SSTV picture/file generation.

Forum for discussion of SSTV topics. Slow Scan television (SSTV) is a picture transmission method used mainly by amateur radio operators, to transmit and receive static pictures via radio in monochrome or colour.

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SSTV picture/file generation.

Postby Steve Anderson » Thu Oct 28, 2021 4:35 pm

It seems that John's/Chris's Triple-Pic up-convertor is coming nicely to fruition, how about picture/file generation?

For the SSTV audio files I generated some years ago I knocked-up a .tiff file to .wav file convertor.

First you took your original colour .jpg, artistically cropped it, resized it to 256x256, converted it to greyscale, and saved it as a .tiff file. For this I used Irfanview, a freebie download which is more of a viewer than editor, but performs all we need for this. Though you could use something heavy-duty to do the same job, e.g. Photoshop.

This you fired at the convertor, which would output 120x120 or 128x128, at either US or EU rates. All at baseband and simultaneously with the SSTV subcarrier (two signals, Cop McDonald format). There are a few software versions for PCs and 'phones, but maybe they don't cater for this original format. No reason why someone couldn't develop one...though not me!! I've no idea where to start...

I've just reviewed the original hardware and software, both need some 'tidying-up' here and there, but the majority is already done. Perhaps a bit of updating too, it was some years ago...

Your thoughts?

Steve A.
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Re: SSTV picture/file generation.

Postby Steve Anderson » Thu Oct 28, 2021 4:55 pm

Further thoughts...I posted an item some time back r.e. Ralph's 'ROMscanner' and an update thereof. I may have mentioned that this in principle could be applied to SSTV as well. I'll have to look at my notes and postings to refresh my mind where I got to on this...

Feedback still welcome...

Steve A.

Ah yes! The 'FotoStor'...part of the reason I've not been so pro-active in recent times is a 'real work' project I've been involved in for almost 18 months. We're in the final documentation stage with completion estimated mid-November. Unless something else comes along I can get going on this...
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Re: SSTV picture/file generation.

Postby kd2bd » Fri Oct 29, 2021 6:35 am

I created some SSTV image generation software back in 2003 for testing SSTV demodulation circuits. Written in 'C' and utilizing the Advanced Linux Sound Architecture (ALSA) framework, it has grown over time to provide the following functions:

Available Modes:
-t: Tone Generation (Frequency (Hz) Duration (secs))
-m1: Martin 1 SSTV Color (320x256)
-m2: Martin 2 SSTV Color (320x256)
-s1: Scottie 1 SSTV Color (320x256)
-s2: Scottie 2 SSTV Color (320x256)
-sdx: Scottie DX SSTV Color (320x256)
-bw7: 7 Second (50 Hz line) SSTV Monochrome (128x128)
-bw8: 8 Second (60 Hz line) SSTV Monochrome (128x128)
-uo9: OSCAR 9 CCD Monochrome (256x256)
-same: Specific Area Message Encoder
-bw34: 34 Second SSTV Monochrome (256x256)
-rgb8: 3x 8 Second Frame Sequential SSTV Color (128x128)
-fax480: FAX 480 SSTV Monochrome (512x480)
-sc2180: Wrasse SC2-180 SSTV Color (320x256)

Other Options:
-n: Repeat Transmission 'n' Times
-r: Audio Sampling Rate (Hz)
-o: Output File (.wav)
-grey: Transmit bottom greyscale (bw7, bw8, bw34, rgb8 modes only)
-novis: Transmit no VIS Header Code in rgb8 mode

The program works from the Linux or Unix command line with either monochrome Portable GreyMap (PGM) or color Portable PixMap (PPM) images, and either generates SSTV audio through the system soundcard, or writes its output to a .wav file.

For generating 128-line SSTV video, 256x256 images work best, and the program will shrink or expand images to fit the 256x256 pixel layout. It correctly generates monochrome SSTV video from color PPM images.

I often use XPaint software for a lot of things, including the editing and generation of SSTV images. I will sometimes create a blank 256x256 image canvas in XPaint, load up a JPG image into a separate canvas, copy and paste a portion of the JPG to fill the 256x256 image canvas, and then save the canvas as a PPM or PGM image file.

Plus, there's the GIMP and ImageMagick for image display, format conversion, and manipulation.

