Chronos => Software Dev => Topic started by: A.Angelov on July 27, 2017, 11:01:00 AM

Title: Missing (weak) Green colours
Post by: A.Angelov on July 27, 2017, 11:01:00 AM

I have noticed that the camera has hard time capturing properly green objects (it is shifting only the greens toward the yellow colour)
I was wondering if this is an issue with the IR filter that is just in front of the sensor or with the sensor itself.
Do you have any good suggestions to fix it?

Thank you!

PS: The problem more likely is not related to the lighting because I am using high quality CRI (colour rendering index) diodes  and it also happens during sunlight shooting
Title: Re: Missing (weak) Green colours
Post by: tesla500 on July 27, 2017, 11:35:38 AM
Hi A.,

Could you post an image to show the issue? If you have a comparison with an image with proper color that would help as well.

Title: Re: Missing (weak) Green colours
Post by: A.Angelov on July 29, 2017, 05:49:00 AM
Hi David!

First of all, please excuse me for the slow reply.
I just made a compilation of a shot taken with a standard DSLR camera a (lumix fz1000) and the Chronos 1.4.
Several considerations must be done first: .
  I used a high quality light (CRI of 95) for both shots in order to eliminate light source as the possible origin of the problem.
  Also, i made a white balance on both cameras just before taking the pictures.
  The first photo is of the lumix, second is of the Chronos without any corrections and third is of the same second picture with  an exposure and whitebalance correction.

The left photo is taken with the Lumix and the colors are pretty much the same as the human eye can see.

The "problem" is that one of the green colors (the one marked in red elipse) is somewhat different from the green colour captured by the lumix.
I know it doesnt seems as much of a deal on that particular example, but this problem is much more visible outdoor with sunlight as source. Here is an example:

I am sorry i did not took a picture with the Lumix camera but I am sure the grass was way more green. It was very fresh and in the shot it seems very old almost burn from the sun.

Hope this two examples can serve you as a reference.
By the way, I have 4 ideas of what might be the problem:
1) The sensor that Chronos uses has dificulties capturing this particular wavelength
2) Mi sensor in particular happens to be a bit "bad"
3) The IR filter in front of the sensor is causing part of the problem (i could not dismount it in order to make a test shot without it)
4) The problem might be caused by saving the shot with the standard "0.70" pixel bitrate instead on something higher.

Best regards and thank you for the constant help.

Title: Re: Missing (weak) Green colours
Post by: AimedResearch on August 03, 2017, 09:20:10 PM
I doubt the sensor is lacking in sensitivity for green.  I believe it is common for sensors to be most sensitive to red, green, then blue the least.  Its not drastic, maybe a few percent in terms of quantum efficiency (I didn't look into the response of the sensor, I am guessing from what I've seen on other HS cameras).  I would suspect the optical components starting with the IR filter down to the lens.  I recently was playing around with different IR/UV cut filters for the Fastec TS3.  The results of different IR/UV filters (behind the lens), is wild.  Remember, your lens is not designed to pass IR and UV.  It is designed to pass visible light. Those wavelengths will focus at different points.  If you focus on a subject using visible light and change to a UV light, the focus will be off.  The sensor doesn't know what wavelength excites each pixel.  Only after filtering and digital processing is the color interpreted.  My experience is that high-speed cameras do not have enough native color saturation.  With expensive high-speed cameras, even if you get the color balance right,  the color is never brilliant enough.
Title: Re: Missing (weak) Green colours
Post by: A.Angelov on August 07, 2017, 07:18:12 AM
Thank you for the very interesting information AimedResearch!
Appreciate sharing your experience
Title: Re: Missing (weak) Green colours
Post by: tesla500 on August 16, 2017, 11:51:50 PM
Most color issues can be corrected in post using a color correction filter. It can be a steep learning curve, but there should be lots of video tutorials on Youtube.

There's a lot more than meets the eye in color processing in most cameras, and Chronos is no different. The main thing determining the output color is the Color Correction Matrix, which is a mathematical matrix multiply that is applied to the raw RGB data coming off the sensor. Since the color response of the whole system from camera to monitor differs from your eye's response quite a bit, there's a lot of wizardry going on to get good looking video on your monitor, and this takes a lot of work to optimize and get right. With the limited development time available so far, the color correction matrix is currently fixed to one optimized for low CRI white LEDs, which seems to work OK in most situations. You may actually get better results right now using cheap LED lighting. Better in-camera color is coming, with proper color temperature/illuminant spectrum selection.

Title: Re: Missing (weak) Green colours
Post by: John DeLonghi on September 22, 2017, 07:09:07 AM
I've been doing some lighting tests and using a color input target. Here's a frame grab which I've applied some color correction to in post, but it is close to what came out of the camera.


The greens are actually not bad. It's the magenta which seems to be lacking (the colour above the number 14). It could be corrected but would take quite a lot of tweaking.

Also remember that your monitors and output devices should be calibrated if you're going to compare like for like.