Solved Colours of camcorder not as expected

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Colours of camcorder not as expected was created by Patek

Hello,

the colours of the films/photos of my Sony HDR 810 camcorder are not as I expected.
There might be two reasons: Maybe the camcorder is wrong, maybe my expectations are wrong.

It started with the zebra function of the camera. The segments of the photo marked by the Zebra 100 function as 'overexposed'
were sometimes considerably underexposed, sometimes overexposed. Also, the colours of the film/photo do not look really like the objects I filmed (with manual whitebalance) when viewed on my calibrated monitor (calibration/profiling with dispcalgui, xrite i1 display pro).

So, I made a simple test:
I displayed a white picture on my monitor (60 Hertz), rgb=255,255,255.
I set the white balance of the camera to this motive.
I took a photo. F/4, 1/60 s, monitor screen out of focus to avoid Moiré. Cinetone and all other image functions switched off.
I analysed the photo in gimp with the colour histogram function:
The result was rgb=164.3 164.8 163.3. (Each number is the average of its channel.)
The colour channels agree (quite closely) which is as expected, since the whitebalance was based on the motive.

Now I took photos of the following pictures red, green, blue, yellow, magenta, cyan:
255,0,0
0,255,0
0,0,255
255,255,0
255,0,255
0,255,255.

I expected in the gimp analysis that the 255 is simply replaced by 164 in the histogram. But it was not.
Here are the results:

255,0,0 became 184 0 4
0,255,0 became 4 187 0
0,0,255 became 17 0 241
255,255,0 became 147 180 0
255,0,255 became 163 0 239
0,255,255 became 53 169 179.

Apparently, the yellow motive looked very greenish in the photo.
And the magenta was a lot on the blue side.
Also, this behaviour might explain why the zebra function is wrong for some (real-life) motives, e.g.
the sky is always heavily clipped even though the zebra 100 is far from signalling overexposure:
White (255,255,255) is far from clipping, ca. 164 in each channel. But blue (0,0,255) is already close to clipping, ca. 241 in the blue channel.

These are massive deviations from the correct colour.
So, maybe something was wrong with my setup. Or is the camera wrong?

I am aware that the motive is unusual in the sense that its spectrum has three rather
narrow bands (red, green, blue) in contrast to regular motives. But since white (255,255,255)
is measured correctly by the Sony camera, why would the subset of colours (255,0,255) etc. be measured incorrectly?

Thanks for any suggestions.
30 Apr 2016 02:21 #1

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Replied by Eagle Six on topic Colours of camcorder not as expected

Hi Patek,

Unfortunately I'm not going to be of any help. I don't have a Sony HDR 810, nor can I get my hands on one, to send you a test source file which you could use as a comparison. Although I have Gimp, my knowledge of the program is pretty much nil.

Outside of that, in the past when I have done analysis, and the results were unexpected, I have double checked the origin and steps to confirm I was not making a mistake. I have also written out those steps and followed them in reverse to help identify anywhere I may have failed to apply the correct method.

If your test are correct, from what I can understand of your post, it appears there may be a massive malfunction of your camera. Is this a new camcorder? Have the colors always been off? If so, I think your suspicion that the camera is out of calibration, may be correct and time to have it serviced.

If you haven't already, and you don't get another response here, you may want to post on the Gimp forums, maybe they can help.

I'm sure you have thought of all this, but at least I wanted to make a reply, even if it was in desperation, and of little help.
Best Regards......George
02 May 2016 02:07 #2

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Replied by Patek on topic Colours of camcorder not as expected

It is a new camcorder indeed, I purchased it this year.
I will then consider to post this question in the gimp or a display calibration forum.

Thanks for your feedback.
Have a nice day!
03 May 2016 07:03 #3

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Replied by Eagle Six on topic Colours of camcorder not as expected

Hopefully another member here will respond also. Hope you will update us when you find the solution and/or possible cause.
Best Regards......George
03 May 2016 07:47 #4

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Replied by Patek on topic Colours of camcorder not as expected

Here is an update after some research and asking questions:

In short: I made some progress but the main questions are still open.

First, taking photos of a monitor screen can be a challenge because the screens have very peaky spectra.
In contrast, a real-life object has a more even wavelength spectrum which is easier to assess by a CCD.

Second, I checked the colour profile of my camera: it is sRGB.
(In fact, it is not exactly. There are different PAL colour standards - which is surprising in itself.
The standard followed by Sony has a very slight deviation from sRGB on the green component.)

Third, my camera has three white balance options: indoor, outdoor and manual.
In all three cases, the camera changes the colours of the taken photo in a way that is
undisclosed by Sony. As a result, there is no way to directly get the accurate colours of the object.
Correct colours could only be achieved by calibrating the camera (i.e. choosing a fixed white balance, either indoor or outdoor),
and then profiling the camera with a colour chart.

I have made not really progress on my initial question to understand what the zebra function of my camera is in fact doing
and why it is wrong in so many cases (underexposing or overexposing).
What I know is that I will definitely find it out before I ever consider to upgrade to another camcorder. Correct exposure should
be ensured by the camera. Maybe histograms will do the trick. But even professional photocameras pose problems to users on histograms:
In many cases histograms refer to the jpeg rather than the RAW image.

