LEDs and taking video of them...

Any keen photographers out there who understand cameras really well? I've been working on my LED project (abstract art within a frame) and have got to the point where I'd like to take some video of it.

This thing is bright... 180cm of 60 LEDs per 10 cm RGB LED strip, split into three sections, for 324 LEDs in all (if you're counting the R, G and B distinctly).

My little Canon Ixus 65 (yes, I know it's quite old these days) just gives me a load of white if I try to video it... well, slight exaggeration, but mostly white. I've tried changing the ISO to the highest and lowest it offers (not sure of the actual levels, it's a slider bar) and I've tried alterating AWB to "Custom" and evaluated the white balance...

I've checked back the results after each test and - to be honest - I really couldn't tell much difference, I can certainly say that none looked like what my eyes were seeing.

I guess cameras are just not like the human eye, but I'd be curious if anyone had any hints and tips as to how you might go taking video of bright LEDs with something modest like my camera.

P.S. - I've been doing it in a dark room, I really should add that, which might well be making my problem worse (probably is?)... I could try it in a daylit lit room tomorrow.

1. Try it in a better-lit place. Main problem is you have waaaaaay too much contrast. The camera's sensor has a limited dynamic range, and you're exceeding it.

2. Play with the exposure (in other words, don't let the camera set the exposure). Don't know what control you have over this (aperture & shutter speed), but if you do, try underexposing it.

It is the contrast that is messing you up. Consumer image sensors don't like any big contrasts between the brightest and the darkest part of the screen.

Your only hope is is to seriously under-expose compared to what the automatic exposure setting asks for. That way the LEDs should be the right colour and everything else will be black. You could try sports mode in the video if you can't control the exposure directly.

White balance won't help. That will get subtle shades, like skin, to look right if the lighting is a bit coloured.

The ISO setting won't help because that still leaves the auto exposure working.

Another option is to turn down the current to the LEDs. Besides the high contrast, what you're taking a picture of is not a typical subject -- and the metering algorithms for the cameras have been fine-tuned for the typical subjects (say, people standing for a portrait or a landscape photo). You might also want to experiment with a neutral density filter. But I think the main problem is dynamic range, as carbonzit has already stated -- the typical camera sensors have less dynamic range than the human eye.

I agree with those who mention the camera's metering and that camera does not offer metering options. I like CB's suggestion of trying in a bright well lit area with uniform lighting.

Ron

squishy36 said:

Another option is to turn down the current to the LEDs.

Click to expand...

This is the best idea yet in this thread. Why didn't I think of that? Simple, and should solve the problem (or at least greatly help).

If you still have problems with it being too bright in a well lit room try using a neutral lens filter. In a pinch a cheap pair of gray sunglasses will work.

Thanks for the responses.

OK, firstly I'm going to give it a go in the daylight (still inside the house, of course) tomorrow.

I'm currently running the artwork connected from my bench PSU at 12v with a MAX667 dropping to 5v for my PIC... it obviously has the option of using a proper DC connector, but I've been tinkering with it today - I wonder if I could run the LED part at, say, 9v or lower to drop the brightness of the LED strips. It could work just for this video task I want to do, with everything else being exactly the same.

To reduce their brightness, remember you need to reduce the current through the LEDs, not the voltage. Reducing the voltage input to a voltage regulator ain't gonna do it.

I can assure you that reducing the voltage to 9v reduces the brightness of the RGB LED strips. I only said the voltage regulator was dropping to 5v for the PIC part of the circuit... I have ULN2003ANs allowing 12v to go to the LED strips. When I power the whole thing at 9v, the LEDs do get dimmer and the PIC still gets his 5v.

Whether it's dim enough to help with the videoing, I'm not sure.

Well, this is about as good as I can get... it still looks miles better in real life, and - of course - it would be a lot brighter. Anyway, this is the result of my first PCB that I was talking about in another thread... all very compact, neat and tidy, and will hang on a wall nicely.


PIC 16F1825, 32MHz.
MAX667.
2 x ULN2003AN.
180cm of RGB LED strip.
Own PCB.
JAL.

Hi,

That's not too bad. What is this thing going to be used for?
And where did you get the LED strips?

Used for?

