Hi,
Some answers and explanations:
I tuned in an already running fax signal... couldn't see how to start reception.
Please click "Skip APT" for the initial APT start, then, click "Skip
phasing". It will then start decoding. You might then recenter the image
(The phasing step is done for detecting the beginning of lines).
The following are the basic features you need for a fax system:
1) manual start/stop
2) auto start/stop (switchable option)
"Theoretically", it starts automatically when an APT start sequence is
detected. I do not know how to enhance the process at the moent. Maybe a
better filter. The APT frequency has some margin, but if it is too
large, it starts decoding each time 300 hz is detected in noise. So, the
method should be refined.
3) auto home to top (switchable option)
If the end of an image is detected, it is saved in a file (Whose name
contains the date/time and the frequency, by default in the directory
$HOME/.fldigi/images just like MFSK image files), and the image is emptied.
3) manual shift of received image and concurrent adjustment of
sampling location to align edges.
The slider "Center" should do that, if I have understood what you mean.
I am thinking about automatic unslanting but first would like to make
basic things work.
4) fine timing trim to get the edges straight (fax is synchronous,
computers differ enough to screw it up.)
The "LPM" widget can be fine tuned (Small arrows) to reduce the slant. I
agree that theoretically LPM (Lines per minutes) should be accurately
set. But, in the HAMFAX code I started from, the LPM was automatically
detected and adjusted using the first phasing lines. I reused the
detection of the LPM (60/90/120) but removed its fine adjustments
because it was not accurate enough to suppress the slant. So I
prioritized the idea of manually fine-tuning it in order to have a
vertical image. I understand this could be put in question.
5) zoom control from about 320 wide to full width.
If LPM=120 which seems to be the most common cases, the width in pixels
is 904. Initially, given the usual screens width, I displayed faxes "as
is" using the existing "picture" class.
I can certainly add zoom in/ zoom out buttons. Is it what you mean ?
6) line mode (threshold the signal to b/w at 1900 hz)
OK.
7) grey mode - linear grey levels from black (1500 hz) to white (2300 hz)
OK. This is the current mode, no ? I was althgough thinking about
applying image enhagcement filters on -the-fly, but hesitated because
this can be done with image editing tools such as Gimp or Photoshop, and
chose initially to focus on pure "radio fax" features.
8) reception to memory so display is never a restricting factor on
resolution or sample rate
There is not limit on the height of images: I just add a hard-limit of
10000 lines because no reasonable fax should have this size (Most are
about 1300 lines). When this size is reached, an image file is saved and
the image cleared.
From there, a plug-in system for image processing operators would be wonderful.
Yes, I was thinking about adding xml-rpc calls.
The displayed images and the file captures are stretched in the vertical
dimension. Circles appear quite egg-shaped. This may be more related to the
station I was receiving than the program itself, but it would be cool if
there were some way to compensate for that.
This is right, I will work on this. Again, I wished at first stage to
focus on pure fax features
All fax uses square pixels. Sub-sampling of the received data is
required for correct display at any ratio other than 1 fax pixel = 1
display pixel.
OK. I noticed the same problem when sending an image and receiving it
with another fldigi process, both connected with jackctl.
Thanks for these remarks !
RC
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