Read a VGA signal, handle it and use with a led matrix.

This is a non-trivial project, but feasible - probably not just with a small PIC or arduino though. There is a book that will help. It's called Digital Video Electronics by Andrei Cernasov. It's quite old (and just averagely useful, not the best, but is practical-oriented), but some of the information is quite relevant. You'll need a fair bit of electronics knowledge (which you may already have).

You could take a video and resize to 100x100 to see if you'd be satisfied with the results. Also, the cost/effort seems high for little benefit with such a low resolution.

EDIT: Also see this URL for valuable information.

Thank you for your answer, I will try to find that book, but what you mean "not just with a small PIC or arduino" ? It seems that in the link they are using some sort of programmable board similar to arduino, am I wrong? (unfortunately at the moment I am unable to read all the link)

From what I briefly saw, they are using an ARM processor - and using DMA capability. The AVR based arduino devices won't be sufficient. The higher-end ones might be.

I'm looking the link you gave me. It's absolutely interesting and maybe (if I understood what a OctoWS2811 do) is also daisychain capable, am I right? Using that, maybe changing the strips and creating a board ad hoc, I can imagine a big step forward for my project...

Great, glad it helps. Yes, you can daisy-chain, those particular LEDs are extremely popular, many interesting projects using these.

I was reading the link you gave me this afternoon and I noticed that all the system is based on a NeoPixel RGB led Strip that uses a WS2811 chip as driver for each led. One of the first thing is that create a big led wall with commercial leds product is far more expensive that buy a brand new one, so I was wondering if is there any place where to buy big stock of RGB leds and what driver I should use, in first place I thought I should address each led directly from the main board, using something like a cascade of decade counter to activate each led, that is using 3 out for R,G and B, one for HSync and one for the VSync.

Maybe this can lead to persistence issues? or maybe I need a too fast board?

The ws2811 (as specified in the datasheet) holds the data until a reset, is then necessary to have a single IC for each led? We are talking easily of more than 200.000 ICs! in case of a 600x400 screen. Is there any similar IC that can handle more Led at once? or even is there anything similar to the ws2811, because I can't find any site where buy them not to a final-user price

The integrated circuit is inside each LED for the WS2812B devices. It is built-in. It's possible to buy these devices individually (not soldered in strips) too, in reels of hundreds or thousands, usually from China or Hong Kong (I don't have a source, I just obtained a small quantity from ebay but not used them so far).

I was lookin in the net, but the only site that I found has a 100 pieces pack at 13$, for a 4x2,25 m wall (90000 led) is about 11.000$! I need absolutely to find a 10 time cheaper leds. Any Idea?

Of course I can also win the lottery, but is like cheating

By the way, reading further the link, seems like the OctoWS2811 board don't concerne any kind of ethernet transmission, it only uses the cat6 cable to distribute 8 data signals. No Ethernet, no daisy chain... a step back for me, but indeed I have much more ideas.

A factor of 10 cheaper (1.3 cent per LED) is unlikely to be possible. Even plain RGB LEDs (with no in-built controller) cost 31 cent each from Newark in quantities of 10000.

90 000 LEDs each at 50mA will draw 4500 amps max at 5V, which is 22kW of power. This is not practical.

there must be a solution, how can a commercial ledwall (more than 100.000 certainly) be powered then? Maybe I need smaller leds, not Hi lux...