Does anyone know of a box I can stick between a CCD camera and a screen to allow adjustment of the video's histogram? I essentially need a box to perform histogram equalization or something that allows me to manually adjust the histogram of the video.
In other words, I have a video signal that looks like the image on the left and I need a box to transform it into the image on the right, in real-time
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That is what's known as a "Proc Amp" (for processing amplifier). Their features are usually/often included on full-featured TBC's (some also including Noise Reduction, or DNR), though you can get them as standalones.
They usually have (at least) 4 controls:
- Setup (aka Pedestal aka Contrast aka Black Level, etc) - adjusts the lower bounds of the luminance scale (greyscale)
- Gain (aka Luma aka Brightness aka White Level, etc) - adjusts the upper bounds of the luminance scale
- Hue (aka Tint aka Phase, etc) - adjusts the correct orientation of the chrominance points
- Saturation (aka Chroma aka Color, etc) - adjusts the absolute value upper bound of the chrominance scale
More/especially helpful when used in conjunction with a waveform monitor (#1,2,4) & vectorscope (#3,4). Most helpful when you have associated colorbars to use as a reference, but you can eyeball it if you have experience with how those should look.
Thanks for all the information Scott. Very helpful.
We're dealing with a monochrome camera, so setup and gain may be the only controls of interest. Are you aware of any brands that sell stripped down versions of these amps? The camera has a 570TVL resolution and a BNC connector output. A simple box with one BNC input, one BNC output, and control knobs for setup and gain sounds like it would be perfect.
I see SignVideo used to make a Proc Amp that looks ideal: http://www.signvideo.com/pdfs/Proc%20Amp%20manual.pdf
Unfortunately they don't seem to make it anymore... bummer.
Last edited by oknowgo; 17th Aug 2012 at 14:45.
But I don't know if a proc amp will do exactly what you want. I suspect you're going to need a gamma adjustment. Or some other non-linear transform.
That may be true. I'm not really sure. If I look at a histogram of a typical frame of video it looks like this:
The distribution of pixel levels is narrow and low, so just adjusting the lower and upper bounds may be sufficient, don't you think? If I wanted to do some kind of gamma adjustment is there equipment to do that in real-time?
Do any of these companies actually still sell proc amps or do you have to find them secondhand? SignVideo and EliteVideo's websites are almost unusable. I know SignVideo no longer sells them. I can't tell if EliteVideo does or not because I can't actually find where to buy them on their website.
Last edited by oknowgo; 17th Aug 2012 at 15:31.
ProcAmps that ONLY did Luma would have been sold around the time when Black & White cameras were still common. They haven't been for a long time (excepting science/security sectors), so you'll have to settle for a full color ProAmp (unless you found an old '60s-'70s one on ebay/craigslist).
In those cases, you would need to remember to TURN DOWN the Chroma level to 0 (even if it should already be zero), as chroma noise can "leak in" to the signal from the box.
jagabo is correct, however. You will likely need gamma, and other, adjustments. ProcAmps rarely (never?) have controls for that. But if the levels are at least within range (having done the adjustments in the ProcAmp that you CAN do), you could always do a gamma adjustment after capturing, by using Virtualdub, AVISynth, etc.
However, if your "in realtime" requirement is a dealbreaker, you may be out of luck getting it just right.
Depends on what you need...
Do you need your histogram waveform centered?
or do you need it expanded?
or do you need it equalized?
The 1st would be done adjusting mainly just a brightness/level control, the middle one done by adjusting the setup & level controls, but the 3rd one would be done by adjusting a gamma control as well as the other 2 controls.
Given that histogram I think you might be ok with just a proc amp. Try opening one of your videos in VirtualDub and use the Levels filter without adjusting the Gamma control (the middle slider). If you can get what you want with that then a proc amp will probably work for you. But often with linear adjustments like that, if you adjust the gain enough to bring out details in the dark areas, the bright areas get blown out.
Do you have a short sample video you can upload?
Sure here is a short segment of video: http://dl.dropbox.com/u/26841375/cells.mov
We don't actually record video, we just watch this on a screen as we work. That is why we need these enhancements to be done in real-time.
We're trying to improve visibility of cells.
Last edited by oknowgo; 17th Aug 2012 at 16:58.
I've concluded the same. Thank you both for your help. Now to find a place that still sells these things...
I agree. Elite & Vidcraft, have used both before successfully...
Another possibility if you can use a computer is to use a capture card that has proc amp controls that let you watch the video on the monitor.
Sorry to resurrect this topic. Can someone point me to a shop that actually sells these standalone proc amps (preferably rack mountable)?
I want to buy them new and, for the life of me, I can't find anyone actually selling them outside of ebay! Not even EliteVideo themselves seems to sell their own product??
I do see B&H still sells Hotronic brand proc amps: http://www.bhphotovideo.com/c/product/378724-REG/Hotronic_PROC_AMP_RM_PROCAMPRM_Video_Processor.html . Anyone have any experience with these?
Last edited by oknowgo; 22nd Aug 2012 at 15:02.
Neither Elite nor SignVideo manufactures proc amps anymore -- you just missed the boat, SV just discontinued there proc amps in the last month or so. You'll have to look into the used market -- the SV proc amps are very durable and well made.
Problem is, with most cameras being digital now, you either forgoe in-line proc amp control, or add a dedicated a-to-d and d-to-a process (with slight quality loss and more cost) or get a proc amp that works for either analog OR digital (for even more cost).