freed of patent restrictions, due to their age.
With so much interenet activity, the network would be gratified if even the ooccasional bit could be saved...

I am toying with some compression routines for the QL, using 'lossless' descriptions, but wonder if there have been any programs released previously to tinker with ? (Huffman, Zip, etc, etc). 'Improvements' I have been able to make have been at the expense of some ASCIIs...

With enegy savings being the order of the day, all comers are welcome. Thinking caps on !

Regards, Steve.

[ones' complement]

Bookmarked this a while ago: https://www.bigmessowires.com/2016/05/0 ... mpression/

Also, IIRC, the SMSQ sources have Q40/60 ROM compression/decompression routines.

[stevepoole]

Hi Ones Complement,

Yes, your site info is interesting, as it reveals the complexity of the subject.

The problem is made more complicated by the ever more pressing need for encryption !

There would appear to be no one solution for all cases.... as computers adopt increasingly more sophisticated softwares.

Perhaps we should make do with less bells and whistles, and use simple interfaces again.

Maybe we will not have the choice soon ?

Steve.

[Derek_Stewart]

Hi Steve,

If you are talking about, QL Archivers like: Infozip, RAR, HAR, LHQ, LHX, LHZ, ...

[stevepoole]

Hi Derek,

Is the code for these programs free to study ?

Steve.
_________

[Derek_Stewart]

Hi Derek,

Is the code for these programs free to study ?

Steve.
_________

Have you tried looking on the QL Homepage ?

https://dilwyn.qlforum.co.uk/arch/index.html

[stevepoole]

Hi Derek,

Thanks for the link ! I will take a look at the various methods over the next few days.

In the meantime, here is my minimalist attempt at compression-encryption.

It could be improved still further by crunching the binary stream.... (but does require the private-code table to be communicated).

Let Bp=1 to transmit the 'morse' signal as of yore.

Steve.

Pseudo_Morse.zip

(1.15 KiB) Downloaded 30 times

[stevepoole]

Hi again,

HELP ! Jan Bredenbeck's compact.zip gets supressed when downloaded, as it is 'not frequently accessed'.

Perhaps jan will put it on the Forum please ?

Steve.
_________

[dilwyn]

Perfect example of legitimate software being blocked by Windows, while the c**p gets through. The price we have to pay for the naughty people on the internet.

If you trust the site you got the download from, in Windoze 10 do this:

When it says "<filename> isn't commonly downloaded. Make sure you trust <filename> before you open it.", click on the '...' to the right. Then click on KEEP. Then SHOW MORE in menu that appears. Then KEEP ANYWAY.
When the download has finished, you can click on OPEN or SAVE AS (depending on what you were intending to do).

[qbits]

Hi,
Interesting subject QL Compression as for encryption not I suspect the real point of this dicussion but for limited short text check out my Enigma program. Skip over to Help for NEW Users and my QL Tinkering Post to take a look.

I have been working on a Special Addition to my QBITS BITMAP Design and have been looking into _bmp file formats. The simplest _bmp compression is Palette reduction using a single byte per pixel, 256 colours mapped to a Palette that is part of the bitmap file header where each holds a 24-bit colour for each entry. A program could select out of a full spectrum for the best display of the image. Using this in mind I have chosen the SMQL/E colour schemes COLOUR_QL and COLOUR_PAL bearing in mind for backward compatibility QDOS uses a 256 colour scheme Prime colours, with background contrast and a stipple.

Lossy where a set number of columns repeat the same colour, but might have just one or two changes and are hard to recognise by the human eye, these are absorbed hence the term lossy. It can greatly reduce a file size but is determined by the lossiness, ie. compression level set by the scheme and quality of the decompressed image required.

Finally Lossless this where an image is compressed without losing any of the information but can take a while to execute. It removes unwanted information and does not necessarily reduce the image file to any great extent.

So back the the experts...
QBITS