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Dynamic_Computing

Posted Mon Sep 17, 2018 9:04 am

I am working on a review / video of the Digital Creations DCTV. I have two of them and they work OK, but they clearly want to use an old 1084 style RGB monitor, as the actual DCTV image does not show up properly on my LCD display connected to my RGB port. Now I do own a nice 1080 monitor, but the previous owner decided to rip out the 23 pin RGB connector for some insane reason...

The image does work OK on the Composite Out, and I can convert them to 24 bit IFF images without a problem, but...

* Has anyone had any luck getting the images to display on a modern monitor
* Does anyone use these today for image capturing, and if so can you send me some cool samples to show on my review
* Any really cool tips/tricks that this thing can do that are not covered in the manual?
* Any preferred settings, either in the software on on your camera to get the best image?

It is really odd how little DCTV info is available out there.

Dynamic_Computing

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santidarkg

Posted Thu Sep 20, 2018 10:12 am

Dynamic_Computing wrote:I am working on a review / video of the Digital Creations DCTV. I have two of them and they work OK, but they clearly want to use an old 1084 style RGB monitor, as the actual DCTV image does not show up properly on my LCD display connected to my RGB port. Now I do own a nice 1080 monitor, but the previous owner decided to rip out the 23 pin RGB connector for some insane reason...

The image does work OK on the Composite Out, and I can convert them to 24 bit IFF images without a problem, but...

* Has anyone had any luck getting the images to display on a modern monitor
* Does anyone use these today for image capturing, and if so can you send me some cool samples to show on my review
* Any really cool tips/tricks that this thing can do that are not covered in the manual?
* Any preferred settings, either in the software on on your camera to get the best image?

It is really odd how little DCTV info is available out there.

Dynamic_Computing
Yes, DCTV was an awesome device (an still it is). It can display around 6 million of colors, animation in 24 bits in real time if you Amiga has enough memory, capture a still frame from a video source, etc. The DCTV pain is very cool too. It was my first addon and my 3d world started here with Lightwave and DCTV. It was really great.

* No. I have been trying to take the video output on my Dell 24 inch (old monitor). It has video input, components, etc. I can see my A1200 video but not the video output from my DCTV, just a black screen. Not idea why is doing this. I need to check my Dell 30 inch and see if there is doing the same thing. Maybe DCTV needs a sync or something coming from a CRT monitor..... not idea right now. If you find a way to display the video output, let me know, I am interested too.

* Like I said. DCTV was a beast. Can you imagine back in 1990 having millions of colors on the screen and making animations in real time ? It was insane. You can use Deluxe Paint, LIghtwave, ClariSSA, ADPro..... it was very well integrated with a lot of applications.

* Settings....... nothing that you can do here to improve the video quality to capture a screenshot. It is a regular video VHS and thats it. Back then, it was great.

Maybe somebody else has been using a DCTV and could comment more things here :)

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FerociousAmiga

Posted Sun Jun 06, 2021 10:46 pm

Few year old thread but did you ever make the video?

Did find this information on a comment on another site.

https://retrocomputing.stackexchange.co ... -dctv-work

After some research, I found the hardware engineer that built the DCTV and we exchanged some messages where he explained the system.

This is the unedited text:

Wow, it has been a long time... I didn't really remember! Luckily I still have all the lab books and design notes from those days filed away. We used a technique that encoded the data on two consecutive lines in the Amiga frame buffer in a way that we could reconstruct a composite video signal when run through some processing and combined with data from the previous line (delayed through a line memory). I know that is pretty ambiguous, but it is a general description. I will describe in more detail below, but it assumes some familiarity with NTSC composite video signals.

In more detail: Amiga had a frame buffer mode that displayed 736x483 pixels, but only 4-bits per pixel (16 colors). We used that mode, but re-interpreted the data. We combined alternate pixels so that we had 8-bits per pixel at half the rate. Even (I think) lines stored data as Y + (R-Y), Y - (R-Y), etc. [Luma +/- red color difference value, alternating] at a 7.159MHz sample rate. Odd lines stored data as Y + (B-Y), Y - (B-Y), etc. [Luma +/- blue color difference value, alternating], logically shifted by half a 7.159MHz sample. So every line would contain every other raw sample for an NTSC composite video signal. In order to reconstruct the missing data, it would generate the Y component by averaging the values left and right of the missing sample, and the chroma component by subtracting the two adjacent samples from the previous line. The final value was created by adding these values together. The resultant data stream was at 14.318MHz and contained Y+(B-Y), Y+(R-Y), Y-(B-Y), Y-(R-Y), etc. When converted to analog and added sync and so on the resulting signal was a full color composite signal that looked surprisingly good.

So it was really a way to get full color out of the Amiga frame buffer by applying some signal processing techniques to trade off spatial resolution for increased colors. Instead of a frame of 736x483 pixels of 16 colors, we got an effective resolution of about 368x483 pixels of full NTSC type color. Chroma resolution was less (as with any composite NTSC type signal), including somewhat less resolution vertically. But it looked pretty good by 1990 standards! We found that we could even stream data off a fast (for the time) hard drive in real time, and used to demo by playing back scenes from "Back to the Future" at trade shows. Fun times.

Actually we may have used the 704x483 graphics mode... I got he 736 number from Wikipedia, but I am not sure it is correct. 704 sounds more right.


Then me asking a bit more:

You have cleared a mystery that was popping back in my mind now and then! It is true that for the time, the output was very good! so you could probably fit the decoding logic in a cpld?

And he replied:

The decoding logic fit in a 3000 series Xilinx FPGA. The line memory was external, along with the D to A converter and a few other things like a PLL for the pixel clock. I think the final product had an A to D converter for grabbing images from an external video source as well...
I will let him know about this thread just in case there are more questions, to see if he wants to participate.






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