So far for the moment.
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10 May 2016 07:52 #5

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Replied by Eagle Six on topic Colours of camcorder not as expected

Hi Patek,

It appears you are making progress. Here is just some more rambling that probably will not help and you are most likely aware of......

We know that using a zebra pattern is extremely accurate for exposure, although the perfect exposure may not produce what we feel is the perfect color. We also know the success of using the zebra pattern is based on selecting the correct IRE (Institute of Radio Engineers) for the primary subject. We know 110 IRE will clip the whites, and we should use 100 IRE to adjust for whites if that is a part of our primary subject. Somewhere around 75 IRE is good to use for normal Caucasian skin tones, but the range maybe from 70-80!

But regardless of the IRE setting, we need to know which IRE setting our camera is set on to properly use the zebra pattern. I usually use the zebra pattern in conjunction with RGB parade, vector scope, luma overlay, and dynamic range. Of course none of them agree, but if I have time I use them and sooner or later pick a setting that seems to fit the best! As we know, when there is no time, we have to switch it to 'auto' and deal with the results in post.

If you have some white snow in sunlight, or bright white painted exterior wall in sunlight, or even a pure white (usually referred to as 'Brilliant 100%') sheet of paper (although we know there is no true white paper, at least not easily available) in sunlight and we use the zebra pattern to adjust the exposure when set to 100 IRE and our exposure is off by a margin, then either the camera censor may be at fault, or the IRE setting is at fault, or perhaps you don't have an IRE adjustment in your camera and the fixed setting it does have isn't calibrated for 100 IRE.

I have never had a camera that provides perfect exposure. I do have a camera that comes close and pleases me. It does even better when I use the Atomos recorder, which has additional tools, and I have the time to make critical adjustments. I'm also prepared to always need to make color and exposure adjustments in post to satisfy my personal taste, even if those taste are not widely enjoyed by others.
Best Regards......George
10 May 2016 09:24 #6

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Replied by Patek on topic Colours of camcorder not as expected

My Sony HDR PJ 810 has the IRE settings 70 and 100. It is the same menu setting for video and photo.

The simplest example that sth is wrong is the following:
The blue sky is overexposed (clipping in blue channel, 8 bits) even though the IRE 70 zebra does not show any overexposure.

Well, I call it "wrong", but maybe this follows the specifications by Sony.
I have read that some cameras compute the zebra function on a weighted sum of the rgb channels.
Other cameras base the zebra only on the value of the green channel. Reportedly, older Nikon photo cameras belong to this group.

In both these cases, the overexposed blue sky would be consistent with the implementation because (basically) only the blue channel
is recorded in the blue sky scenario. Since the other channels are missing, the weighted sum (or only the green channel) would
display as "not overexposed" even though the blue channel is.
Consistency in implementation could still lead to wrong information on exposure.

What I am looking for is a zebra function based on the maximum of all three channels.


I will post my findings, the search is on :)

PS: I have based my analysis on the jpg photos of my camera so far because they are easier to analyse than the video.
I think it does not matter much because the videos of the sky looked the same as the photos on my monitor.
I will check whether Vegas provides these types of functions for video as Gimp does for photos.
11 May 2016 02:47 #7

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Replied by Patek on topic Colours of camcorder not as expected

update:

by the help of some video tutorials (also here on MSZ :) ) I have now found out that the video scopes provide the right tools to analyse the rgb components of a track. By the way, I am lucky to have purchased Vegas Pro rather than Movie Studio Platinum - I was not aware of that feature at the time of purchase.

The video shows the same overexposure as the photos, so I have to follow this up.

To find out the underlying behaviour of the zebra function of my camcorder, I guess that a forum on Sony camcorders might provide some info.
The following user(s) said Thank You: Eagle Six
17 May 2016 00:48 #8

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Replied by Eagle Six on topic Colours of camcorder not as expected

Thank You Patek, for the update.

Some of the reasons I upgraded from Movie Studio to Vegas was the scopes and scripting. The scopes have been beneficial, as well as, very interesting using and developing a workflow.


Patek wrote: To find out the underlying behaviour of the zebra function of my camcorder, I guess that a forum on Sony camcorders might provide some info.


This was my thought a while back, but not being a Sony camera users I have no idea where a forum is located. I'm sure you will find something, and hopefully it will have some expertise to answer your question.

I commend you on your persistence and patients running this down.
Best Regards......George
17 May 2016 02:27 #9

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Replied by Patek on topic Colours of camcorder not as expected

Hi, one more update.

My question was not answered in the Sony community forum.

It seems that there is a mismatch between my high level of ambitions on exposure (control of clipping) and
the low-medium level of my camcorder.

If someone cares for clipping control in all colour channels then this person has a higher level video camera.

And vice-versa, oweners of low-medium level camcorders do not care about clipping as long as the overall
image is "more or less" ok. I guess that few of them have the necessary tools (video scopes in Vegas Pro) to
identify clipping in videos, anyway.

So, my conclusion is:
I have to be aware that my camera tends to overexpose (i.e. underestimate in exposure control) the red and blue colours.
Green and white are ok. And if I upgrade to another camera sometime then I will consider the correctness of exposure control tools.

Thanks for all the feedback, so far.
01 Jun 2016 01:20 #10

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