IR Cut Filters - please help a quasi newbie

eggzlot · Jul 20, 2017

Are they necessary? vague question, I know

I am looking at some new exterior cameras. I notice some of the Dahua models have IR's but no IR Cut filter. Is that an issue with daytime images? Dahua get a lot of cred on this forum so I am assuming they compensate somehow?

Can anyone enlighten me because the last time I got a camera it did not have a cut filter and everything was purple so I swapped it out for another model with a cut filter (this was a very small camera for a door station device). I have 2 current external cameras mounted to the house and they have IR cut filters.

So when I see the Dahua without cut filters, I wonder, am I going to get the purple images I had with that 3rd camera I once had without an IR Cut filter.

Dodutils · Jul 20, 2017

Automated IRCut filter permit to get normal colored pictures during daylight and black-white picture at night

Static IR Cut fixed will show no picture at night because IR Light are stopped

No IR Filter at all will produce strange "purple" color cast pictures

If static IR Cut filter is fixed on the CMOS sensor you will never get IR light view at night

if static IR CUt filter is on the lens you can change the lens to a non IR filtered one and will get no picture at night as IR light is filtered

eggzlot · Jul 20, 2017

so that is what I thought - so something like this would produce a purple color image during the day?
DH-IPC-HDBW44A1EN-AS

I noticed 1 model in the Ultra series had a cut filter but most do not. If you get a purpleish image, why so popular? I know that sounds fairly basic but I feel like I am missing something.

Dodutils · Jul 20, 2017

eggzlot said:
so that is what I thought - so something like this would produce a purple color image during the day?
DH-IPC-HDBW44A1EN-AS

I noticed 1 model in the Ultra series had a cut filter but most do not. If you get a purpleish image, why so popular? I know that sounds fairly basic but I feel like I am missing something.

Strange because automated IRCut filters is now the standard and the camera your linked is equiped with automated IRCut filter.

eggzlot · Jul 20, 2017

ah that is what ICR is? Got it, did not know the lingo. When I looked at some other brands (Hik, FLIR, etc) they all write out IR Cut Filter. I didnt know ICR = IR Cut filter...If that is true, you answered my question.

Fastb · Jul 21, 2017

Dodutils said:
Automated IRCut filter permit to get normal colored pictures during daylight and black-white picture at night

Static IR Cut fixed will show no picture at night because IR Light are stopped

No IR Filter at all will produce strange "purple" color cast pictures

Not quite true. I worked at a place that made cams for buses and trains. No "active" IR cut filter was used, maybe due to the heavy vibration environment.
The IR filter on the lens had a "notch", to allow the 940nm IR illumination to pass through, needed when the camera was in b&w night mode. Other IR was blocked. During the day, in color mode, the majority of IR was blocked by the filter, and the small amount in the 940nm range that passed through didn't affect the image (it wasn't "purple-ish). (Firmware may have been involved too. We didn't create the firmware.)
AKA a "passive ir cut".or "soft ircf"

Sure, at night it would be nice to use all IR illumination, not just the 940nm from our illumination leds, but to include other ambient IR. Nevertheless, the cam's nighttime performance was pretty decent.

From Surveillance 101: Low-Light Cameras | SecurityInfoWatch.com
"True day/night delivers clearer images, which dramatically improves low-light operation. This is achieved by using an active IR cut filter mechanism (IRCF), which removes the infrared filter from the imager to give the camera the ability to view near-infrared light. Keep in mind if a camera is “soft day/night,” it will transition to black-and-white video because it does not have a mechanism in place to remove the IRCF. Soft day night functionality does not utilize all visible and available IR light."
ie: "passive" or "static" IR cut filter.

Conclusion: Not having an Active IR Cut Filter doesn't mean you won't get images at night, or that daytime images will be purple-tinted. There are methods that don't need a mechanism to move a filter into and out of the optical path.

I'd be cautious about assuming a vendor would sell a camera suitable for daytime (color) use that would produce a purple-ish image. (as pink/purple as when an IR cut filter is stuck)

Here's a pic where the IR Cut Filter was stuck half-way.
https://ipcamtalk.com/attachments/20000102_232253-bmp.17752/
clipped from from https://ipcamtalk.com/threads/starlight-varifocal-turret-problem.18953/
The nightime pic is interesting too....

