Degas to BMP util ?

[exxos]

Hi all,

 

A mate of mine says there is a PC art program to convert degas Pi1 to BMP has anyone any idea what it is called ? If not does anyone have the file spec for degas files ? I pretty much know how they are structured but would need to know exacts before I could write my won.

 

Thanks!

Chris

[Gunstar]

Here is a link that has utilities for this type of thing as well as some "unofficial" versions of Neochrome (like Neochrome MASTER) which are far better than DEGAS, with everything it has, and more...(the original didn't allow 512 colors, these hacks do), I highly recommend it (Neochrome MASTER)! Any serious Atari ST artist uses this and Spectrum 512, but yes, the Pi1 to BMP utilities you want can probably be found here:

 

http://www.geocities.com/dahstra/atariarc.html

 

http://www.geocities.com/dahstra/atari.html (this is the main page)

[exxos]

Thanks for the reply, I use GEMVIEW at the moment to convert them on my ST though I was wondering actually if there was a PC program to do it :-

[Gunstar]

Sorry, in my search for a website that had something like your looking for I forgot exactly what you were looking for...I did find a site at some point that had a PC conversion program, but I couldn't find it again (I found it through site links the first time). By the time I actually found ANYTHING, I forgot that you wanted a program ro run on the PC and not the ST (got it backwards).

[Wrathchild]

Sounds like you need http://www.xnview.com

[exxos]

yeah t hanks, I came across that site yesterday infact ive not looked at it yet. I found another one called "the atari picture viewer" which does a few common formats!

 

Chris

[LinkoVitch]

For anyone interested in the file format for Degas PI1 it's DEAD simple

 

offset:

 

0-1 : some value that deffines type pof PI file (1,2, or 3)

2-35 : The colour palette copied straight from the registeres of the shifter. 2-3 is the colour for colour0 etc

36 - end : The image data dumped straight from the screen memory.

 

Same is for PI2 and PI3 but obvioulsy not all colour registers are used.

 

easy huh

[exxos]

Writing a PC program is hard to convert it though. There is no information about how the actual screen data is stored which makes it hard. I have a program which I am trying out which almost gets the image from a Pi1 picture though its got white lines ni it and I can get all kinds of odd problems.

 

Chris

[LinkoVitch]

exxos the makup of the screen is easy too (guess who used to spend a lot of time in an assembler ) just hope I can explain it for you..

 

OK, I'll deal with lowres. The ST's screen uses bit planes to represent the screen, in a low res screen there are 4 of these planes. Each chuck of plane data is 2 bytes in size and these are interleaved next to each other... so starting from offset 0 in screen memory, and given that each plane is 2 bytes the data is arranged like so:

 

0-1 - Plane 0

2-3 - Plane 1

4-5 - Plane 2

6-7 - Plane 3

8-9 - Plane 0

10-11 - ...... until the end of the screen

 

Now a plane block is made of 16 bits (2 bytes, 8 bits each, 16 bits). Each bit represents 1 pixel on the screen, working left from right most significant bit is the left most pixel.

 

To work out what colour a pixel should be on the screen you need to look at all four planes. In low res, each block of 4 planes represent the same 16 pixels, you need all 4 to work out the colour index. It is done very simply.. if we concentrate on pixel 0, we need the MSB from plane 0,1,2, & 3 If you write these down in that order plane 0 MSB and plane 3 LSB you will end up with a 4 bit integer. Now whats the largest number you can store with 4 bits? 15, so a range of 0-15 is possible, so 16 values.. and how many colours in low res on an ST? 16! now isn't that a coincidence!

 

So by combining the bit planes like this you are given the colour index (in the pallette) of that pixel. Quick look at the pallette and you can find out your colour, and away you go.

 

Hope that makes sence to you.. any questions let me know

 

/me glad to be making use out of the stuff stored in his head