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White Balance: Episdode II
This is not so much an XL-1 issue but I hope it is okay to post it.
I have been thinking a lot about white balance over the last couple of days and I have begun to confuse myself. To correct tungsten, 3200k light, to dayliight, I use a blue colored gel. If I place this gel in front of my lens when setting white balance the colors in effect warm up some degree. I believe in this instance I am subtracting blue, is that correct? On the other hand, if I place the blue gel in front of the tungsten light source to correct it to daylight, is it still a subtractive process? I want to say no but I can't explain why. If that is the case, why would a "minus green" gel be magenta in color? If I want to subtract green in the same manner I am subtracting blue, wouldn't the correct gel be a green color? I know that is not the case since they are magenta but I haven't figured out why. I enjoy technical descriptions so feel free to elaborate. Thanks. Greg Matty |
reply
--To correct tungsten, 3200k light, to dayliight, I use a blue colored gel.--
"thats right, when converting 3200K light to 5600K light (daylight) you would use a CTB filter. --If I place this gel in front of my lens when setting white balance the colors in effect warm up some degree.-- "no, when using a CTB filter your image will look cooler, not warmer. but when using a CTB on your lens and then pointing your cam to a white card and then white balance your image would look normal, but when you remove your filter from the lens, your image will look warmer." --I believe in this instance I am subtracting blue, is that correct?-- " no, you are substracting orange, wich makes it look more blue" --On the other hand, if I place the blue gel in front of the tungsten light source to correct it to daylight, is it still a subtractive process?-- "yes, lighting with filters is a substractive process" --If that is the case, why would a "minus green" gel be magenta in color? If I want to subtract green in the same manner I am subtracting blue, wouldn't the correct gel be a green color?-- "no, if you would add a green filter your lamp would look even greener, thus you are adding green, but you want to substract green, on the basic color wheel, on the other end of green is magenta, thus to get a less green light you would need to add a magenta filter. when doing this you are substracting green" "i hope this is what you wanted to know, if you want to know anything else, just reply to this message and ask, another good place to look about Colorimetry is http://www.cameraguild.com/technology/index.htm" Bryan Johannes Onel. Director and Director of photography. Amsterdam, The Netherlands. |
Bryan,
Thanks for the help and responses that were not condescending. I need to read your post a few more times to really get it down but you explained it very well. It sound like the gels has different effects if placed in front of the lens for setting white balance and placing it in front of a tungsten lamp to CTB. Thanks again. Greg Matty |
one more thing...
one more thing,
CTB stands for color temp. blue. CTO color temp orange. if you are shooting indoors with tungsten light and are shooting with a daylight balanced camera you would need to place a CTB in front of your lens. filters don't look the same way on camera as they do in real life, if you have a HMI lamp wich is 5600K and you are shooting with a daylicht balanced camera or film it would look normal, but when you would add CTO to make it look a bit warmer it may look beatifull to your eye, but on camera it will be way more orange. so what people do to make something look warmer or cooler they use half, quarter or eighth filters, like 1/2 CTO, 1/4 CTO, 1/8 CTO. you can also combine these : 1/8 CTO + 1/8 CTO + 1/8 CTO = 3/8 CTO. it is not adviced to mix CTO and CTB !!! and forget about the term white balance, proffesionals don't use white balance, just think about the two standars tungsten and daylight, and work from there. for more questions just ask! goobye |
Re: one more thing...
