[Oberon] ETH - RLE compression

[Tomas Kral]

Hi,

I am looking into ETH `Picture.Mod' module. Please consider the
following code excerpt decoding `RLE' sequence. 

 c := P.height;
 WHILE c > 0 DO
    Files.Read(R, ch); k := ORD(ch);
    IF k < 128 THEN
      REPEAT
        Files.Read(R, ch);
        Bitmaps.PutPix(b,ce,ch,d);
        IF b>=ce THEN ce := ce-P.wth; b := a-P.wth; a := b; c := c-1
END; k := k -1;
      UNTIL k < 0
    ELSIF k >= 128 THEN
      k := 257 - k;
      Files.Read(R, ch);
      REPEAT
        Bitmaps.PutPix(b,ce,ch,d);
        IF b>=ce THEN ce := ce-P.wth; b := a-P.wth; a := b; c := c-1
END; k := k -1
      UNTIL k < 1
    END

=============================

QUESTIONS:

I wish to know how `RLE', `start' and `end' are identified? 
What is encoded in single bytes in each run, as we read by bytes?
Why we set a single pixel from a byte, instead of the whole bitmap word?

Many thanks in advance. 

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