I offer this as "food for thought" as there probably aren't very many Linux users here. However, the numbers often jump every time Microsoft releases a new version of Windows. :lol:

73 de John, KD2BD
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Re: SSTV picture/file generation.

Postby Steve Anderson » Fri Oct 29, 2021 6:27 pm

kd2bd wrote:..there probably aren't very many Linux users here.
73 de John, KD2BD

Generally true anywhere. Though I used Linux (Ubuntu) up until 2016 when I had to upgrade the PC to Win 10 to run Autocad 2016. That project is long finished, but I've simply continued on with Win10...

Quite an impressive list of achievements there, some modes I've not even heard of! For me it's the Cop McDonald standard(s) and maybe, maybe I may concede trying PD120 one day, maybe...only 'cos the ISS uses it...though I may be interested in the bw34 mode too...even though no-one probably uses it today...

Getting hold of all the 'official' specifications for those various modes must have required quite extensive detective work and patience!

Steve A.

Postscript: John, if you have the actual figures for the bw34 mode, I'd like to have a look at them...
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Re: SSTV picture/file generation.

Postby kd2bd » Sat Oct 30, 2021 3:45 am

Hi Steve.

Yes, finding the specifications of many of the modern SSTV color modes was difficult and time consuming. In some cases, I looked for clues in the source code of QSSTV, an Open-Source SSTV application.

The UO9 mode produces the image format used by the OSCAR-9 satellite to transmit 256x256 monochrome images by way of synchronous AFSK at 1200 bps. I've done some work with this image format in the past.

The Specific Area Message Encoder isn't an image format, but a mode that transmits text in the form of synchronous AFSK at 520.8333 bps. Again, this was included as an aid for some work I had been doing with this data format.

The 34 second SSTV mode consists of 256 lines sent at a 7.5 Hz (15 Hz / 2 ) line rate with standard 5 ms horizontal and 30 ms vertical sync pulses. The Microcraft Videoscan 1000 and I believe the Robot 300 storage tube-based scan converter supported this mode. I have tested this mode with my TriplePIC scan converter and the results were amazing. You put in a 256x256 image and get an exact replica displayed on the monitor, without any resolution loss due to bandwidth or FM encoding/decoding restrictions.

The "rgb8" frame sequential color mode was man's first attempt at sending color SSTV images. I had a few transmissions on tape from around 1981 that I managed to decode last summer using my scan converter and some additional software to render each frame in its appropriate color. 39 years later, they finally got to see the light of day:


youtu.be/yqHcZzvD9Bs


youtu.be/1q66zazyJLU

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Re: SSTV picture/file generation.

Postby Steve Anderson » Sat Oct 30, 2021 11:06 am

Thanks for the info John. Both the bw34 and the rgb8 modes interest me, certainly the bw34 mode would be a fairly simple software update to the bw7/bw8 modes...with an increase of RAM size. Though my MkI version up-converter had plenty of RAM to spare. The stalled Mk5 also, though significant hardware updates would be required for colour modes for both...

But they're going to have to go on the 'back burner' for a while as I have plenty on my plate already...

I may be able to get a surplus 625/50 monitor from my wife's TV station (possibly two) which will restore my ability to display that standard...the old JVC 21" CRT TV 'expired' a while ago, there is a TV repair shop locally, not sure if it would be worth it...

Later again: A few stabs at the calculator confirms that the bw34 mode is viable and compatible with the 1200/1500/2300Hz original SSTV mode, so the same modulators/demodulators/transmission/reception modes can be used...ideal...video baseband bandwidth required, basically the same at 1kHz...

As it's so similar to the 7/8 second modes I'll include it in future projects, RAM size is not a problem anymore...though speed needs careful attention...including whether serial or parallel...serial preferably...if I can 'drop back' to 625/50 rather than VGA I don't see an issue...but need to consider interlacing...a quick muse, no problem...

Steve A.
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Re: SSTV picture/file generation.