<<<-- Originally posted by bryanthedirector : one more thing,
CTB stands for color temp. blue. CTO color temp orange. if you are shooting indoors with tungsten light and are shooting with a daylight balanced camera you would need to place a CTB in front of your lens. Bryan, This sounds like a great shortcut. If I have four tungsten lights in a scene and wan't them all corrected to blue, I can just place a CTB filter on the camera instead of adding gels to each light. That is almost too simple. I suppose the only time this won't work is if I have several windows with bright daylight spilling onto the scene. In this instance, a CTB filter on the camera would over compensate the daylight. If there aren't too many windows and they aren't too large, I guess the best thing to do would be to place a yellow/straw colored gel over the outside of the windows to do the CTB thing and leave the tungstens as is. Is that about right? Lastly, to keep the window from appearing over exposed, I know I can place an ND gel over the window to cut down on the amount of light coming through. Can I use a straw gel and an ND at the same time? Lastly, lastly, large sheets of ND gel aren't real cheap. Any idea if .3,.6 or .9 would be best for bright sunlight? If I had the cash I could buy all three but that is too expensive right now. Thanks for the help. Greg Matty filters don't look the same way on camera as they do in real life, if you have a HMI lamp wich is 5600K and you are shooting with a daylicht balanced camera or film it would look normal, but when you would add CTO to make it look a bit warmer it may look beatifull to your eye, but on camera it will be way more orange. so what people do to make something look warmer or cooler they use half, quarter or eighth filters, like 1/2 CTO, 1/4 CTO, 1/8 CTO. you can also combine these : 1/8 CTO + 1/8 CTO + 1/8 CTO = 3/8 CTO. it is not adviced to mix CTO and CTB !!! and forget about the term white balance, proffesionals don't use white balance, just think about the two standars tungsten and daylight, and work from there. for more questions just ask! goobye -->>> |
hey greg
Greg,
i have written a small article for you, i hope you will understand it, i think it will be a little too much for you in one time, but if you read it 2 or 3 times you will understand it i think. because i couldn't upload here i have put it on a webpage. www.jrwilliams.pwp.blueyonder.co.uk/article.htm its pretty long but i tried to write it comprehensivly, at least i had fun writing it. for any other questions just ask. and something else, anyone who needs some help with cinematography. light or any subjects just ask me and i would be happy to write an article for you people. goobye |
The site (dvinfo.net) greatly benefits from articles submitted
by others, especially knowledgeable people! So, please, if you have time to spare write us an article. I've written one on my first movie experience. Thanks! |
Bryan,
Thanks for the article. That will help a lot of people. Greg Matty |
Re: reply
Bryan,
I have re-read this response and something appears contradictory. <<<-- Originally posted by bryanthedirector : --To correct tungsten, 3200k light, to dayliight, I use a blue colored gel.-- "thats right, when converting 3200K light to 5600K light (daylight) you would use a CTB filter. --If I place this gel in front of my lens when setting white balance the colors in effect warm up some degree.-- "no, when using a CTB filter your image will look cooler, not warmer. but when using a CTB on your lens and then pointing your cam to a white card and then white balance your image would look normal, but when you remove your filter from the lens, your image will look warmer." --I believe in this instance I am subtracting blue, is that correct?-- " no, you are substracting orange, wich makes it look more blue" Bryan, In your second statement above this one, you mention that the image, "will look warmer." This seems contradictory. Certainly wamer is yellow/orange and not blue. Can you clarify this? Thanks. Greg Matty --On the other hand, if I place the blue gel in front of the tungsten light source to correct it to daylight, is it still a subtractive process?-- "yes, lighting with filters is a substractive process" --If that is the case, why would a "minus green" gel be magenta in color? If I want to subtract green in the same manner I am subtracting blue, wouldn't the correct gel be a green color?-- "no, if you would add a green filter your lamp would look even greener, thus you are adding green, but you want to substract green, on the basic color wheel, on the other end of green is magenta, thus to get a less green light you would need to add a magenta filter. when doing this you are substracting green" "i hope this is what you wanted to know, if you want to know anything else, just reply to this message and ask, another good place to look about Colorimetry is http://www.cameraguild.com/technology/index.htm" Bryan Johannes Onel. Director and Director of photography. Amsterdam, The Netherlands. -->>> |
greg,
what i mean is this indeed when using a CTB filter on your lens your image will look cooler, but then point your camera at a subject that is white like a white card, then white balance, your image will not look cool anymore, but it will look normal, by white balancing the color temp of your camera has changed. but now if you keep that white balanced setting and remove your blue filter, your image will look warm, and if you place the CTB filter in again it will look normal. you get it? bye |
Bryan,
I got that part of it just fine. It is the following that confused me. --If I place this gel in front of my lens when setting white balance the colors in effect warm up some degree.-- "no, when using a CTB filter your image will look cooler, not warmer. but when using a CTB on your lens and then pointing your cam to a white card and then white balance your image would look normal, but when you remove your filter from the lens, your image will look warmer." --I believe in this instance I am subtracting blue, is that correct?-- " no, you are substracting orange, wich makes it look more blue" We both agree that after setting the white balance with the blue gel and then removing the blue gel, the image will appear warmer. This makes sense for obvious reasons. It is your statement above where you say, at least I think you say, that using a blue gel subtracts orange which makes the image appear more blue that seems the opposite of what was just said. If we both agree that the image appears warmer, then it shouldn't appear more blue correct? Maybe you are referring to the orange subtraction and a blue image while the gel is STILL in front of the lens? I was referring to after the gel was removed when the colors appear warmed up and of course then you are not adding or subtracting anything. I think I get it now. Greg Matty |
BIG question
I was silently following your discussion here and picking up things secretly, but the more I read the more questions show up..
