Actually there is a commented source code on Simon's web. The viewer is
quite straighforward, all the colour magic lies in the converter. ;-)
I am now planning to create a zx81 emulator, and that computer is quite
interesting in that it doesn't push all registers to stack on interrupt. It
means that some registers can't be generally used when interrupt is enabled,
but the benefit is that the interrupt handelr routine is faster to start.
This zx81-way it would probably be possible to change more colours per
scanline.
That brings me to the question if there exist 64bit TASM compiler. I always
used TASM with Z80 mactors to compile my programs, but now I can't run TASM
because my version is apparently a 16bit exe from MS-DOS. I would probably
need to find at least some 32bit edition, if that's possible. (I don't have
any experience with Python and I am not generally happy to install Python in
order to run Z80 crossassembler once in a while.)
A.
-----Původní zpráva-----
From: Thomas Harte
Sent: Tuesday, April 03, 2012 12:58 AM
To: sam-users@nvg.ntnu.no
Subject: Re: SAM HAM viewer
I've seen something similar on the Atari Lynx, which also has a 4 bit
frame buffer, the only difference being that I think that used a tight
loop of something like (i) load next palette index, next colour and
next delay length; (ii) push colour to palette index; (iii) perform a
busy loop of the desired length; (iv) repeat. The loop was
synchronised once with vertical retrace and timings were such that a
degenerate case was to change the entire palette once after every scan
line but you could instead, say, change a single palette index several
times over the course of a single scan line, or anything in between.
A better adaption for the Sam might be to allow palette and mode
changes, and for simplicity to add a delay length that just means to
wait until the next vertical retrace? If you have portions of the
image with only four colours (especially once the colour aliasing
forced by the 128-colour palette is accounted for) then switching to
mode 3 for a portion of a line could be the smarter thing to do, and
would presumably cost basically nothing to implement?
In terms of image conversion, I guess a heuristic would be the thing.
It feels like, even at Sam size, an exhaustive search could take
forever.
Of course, I didn't disassemble Simon's fantastic work so it's
possible he's way ahead of me on this one.
On 1 April 2012 18:05, Aleš Keprt <a...@keprt.cz> wrote:
Oh yes, this is nice. I saw similar things in the past, AFAIR this was
published on some disk magazine back in 90's. But it will be hard to find
it
now.
So how many colours are possible per line in this format? Or what is
possible in this picture format?
Also, I think that the converter could possibly de-noise the picture
before
or after the conversion. Or something like that. Because there are too
many
dots visible in places where there should be no dots. This is good in high
resolution graphics like when printing on printer in 600 DPI, but doesn't
look too well on Sam. Especially in emulator with crisp LCD display. ;-) I
think the whole de-noising process is extremely important when converting
to
low resolution and low bitdepth. And each single picture needs a different
values for the algorithm, so maybe there should be some kind of WYSIWYG
editor or something where users could change some settings and see the
result immediately in order to find the best settings for each file. ;-)
Maybe a genetic algorithm could help to find at least some local optimum.
/---
Aley
-----Původní zpráva----- From: Simon Owen
Sent: Saturday, March 24, 2012 3:10 AM
To: sam-users
Subject: SAM HAM viewer
Hi all,
I've been experimenting with HAM-style tricks on SAM, to try to improve
the quality of converted images. I've aimed to modify as many colours
as possible between lines, rather than using the traditional compromise
static palette. Are there any viewers using that technique already?
I've written a Python script to convert regular images to a new .sham
format, and a SAM viewer program to display them.
Demo: http://simonowen.com/sam/shamview/shamview.dsk
Source code: https://github.com/simonowen/shamview
You might recognise some of them as SAM or image processing favourites!
It still needs work on the dynamic palette selection, which just uses
the most-frequent colours, rather than doing proper quantisation. I
left the crayons image as an example of this breaking down.
Si
-----------------------------------------
Mgr. Aleš Keprt, Ph.D.
private: a...@keprt.cz, www.keprt.cz
office: Moravian College / Moravská vysoká škola Olomouc,
ales.ke...@mvso.cz
-----------------------------------------
Mgr. Aleš Keprt, Ph.D.
private: a...@keprt.cz, www.keprt.cz
office: Moravian College / Moravská vysoká škola Olomouc, ales.ke...@mvso.cz
