NBTV/SSTV-625 Up Converter MkIII

[Andrew Davie]

What I should perhaps also think about is some form of SSTV generator that turns a standard monochrome BMP or TIFF file into the 8-second format. I've already done it to generate the signal/pictures for the previous up-converters, but it could do with a lot of simplification and rationalising. More later...

Steve A.

I'd suggest using/learning Python. It's cross-platform, efficient, and extremely easy to program. Image format support is easy.
I'll do it for you if you're daunted.

[acl]

Hi there all.

Progress looking good Steve. I was impressed with the quality of Andrews boards. At leaset this will allow construction to be simple, consistant and may attract others into the realms of classic SSTV. Keep up the good work.

Chris Lewis

[Steve Anderson]

...and may attract others into the realms of classic SSTV. Chris Lewis

I've sent Paul Turner, G4IJE an e-mail (classicsstv.com which I recently linked to) outlining where I am with this as well as a few screen-shots of the MkI version. I'll keep you updated...

This will now continue in a new thread, "NBTV/SSTV Up Converter MkIV.

Steve A.

[Steve Anderson]

...I'll do it for you if you're daunted.

I may take you up on that offer! But first I need to get this MkIV converter going...

Previously how I created the SSTV audio files was:-

1) Select suitable image, say a jpg.
2) Crop it to a square 256x256 pixel format.
3) Convert to 8-bit monochrome.
4) Adjust black/white levels (contrast) to suit.
5) Save as an uncompressed TIFF file.

I used the free "Irfanview" software do to the above.

The file is sent to an external piece of hardware that strips off the header info and leaves just the uncompressed picture data. Always the same size, exactly 65,536 bytes. This is converted to baseband SSTV which then feeds a simple DDS SSTV modulator. The file continually loops until another picture is loaded. Only 128 of the 256 lines were converted, i.e. every other line was skipped.

In other words...it was somewhat tedious!

Steve A.

[Andrew Davie]

That's about 5 lines of Python code

[Steve Anderson]

That's about 5 lines of Python code

Amazing! It does seem rather silly to do a hardware based version in that case.

There is an online page which I have not tried yet:-

https://www.vr2woa.com/sstv/

But for the Robot 8s mode it specifies a minimum input file dimensions being 160x120, is that pixels/lines or lines/pixels? With those numbers it implies a 4:3 aspect ratio whereas Robot 8s was usually (always?) 1:1, square. There's only one way to find out I guess...

And what's the line rate? 15Hz(60Hz countries) or 16.7Hz(50Hz countries)? More recent SSTV modes don't have this regional variation.

As with anything on the 'net, the site may also vanish at any time...

Steve A.

[Andrew Davie]

In my world (which involved a fair bit of image manipulation/handling), dimensions are always width x depth.

[Steve Anderson]

In my world (which involved a fair bit of image manipulation/handling), dimensions are always width x depth.

Yes, that would make sense, but, but, but...

I'll give that on-line SSTV generator a try soon...

Steve A.

[acl]

I recently was working on an EPROM based signal generator for NBTV. Thorght you may be interested in some of the 'jumping through hoops' as many of the editing programs lacked all features.

Stay Safe

Chris Lewis

[smeezekitty]

What I should perhaps also think about is some form of SSTV generator that turns a standard monochrome BMP or TIFF file into the 8-second format. I've already done it to generate the signal/pictures for the previous up-converters, but it could do with a lot of simplification and rationalising. More later...

Steve A.

I'd suggest using/learning Python. It's cross-platform, efficient, and extremely easy to program. Image format support is easy.
I'll do it for you if you're daunted.

Python - efficient?

Good one...

It definitely has its uses but performance is lacking to say the least. It is the most overhyped programming language in existence.

But in any case, there are image libraries available for every major programming language so take your pick.

[Andrew Davie]

Python - efficient?

Good one...

It definitely has its uses but performance is lacking to say the least. It is the most overhyped programming language in existence.

But in any case, there are image libraries available for every major programming language so take your pick.

Horses for courses. I wouldn't write anything real-time in Python, but in terms of efficiency programming and strong and easy-to-use data structures leading to concise and easy to read/maintain code, I'd choose Python every time.