understanding the EX1r custom white balance

[Alister Chapman]

Several things going on here I expect.

ATW: Generally the electronics looks at the image as a whole and will use the brightest object in the scene as white and try to balance the image so that the brightest parts look white. This is easily fooled by bright walls that may be coloured, windows with exterior light, small lamps casting pools of coloured light etc. The indicated Kelvin reading will be for the area of the scene that the camera has chosen to consider as "white"

Manual White: You determine the white object, so have more control. However with white cards exposure is important, never overexpose as this pushes the signal up into the knee and will give erratic results. For this reason a grey card which matches skin tone brightness is preferred. Also consider where the light falling on the card (or wall) is coming from. You want to ensure the card is illuminated by the light source(s) that you are balancing for. In addition any coloration of the paper or wall will create an offset in the white balance as it tries to eliminate that tint. White printer and copier paper is often bleached or has a very small amount of blue dye as this makes it appear brighter to the naked eye, this is also true of many white paints. Beware of this as it will upset your white balance.

These are two different systems that determine white in different ways. Because of this the end result can be different and to be honest I would be more surprised if they were the same.

[Federico Perale]

Originally Posted by Alister Chapman

Several things going on here I expect.

ATW: Generally the electronics looks at the image as a whole and will use the brightest object in the scene as white and try to balance the image so that the brightest parts look white. This is easily fooled by bright walls that may be coloured, windows with exterior light, small lamps casting pools of coloured light etc. The indicated Kelvin reading will be for the area of the scene that the camera has chosen to consider as "white"

Manual White: You determine the white object, so have more control. However with white cards exposure is important, never overexpose as this pushes the signal up into the knee and will give erratic results. For this reason a grey card which matches skin tone brightness is preferred. Also consider where the light falling on the card (or wall) is coming from. You want to ensure the card is illuminated by the light source(s) that you are balancing for. In addition any coloration of the paper or wall will create an offset in the white balance as it tries to eliminate that tint. White printer and copier paper is often bleached or has a very small amount of blue dye as this makes it appear brighter to the naked eye, this is also true of many white paints. Beware of this as it will upset your white balance.

These are two different systems that determine white in different ways. Because of this the end result can be different and to be honest I would be more surprised if they were the same.

thanks but are you then saying that the area the EX1r uses to determine the white balance is different whether you use the manual or Auto balance (kind of the same way DRSL use different methods to determine the exposure)? in what way using the manual white balance "you determine the object"?
I will try tonight but in my opinion if you point the camera to a card, in the exact same position, and ask the EX1r to take the reading first manually and then automatically, the reading should be the same.
why shouldn't it be? I always think that auto white balance helps if you have gradual changes in white (say shooting outdoors for long periods) and you want the camera to slowly adapt to those conditions, but in the case of my example you are comparing like for like.

once again I am not disputing at all that manual readings are the way to go and much more accurate, I am just trying to understand if my EX1r is faulty

[Alister Chapman]

One difference is that ATW considers the entire screen area so may choose a corner or anywhere in the screen for the white balance. Manual white only uses the center 15 to 20%.

[Federico Perale]

Originally Posted by Alister Chapman

One difference is that ATW considers the entire screen area so may choose a corner or anywhere in the screen for the white balance. Manual white only uses the center 15 to 20%.

thanks. that's very interesting. that could explain my problem

[Garrett Low]

As Alister noted, ATW looks for the area that it can find that has the closest thing to bright, even colors and assumes that to be white, The camera then sets that as white which then affects all other colors in the frame. When manually setting the WB you are telling the camera what to assume is white (as mentioned on the EX cams it's the center of the frame). So by you taking the camera and pointing it in the same direction as when you took an ATW reading, and then trying to manually WB, you are actually not balancing the camera to white, You're forcing the camera to make whatever is in the center part of the frame equal levels of RGB.

The only way to tell if your camera is not functioning correctly is to use the correct procedure for manual WB.

A grey card is a very inexpensive instrument that should be an essential part of your kit, even for someone doing it as a hobby. It always amazes me when someone will spend $5K on a camera but won't spend $50 on a grey card to be able to properly white balance.

-Garrett

[Keith Dobie]

Grey vs. White? This thread from last year is worth reviewing. Check out the tests in the post on the 2nd page.
http://www.dvinfo.net/forum/sony-xdc...better-wb.html

[Doug Jensen]

Just for the record, I still stand by my posts in that other thread. My F800 doesn't lie.