Postby Steve Anderson » Tue Nov 02, 2021 8:08 pm

I picked up the two 12" monochrome Ikigami Camera Preview monitors this morning, complete with manuals, which quote a horizontal resolution of 500 lines horizontal. Ideal, and with that resolution of course they are monochrome and the usual chroma subcarrier filter can be switch in or out as desired. Most CCUs (Camera Control Units) have dual outputs YUV (the Y only used for the monochrome preview monitors, with the chroma filter switched out), RGB for Chroma-Keying, as well as the usual 270Mb/s digital SDI output for the Vision Mixer etc...though these days Chroma-Keying is usually done within the vision mixer...

They both work OK and look like they've been hardly used, high hopes...

I was also able to blag an Otari MX-55 2-track 10.5" open-recorder from the same source not so long ago, though I suspect all (if any) rubber belts, pinch rollers and the like are going to need replacing. Possibly the record and replay heads also, and they won't be cheap...a guess? Maybe US$300 each...

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Re: SSTV picture/file generation.

Postby Klaas Robers » Tue Nov 02, 2021 9:54 pm

Never change things before you experienced that they are defective. Video recording / play back heads can have a long life, as there is a very thin layer of air hetween the head and the tape when they are working. Only very rough tape can go through this air layer and will abrase the head.

I have still monochrome (black and white) monitors from the black and white era. They have generally two interconnected BNC input connectors, one for the video input signal and the second one for a 75 ohm terminator resistor. Or you can go from there to a second monitor, which is properly terminated.

When I started at Philips Research in 1971 we had an RGB colour TV studio. Tens of miles of cable were lying under the floor, because every connection needed 4 cables, R, G, B and Sync. The cables had of course equal lengths and were always kept together. That was the time of my Avatar Lady with Roses.
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Re: SSTV picture/file generation.

Postby Steve Anderson » Wed Nov 03, 2021 12:29 pm

Klaas Robers wrote:Never change things before you experienced that they are defective. Video recording / play back heads...

In this case it's an audio recorder, so there isn't that protective air-gap between heads and tape, so wear over time is inevitable. I haven't had a chance to check the machine over as it's still in storage at my brother-in-law's place. I should go and pick it up, one day...

Magnetic tape has been part of my life since I can remember. My father worked for Zonal, a magnetic tape manufacturer based in Redhill, Surrey, UK. They were chosen to supply the BBC with audio tape over the likes of Ampex, BASF, Agfa, Scotch, EMI and a few others. Though they never could quite get their videotape formulation quite right.

It's a similar story with his father (my grandfather) who worked for Ilford, the photographic film manufacturer. Their monochrome films were (and still are) very well respected, but they never managed to get their colour emulsions quite right. Kodak/Eastman winning that war.

Steve A.

Brochure photo of the Otari Mx-55....

Mx-55.jpg
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Re: SSTV picture/file generation.

Postby Klaas Robers » Thu Nov 04, 2021 6:03 pm

Wow, impressive. Does it run at 38 cm/sec. or only at 76 cm/sec? And do you have enough of those large professional reels?
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Re: SSTV picture/file generation.

Postby Steve Anderson » Thu Nov 04, 2021 9:15 pm

It's a 38 cm/s (15"/s) and a 19 cm/s (7.5"/s) half-track machine only (the full width of the tape is used on a stereo single pass). Some were made with 9.5 cm/s (3.75"/s) as well, but not this one. It's all balanced audio (XLR) I/O. Yes I have plenty of good reels of unused tape, all I hope is that all I need to do is re-bias it for the tape I have...I have the necessary head demagnetiser, edit block and a piles of single-sided razors for editing too, and the splicing tape, plus all the other audio stuff to get it right...

The best editing machine for radio and news was the Revox B77 in it's cut-down version. No controls except the tape transport, no meters, no gain controls, nothing. It was a one-to-one recording machine. You put 0dbm in, you got 0dbm out, that was it. Without all that usual crap in the way you had a nice editing area to work in...Telefunken did a similar machine too, I don't recall its model number...it was built for warfare, and with most DJs and Journalists it needed to be, they are animals...

These days it's all done electronically, but they still need to withstand the environments these people may be asked to work in...

In the old days the reporters machine was a Uher open reel recorder, later replaced with a Marantz cassette, there is a museum somewhere in London where you can see these machines with horrendous damage inflicted in the course of the reporting, machines literally folded in half as a tank drove over it, bullet holes in others...what ever happened to the poor(?) reporter? And also their supporting crew...particularly with television...

Steve A.
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