[Oberon] FPGA - Grapes.Pict - structure

[Tomas Kral]

Hi,

I have made some progress, after holiday, in implementing `BitMaps.Mod'
for FPGA Oberon system. Currently restricted to B&W display only,
though I have some `VID.v' mods available for 3 and 4 bit colour.

Now I wish to take it for a test ride, I found a few B&W pictures from
ETH Oberon, namely `Grapes.Pict', and `Esher.Pict', I guess these may
originate in Ceres, possibly Alto systems. 

QUESTION
I need to learn internal structure of the Pict file, I wish to decompose
it to B&W bitmap planes. Reading the ETH code, I see there is colour
maps stored, along with WxH dimensions.

EDIT Ah, Now I also see `RLE' compression.

I particularly do not understand how color map is used, I can only
guess that instead of pixels, 0=black, 1-white, there is an index
to color map table stored for each pixel. 

I really need help, I am not very good at reading of Bachus Naurus
`EBNF', but could help a lot here, plus some examples.

Many thanks in advance.
Tomas 

-- 
Tomas Kral <thomas.kral at email.cz>