[Federico Perale]

Originally Posted by Bob Grant

Federico,
at the same time can I suggest you try repeating you test with the camera stable e.g. tripod or on a table, and point it a an evenly illuminated white card. A piece of A4 / foolscap paper would be good enough for this test. Light the card with a daylight source and then repeat your experiment.

I agree with you 2500K does seem very low, the only source I've had that low is candlelight. I'm just very suspicious based on my own tests that something else is going on here.

I just re-did the test using a White A4 paper in a tungsten lit room.
The manual reading is 2500K
The auto reading is 3400K

The camera was in the exact position on a tripod and all parameters were the same

[Walter Brokx]

I suggest you try to white balance in daylight and with colored light.
Just to determine whether the costum WB does actually change.
If it does change, record your white balance process (make sure you tell us what you are doing) and post it. I have a feeling that would be a lot quicker way to find out what is going wrong. Is it an electronic failure or human error?

[Bob Grant]

Originally Posted by Federico Perale

I just re-did the test using a White A4 paper in a tungsten lit room.
The manual reading is 2500K
The auto reading is 3400K

The camera was in the exact position on a tripod and all parameters were the same

The part I've bolded might be a clue. If the card is only being lit by reflected light then it could be any CT. To conduct a meaningful test you need the light source directly lighting the card.

Under your current scenario ATW is probably getting the right answer and so is manual WB. The problem isn't with the answer, the problem is the question :)

[Doug Jensen]

Originally Posted by Walter Brokx

I suggest you try to white balance in daylight and with colored light.

Also, do it with no PP selected so you eliminate those menus entirely from the white balancing.

[Federico Perale]

Originally Posted by Walter Brokx

I suggest you try to white balance in daylight and with colored light.
Just to determine whether the costum WB does actually change.
If it does change, record your white balance process (make sure you tell us what you are doing) and post it. I have a feeling that would be a lot quicker way to find out what is going wrong. Is it an electronic failure or human error?

I hold an A4 paper opposite to the light source then point the camcorder so that all the image I am seeing is white then press the white balance button. will try tomorrow morning to do the test in daylight and post the results

Originally Posted by Bob Grant

The part I've bolded might be a clue. If the card is only being lit by reflected light then it could be any CT. To conduct a meaningful test you need the light source directly lighting the card.


Under your current scenario ATW is probably getting the right answer and so is manual WB. The problem isn't with the answer, the problem is the question :)

I have the light source directly lighting the card. the reading doesn't really change much though. and always stays around 2500K (2400/2600)

Originally Posted by Doug Jensen

Also, do it with no PP selected so you eliminate those menus entirely from the white balancing.

sure...all these test are being done with no PP selected

[Garrett Low]

Originally Posted by Federico Perale

I hold an A4 paper opposite to the light source then point the camcorder so that all the image I am seeing is white then press the white balance button.

Try to hold up a few pages of the white paper to ensure you are not getting any bleeding through from a light source behind the paper. Most paper is think enough where colors coming from behind the page start to show through. Also make sure your exposure is set correctly before taking your WB reading.

-Garrett

[Federico Perale]

Originally Posted by Walter Brokx

I suggest you try to white balance in daylight and with colored light.
Just to determine whether the costum WB does actually change.
If it does change, record your white balance process (make sure you tell us what you are doing) and post it. I have a feeling that would be a lot quicker way to find out what is going wrong. Is it an electronic failure or human error?

hi Walter
this morning I tried the daylight test
it's a cloudy day so not full sunshine

I used the A4 paper in different positions and every-time took the manual reading and then the automatic reading for comparison. I also took different measurements using the white wall (sorry Doug! : ) ) - all measurements were taken with no Picture Profile selected, and never using Full Auto

1) paper placed near the window so that it gets direct daylight: manual 9200K, automatic 9200K
2) white wall near the window: manual 6600K, automatic 6700K
3) wall inside the room (not directly lit): manual 5000K, automatic 5000K
4) looking outside of the window: manual 6500K, automatic 6800K

afterwards I went into a tungsten lit room and redid the test with the A4, and once again the results were quite different: manual: 2800K, automatic 3500K

so my point is that from my tests it seems like my EX1r shows very little variance when measuring white balance from natural light, and results are either identical, or vary in the order of 100K,

when measuring white in artificial light, I keep seeing a far wider difference, in the order of 600/1000K, and often I have the impression the manual reading is too cold

[Alister Chapman]

9600K from your paper and 6600K from the white wall suggests the paper is not white, but blue or contains dyes designed to make the paper look bright and white to the naked eye. 6600K is a much more sensible reading from an overcast sky.

I don't know why you are seeing such variations under tungsten light, but I'm still not surprised that there are differences. They are two different systems.