How do you color calibrate a camera?

[drakejest]

Hello,

I have 5 ptz cameras and i noticed when i all point them to a single object the image looks different even though they all have the same video settings. This is bothering me and i would like to do something about it. I am satisfied that the cameras are not super color accurate, but what im particular is consistency between cameras.

Notice here its the same colored shirt but the color is different.



I was probably thinking of buying something like this. Of course its not the professional grade this one cost 20$ ,



My problem though is i dont know how to use it. I know the known values of the test colors but i have no idea how to convert them into the values needed by the camera





Anyone else encountered this problem and how you fixed it?

 

[looktall]

Would this not just be white balance?

 

[drakejest]

Would this not just be white balance?

Maybe, but how do i adjust the RED and BLUE values of white balance? it will take me forever to jst trial and error all 5 cameras

 

[biggen]

Maybe, but how do i adjust the RED and BLUE values of white balance? it will take me forever to jst trial and error all 5 cameras

Is the lighting uniform? If you have different color temps of ambient lighting for the different cam locations then that will affect color rendering. If you took 5 exact cams with the exact settings to the exact same location with the exact same lighting conditions and then pointed them all on the exact object then I’d expect rendering to be similar assuming all cam settings were normalized.

Out of the 30 cams I own, only one has to be set to a manual WB at night because of a high pressure sodium street lamp that illuminates the sidewalk the cam is watching. If I use an “auto” WB I get a terrible yellow hue at night on the cam footage. So I had to go to manual WB and increase the Blue to 100% and decrease the Red to 0%. That removes all the yellow that lamp produces and renders colors much more accurately of people walking under it. I can only do this at night though and I have to delay the night time profile switchover of the WB to half an our after sunset and the switchover back to auto WB for the daytime profile to half an hour before sunrise. If I don’t, ambient sunlight available will turn the entire scene blue because of the values I have to use to adjust out the lamp yellow. So I have to make sure there is zero sunlight in the scene before I adjust the WB.

If your cams are in locations with varying lighting throughout the day, you are gonna have to leave WB alone. A manual WB is designed to be used with a uniform (e.g. never changing) color temp. Any color temp change would require redoing the manual WB values. When I use to work in the news industry years ago, all our studio and field photog cams used manual white balance. Before any shooting of video would occur, one would have to point the camera at a white object and then hit the "WB" switch on the camera. That would instruct the camera that the object it is seeing is white so it needs to adjust it's values accordingly to render it white. You will see reporters (or their photogs) on the street sometimes pointing their cameras at a person with a white shirt or holding a piece of white paper in front of the camera. They are white balancing the camera before they start recording. If the lighting ever changes (e.g. clouds roll in after you just white balanced with clear skies) then they have to WB again.

My Dahua cams have no way to point them to a white object to calibrate their WB like those $10k - $20k news/production cameras do. You either set them to auto and let them try to determine color temps (via a sensor and algorithm I'd guess), give them a predefined color temp (e.g. day, street lamp, fluorescent lamp, etc..), or set them to manual and pick your "best guess" by adjusting the red and blue sliders.

Also, I will say to make sure your camera settings are the same across them all as well. Using WDR can really effect colors bigtime from my experience with my Dahua cams. On the 5442's it will wash out colors and make them look dull. However, on the 4k-t cams, it will make colors look waaaay oversaturated and give them a cartoony look. I try not to run any back light compensation if I don't have to since it screws up the colors so much.

 

[Perimeter]

On the dahua's, for manual adjustment, I found it easiest to use the last WB option (with a frame). Move the frame about, you will quickly discover how to place it to get the balance of your preference. Accept the result, then switch to manual to fine tune. YMMV.

 

[drakejest]

Is the lighting uniform? If you have different color temp of ambient lighting for the different cam locations that will affect color rendering.

Fortunately yes ! these cameras are indoors so the light is consistent. The only inconsistency is the position of the camera, one of the camera (the one that took the greenish shirt) is placed on the dim area but since its a ptz its zoom is set so that only the area with lots of light is on the frame (i wonder if that is what is messing up the auto WB)

I have also tried all the other presets but they dont seems to get the color quite well, which I hope i can get better results with the manual one. How do know when you have to much or to little red or blue. My camera only has sliders for red and blue ( i wonder why there is no green)

 

[drakejest]

My Dahua cams have no way to point them to a white object to calibrate their WB like those $10k - $20k news/production cameras do. You either set them to auto and let them try to determine color temps (via a sensor and algorithm I'd guess), give them a predefined color temp (e.g. day, street lamp, fluorescent lamp, etc..), or set them to manual and pick your "best guess" by adjusting the red and blue sliders.