Fastb

Dodutils · Jul 21, 2017

Fastb said:
Not quite true. I worked at a place that made cams for buses and trains. No "active" IR cut filter was used, maybe due to the heavy vibration environment. The IR filter on the lens had a "notch", to allow the 940nm IR illumination to pass through

This kind of "soft" IR Filter is not something you find from public vendors, what you'll find are mechanical IR Cut cameras and if no IR Filter you'll get "purple colored" (rare nowadays except very low cost chinese or old models) and I will not bother him talking about difference between 940nm vs 850nm and "special filters", being too technical do not help beginners.

Fastb · Jul 21, 2017

Dodutils,

Solid comments.

Dodutils said:
if no IR Filter you'll get "purple colored" (rare nowadays except very low cost chinese or old models)

Wow, I didn't know that cameras were sold for daytime use with absolutely no IR filter. 'Cuz the image sensor is more sensitive to IR than to visible - the sensor doesn't detect all light wavelengths the same. To use no filter is silly. The sensor is VERY MUCH more sensitive above the visible spectrum. See chart.
Even a compromise filter that blocks everything from ~880nm up would help reduce pinking in daytime images, but would benefit from 880nm IR LEDs.

IR "filter" is typically a coating on glass (mechanicaal IRCF) or the lens (passive IRCF) - so how much cost savings would the cheap chinese cameras see from eliminating a frigging coating?
Interesting....

Dodutils said:
will not bother him talking about difference between 940nm vs 850nm and "special filters", being too technical do not help beginners.

I hear you, and understand.
This forum has many readers. eg: this thread had 80 readers so far. Fenderman moderates (and sometimes calls out BS) with the broad audience in his mind, for the greater good of forum readers. When I researched & wrote my reply for this thread, both the OP and broad audience were in my mind.

Dodutils said:
talking about difference between 940nm vs 850nm

Yeah, I didn't want to go there either, lol. It's been covered in other threads anyway.

Fastb

Fastb · Jul 21, 2017

All,

In hindsight, throwing a graph out there may not have been "user friendly", without an accompanying interpretation.
The optical sensor's output will be twice as high for IR in the 880nm range (for our IR LEDs) as compared to the yellow/green range of visible light.
And your 880nm IR LEDs will produce approx 8 times more image sensor output than light-blue visible light will produce.

That's what I intended the chart to convey.

Forever curious,
Fastb
I drove Mom nuts with "But why?", "Ok Mom, but Why?"

Dodutils · Jul 22, 2017

Fastb said:
Wow, I didn't know that cameras were sold for daytime use with absolutely no IR filter. 'Cuz the image sensor is more sensitive to IR than to visible - the sensor doesn't detect all light wavelengths the same. To use no filter is silly.

Yes and whenever filtered this is why your smartphone can see the IR light emitted by IR TV Remote controllers coz the filter do its job 99% but still catch some ;-)

And remember the old PTZ 640x480 Foscam models (still have one) for example or still today you have some of those TOP-201-like boxed cameras

Fastb said:
IR "filter" is typically a coating on glass (mechanicaal IRCF) or the lens (passive IRCF) - so how much cost savings would the cheap chinese cameras see from eliminating a frigging coating?
Interesting....

Except for the previous example when it says "no room for the mechanical IR Cut" the reason could be to lower the price of the camera and still permit it to be night/day I guess ?

Dodutils · Jul 22, 2017

colmcille said:
Please don't feel you have to dumb things down for anyone.

Sorry I am not english native, could you explain this sentence ?

alastairstevenson · Jul 22, 2017

Dodutils said:
And remember the old PTZ 640x480 Foscam models

That was my first foray into surveillance cameras, quite some years ago.
And the pink grass put me off the idea of further exploration for quite a while.
I still had it on a shelf, but sold it and a few other unused IP cameras on eBay a couple of months back, with the Foscam going at a surprisingly good price.
The buyer comment was 'superb device' which I re-read a couple of times in case my eyes were tricking me.

alastairstevenson · Jul 22, 2017

Google

Fastb · Jul 22, 2017

Being curious, I checked for info on cameras without mechanical IR cut filters.
snipped from Day/night IP cameras: What is an infrared-cut filter?
"There are IP cameras which offer a software day/night mode (sometimes called simple day/night) to improve low-light visibility. These do not feature a switchable filter, instead providing an “always-on” filter for correct colour reproduction in daylight.

At night, the red, green and blue colour signals are added together and treated as white light. The result is a brighter monochrome image in poor lighting. The benefit of these cameras is that they are more cost effective than true day/night cameras."