It's art. It's non-motivated as opposed to motivated in nature, I guess. I don't expect it to bring about political change or communicate anything deep and meaningful. Maybe it will have the purpose of relaxing someone once it is hung on a wall... especially if I slow things down a bit and make it less... well, hectic. There are some very soothing colours in there that don't come across very well on the video. I think I will create a new effect programme that does very subtle fades from one soothing pastel shade to another and then it can be 'randomly' selected.

I think I am actually going to give it to one of my friends for their birthday. Much better than something like yet another book from Amazon.

I got 5m of the RGB LED strip from brightlightz.co.uk, but I've used other sources too.

P.S. - this is the IP65 stuff, waterproof (although I have no need of that) with the plastic covering, I think that adds a nice effect to the colours.

Hi again,

Yes it looks much nicer than some of the other LED strips i've seen. I'll have to try to find some.

Oh did you put your own plastic over them then? Couldnt find the ones you talk about on brightlightz.


BTW, my birthday is coming soon...he he just kidding.

Looks good enough from the video, but the colour and light appear to have absolutely no relation to each other. If the music isn't intended to be part of then that's fine. But if you want this on a wall for long term viewing you'll want to tone things down a bit, I'd rip something like that off the wall of my house inside 5 minutes if I was in the same room, WAY too distracting, you'd have to do VERY slow (like 20-30 second) color/brightness changes for it to look decent as an ambient piece of art. If you make the changes slow enough like minutes or hours it will have more impact as you'll occasionally think to yourself "wasn't that a different color a few minutes ago?"

That's programme demo mode in the video that you're seeing.

When it goes on the wall, the selection of the effect programmes will be weighted... strobe effect (very off-putting) will have the smallest chance of being selected (that being very, very small), solid colour change mode will have the highest. Slow fade will be next highest. Things like beat and RGB fast fade will only happen once in a blue moon. Also, it will not flash white between programme changes, it's just doing that right now so it shouts "I'm changing programme" at me while I'm observing it for long periods of time for quality control. I'm going to add a nice pulse... like a breathing effect... selecting colours and then dropping their R, G, B levels by 150 over half a second, then back up... giving a nice resonate effect.

Any more programme ideas welcome.

A flicker effect would be nice, like that of a candle, all you have to do is ad a low frequency random number to the output. Just a hint for the fading, linear fading is very unappealing to the human eye, if you create a sine table in memory and convert the linear value to a sine approximation the fading effect will be dramatically more pleasing to the human eye.

Since this is art and obviously this is something that should be looked at how about adding a small piezo speaker? Not to produce music or noise, but mid/low frequency ticks VERY infrequently when you want someone to look at it cause it'll be doing something dramatic. Loud ticks with extremely short duration spread apart over long periods of time will get any human being curious about what's making the noise.

Overall the video came out pretty good. As to the concept, yes it is art. However, can it be synced to Black Sabbath playing at 78 speed?

Seriously, not bad at all.

Ron

On a personal note, 7 bits is passsable 8bits is 'okay' for passing fading and glow effects, but as someone who has a keen eye for the appearance of stepping effects in PWM'd LED drivers I'm going to recommend adjusting your software/hardware so that you get at least 10bits of dimming control, and ideally it should be a DC current controlled source not PWM'd. People seriously underestimate the ability of the human eye and more importantly the brain to catch harmonic or 'unnatural' seeming effects. For more subtle effects like shallow dimming effects at low frequency this is especially important, 12bits or higher if you can swing it will really set the display apart from just being a piece of junk thrown together to something awe inspiring, the devil is in the details =)

I'm a bit stuck on adding other things to it, guys... like a buzzer or some kind of music sync.. I had been thinking about both these things to be honest, but I've gone and designed my first PCB around this and, well, that's it for the time being - it's kinda set it stone, apart from the software side. Neatness (to some degree at least) is important to me and this was my first departure from veroboard... the back side of this picture pleases me almost as much as the front.

The fact that it's cost me a fair whack to get this far... £55 for 5 of the frames, £50 for the 3mm perspex sheets, £50 for 5 metres of RGB LED strip, £4 for L-shaped edging to hold the LED strips, about £60 for my PCBs, few more Quid for my switches and DC connectors... makes me understand that no hobby is 'cheap'. I couldn't scavenge these parts for instance. I do have the capacity to build more of these, though... and each one can be unique.

I'll have a think about the non-linear fading... I've not considered that before, all I do here is increment or decrement by 1... all I've cared about to this point is having no flicker when 8-bit PWM'ing 9 LEDs (as you may have seen from my other threads).