I have done a bit of reading and came up with an idea of taking a screenshot of the image and using photoshop do determine the RGB value of something grey (i guess i would print out a 50% grey or use the color calibrator) a 50% gray should have an rgb value of 128,128,128. I guess if the values are not equal thats when i need to add or subtract, since only red and blue slider are the only thing available i would have to match the green value.

 

[Perimeter]

Green is relative to red and blue. If you decrease red and blue, the pic gets more greenish and vice versa.

 

[drakejest]

On the dahua's, for manual adjustment, I found it easiest to use the last WB option (with a frame). Move the frame about, you will quickly discover how to place it to get the balance of your preference. Accept the result, then switch to manual to fine tune. YMMV.

what do yo mean by "last WB option (with a frame)" do you mean the last one in the selection(day, street lamp, fluorescent lamp, etc.. )?

Green is relative to red and blue. If you decrease red and blue, the pic gets more greenish and vice versa.

ahhh so i can adjust the green then, if i have to much green i just have to increase red and blue by the same amount. Thats so clever!

 

[Perimeter]

what do yo mean by "last WB option (with a frame)" do you mean the last one in the selection(day, street lamp, fluorescent lamp, etc.. )?

Yes:"regional custom". It gives you a frame for which it does the WB. It allows you to custom shift the balance, just experiment a little. This way, you can eliminate objects with distracting color.

 

[Alaska Country]

One way to match (not tested) between cameras is to try the following.

1) In WB settings choose either auto or natural and save.

2) In WB setting select "Manual". The red and blue values should be displayed for your settings in step one.

3) On your second camera for WB use "Manual" and use the same red and blue numbers. This may not work or still could display a color shift due to sensor/camera differences, etc.

Alternative suggestion

1) Use a piece of white 20 pound paper (printer paper) and tape to each side of the camera with space between the paper and lens.



2) Select "Auto" and save.

3) Select WB "Manual".

3) Decrease both the red and blue to zero. Image (paper) should be now be green.

4) Increase "Red" to a a nice yellow paper. - not orange.

5) Increase "Blue" to turn the yellow into a neutral gray (muddy looking white).

6) If too pink reduce the "Red" a few points.

7) Save

8) Remove paper and see if the colors are to your liking.

Using this procedure the camera will try to make the image 18% gray. That is your goal.

The overall issue is that green is set at 50% and one can only adjust the red and blue with manual. Thus the RGB reading from PhotoShop may not be of use unless the green can be adjusted to 50% and only vary the red and blue.

How well this color procedure works or even it is is feature on all Dahua cameras is unknown.

To get exact color numbers it may be necessary to look at the products offered by Color iMatch Formulation Software (xrite.com). Not inexpensive.

Have used their products in the past to match a color monitor to color printer output. So WYSIWYG in this case, worked very well.

 

[Alaska Country]

One could also try a color picker for Windows to read the screen (monitor) RGB value. Included in Micosoft Power Tools is a free screen color picker. With a mouse over it will read the screen color in RGB and HEX. Perhaps a solution to professional costly devices as only a crude reference is needed to get in the ballpark.

 

[drakejest]

Yes:"regional custom". It gives you a frame for which it does the WB. It allows you to custom shift the balance, just experiment a little. This way, you can eliminate objects with distracting color.

I do not have a regional custom on my choices, maybe because im using an old model

 

[Perimeter]

What does ATW do?

 

[drakejest]

What does ATW do?

nothing that i notice, it has no other options, just like auto. only manual has some sliders in it

 

[DanDenver]

“ATW is a more dynamic version of AUTO white balance. It detects when your ambient lighting shifts significantly (such as moving from indoors to outdoors) and dynamically changes the AWB for you.”

Here is the WIKI from Dahua related to camera settings

Sounds like you want to avoid any of the auto settings. So I would avoid the ATW setting and only use manual in the WB dropdown as well as any other configurations that would automatically change the image. You indicate you have a controlled lighting setup which is unusual, but with such a thing you might try operating all possible settings on manual so that you can maintain full control at all times. Basically, if nothing ever changes, then no auto setting will add value and will only try to make unwanted adjustments on the fly. Any auto setting will - by definition - cause each camera to potentially have different settings

 

[drakejest]

Update

while waiting for the calibration tool , i played with the hue settings on the smart pss, not in the website setting as there is no hue slider there (check image on the first post) . i was able to roughly match the color, still barely noticeable but not as obvious as the image.

So it might not be white balance, or it cold still be + some adjustment on the hue/contrast