The cameras I worked with also had IR LEDs for nightime illumination. The "always on" IR filter blocked IR, except for a narrow section of the IR spectrum to allow the IR from the LEDs to pass.
for typical 880nm IR LEDs, the filter woulld block all IR except for 880 nm region. For 880nm, 95% of the IR will pass through. The plot below shows what I mean:

http://opticalfiltershop.com/shop/bandpass-filter/near-infrared-bandpass-filter-850nm-fwhm-100nm/

Fastb

Dodutils · Jul 22, 2017

Fastb said:
The cameras I worked with also had IR LEDs for nightime illumination. The "always on" IR filter blocked IR, except for a narrow section of the IR spectrum to allow the IR from the LEDs to pass.
for typical 880nm IR LEDs, the filter woulld block all IR except for 880 nm region. For 880nm, 95% of the IR will pass through. The plot below shows what I mean:

So this mean if this filter really do its job it may not work well with usual 940nm or 850nm projectors and you'll have to purchase a 880nm projector if you want to turn internal IR ?

IP-MAN · Jul 23, 2017

Dodutils said:
Automated IRCut filter permit to get normal colored pictures during daylight and black-white picture at night

Static IR Cut fixed will show no picture at night because IR Light are stopped

No IR Filter at all will produce strange "purple" color cast pictures

If static IR Cut filter is fixed on the CMOS sensor you will never get IR light view at night

if static IR CUt filter is on the lens you can change the lens to a non IR filtered one and will get no picture at night as IR light is filtered

Hello, i don't want to hijack the thread but i have a question related to this topic,

I have bought a ip cam drived by a Hi3516C and with a OV2710 sensor ( a revotech I706-2)
The specs are 0.01Lux @(F1.2,AGC ON), but in low light scene it's totally dark (even if i set max brightness with onvif settings)

What do this mean ? i had many others ip cam (whitout IR LED) and when it's nighttime they switch to black and white and increased brightness. how is caled this function? this camera see nothing at night unlike the my others camera.

Fastb · Jul 23, 2017

Dodutils said:
So this mean if this filter really do its job it may not work well with usual 940nm or 850nm projectors and you'll have to purchase a 880nm projector if you want to turn internal IR ?

The filter on the camera lens is matched to the LEDs. eg: if 880nm LEDs, then the filter on the lens is chosen, by the camera manufacturer, to pass 880nm. If 940nm LEDs, the lens uses a 940nm notch filter.
If you want to use auxiliary LED illumination, it should use the same frequency.

ip-man,
Welcome to the forum!
I suggest starting your own thread. You'll get more attention and help. Many forum readers may not be reading this thread about IR cut filters.
Regarding the lux specs, they are known to be unreliable. Maybe the camera just sticks for nightime performance. Sorry, I don't have any other ideas.

Fastb

Dodutils · Jul 23, 2017

Fastb said:
The filter on the camera lens is matched to the LEDs. eg: if 880nm LEDs, then the filter on the lens is chosen, by the camera manufacturer, to pass 880nm. If 940nm LEDs, the lens uses a 940nm notch filter. If you want to use auxiliary LED illumination, it should use the same frequency.

That's what I thought, and such 880nm are not as usual than 850nm but it is interesting, I may by one 880nm filter and a projector for such wavelength to see the result or may be i'll find some video example on youtube...

Fastb · Jul 23, 2017

Dodutils,
850 vs 880 may not differ much in how they help illuminate the nightime images.
But 940 illumination may be greatly reduced.
I think @q or @Kawboy12R did a comparison last year on illuminators.

Read some threads here of people who experimented & tested. If you like what you read, give them a "thanks", even tho the threads may be old:
What IR illuminator would be best?
Someone explain IR Illuminators plz + questions
Idea for very bright DIY IR illuminator....

For extra illuminators, consider the beam angle (coverage area), and even-ness of coverage. eg: some have a hot spot in the center.
nayr created a great comparison of auxiliary IR illuminaters:
IR Illuminators Options / Suggestions

Have fun!
Fastb

Dodutils · Jul 24, 2017

Fastb said:
I think @q or @Kawboy12R did a comparison last year on illuminators.

I already have different 850nm IR projectors and I also have one in a box like the 4 x High power LEDs but with a lot of small LEDs that produce a smoother light that avoid to "burn" too clse objetcs/faces but that do no go that far, also I have a few lens for the High power LED projector with different angles.

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IR Cut Filters - please help a quasi newbie

eggzlot

Getting the hang of it

Dodutils

Pulling my weight

eggzlot

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eggzlot

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Fastb

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alastairstevenson

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IP-MAN

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Known around here

Dodutils

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Fastb

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Dodutils

Pulling my weight