1. Letīs say I want to shoot a living room at night with the existing light (all of it common incandescent household light bulbs of the same make that burns at around 2900K or whatever). If all lights are of the same colortemperature, then I just manually whitebalance my XL1 with a sheet of white paper or a 18% bounce card. The image should look normal and the bulbs themselves be a white spot and not a reddish one, right? 2. My confusion came from the film-industry where the lights used are either 3200K or 5500K because filmstock is balanced to either tungsten (3200K) or daylight (5500K) and film is fixed to these temperatures. With a videocamera we can whitebalance to any source of light as long all light sources are of the same colortemperature, right? 3. When shooting a sunset/sunrise: Manual whitebalancing makes no sense because I would lose the red/purple cast in the sky, is this correct? Should I balance to 5500K daylight the get the real image I see with my eye, use the 3200K setting or is it a matter of taste how "romantic or dramatic" the sunrise should look? 3a. Generally when shooting outside with the sun as lightsource: Setting the camera to 5500K will give me the correct look of the day: White at noon and more reddish toward dawn and dusk, right? But when shooting I have to manually white balance every couple of minutes to keep color-continuity to match the shots in the editing. But a late afternoon will then look like noon (lightwise) except for the long shadows, right? How do I get back the afternoon colortemperature? Shall I put a filter on the lens or correct in post? Now some "inventive" questions: 4. Reflectors (the real ones and any surface like walls): Are they basically filters? A silver reflector gives a cooler look than a golden one. Except for not being able to redirect light, would I get the same result if I put a ND gel plus a colorcorrection gel in front of the light to get the light that would be reflected by a reflector 5. The work lights that have been mentioned: Are these halogen lights? They burn at around 3200K, right? Does the same go for those small 20-35W coneheaded bulbs with the little mirrors inside? (sorry for the odd description, I have no idea what they are called in english) 6. Is there a difference in colortemperature at different wattages (125W, 500W, 1500W)? There shouldnīt be any. The thickness of the wire determines the resistance for the current flowing through it and therefore the wattage: Burning at the same tempertature, right? 7. Lets say I have a light source that emits pure RED light and zero green and blue. No white balance possible, right? The camera would try to reduce the voltage for red and increase the blue and green channels resulting in no signal at all and a black image. PS: BRYAN: The eggs are in the mail and on the way to you. Thanks to our superfast austrian postal service they will surely be completely rotten and stink like hell when you get them. Canon better acts quickly! :-)))) Cheers, |
Re: BIG question
<<<-- Originally posted by Peter Koller : I was silently following your discussion here and picking up things secretly, but the more I read the more questions show up..
1. Let?s say I want to shoot a living room at night with the existing light (all of it common incandescent household light bulbs of the same make that burns at around 2900K or whatever). If all lights are of the same colortemperature, then I just manually white balance my XL1 with a sheet of white paper or a 18% bounce card. The image should look normal and the bulbs themselves be a white spot and not a reddish one, right? That?s right, but for white balancing you should not use a grey card, a white card should be used, its called "white balancing". Because the camera tries to make the white card look white, so if the white card would look a bit orange on screen, it would become white. But forgot about the whole term white. balancing, white balancing is not such a good thing because of continuity, the white balance will mostly vary a bit because of reflections, wrong direction it points to, for real colour correction just rent a box of filters, but for standard field work (one man crew) white balancing is the way to go, it would be impossible to change filters during a football game or something! 2. My confusion came from the film-industry where the lights used are either 3200K or 5500K because film stock is balanced to either tungsten (3200K) or daylight (5500K) and film is fixed to these temperatures. With a video camera we can white balance to any source of light as long all light sources are of the same colortemperature, right? that?s right. 3. When shooting a sunset/sunrise: Manual white balancing makes no sense because I would lose the red/purple cast in the sky, is this correct? Should I balance to 5500K daylight the get the real image I see with my eye, use the 3200K setting or is it a matter of taste how "romantic or dramatic" the sunrise should look? Well, it wouldn?t make sense indeed, but it wouldn?t look white, it would still look orange because of white balance?s limited range. For balancing to 5500K or 3200K is a matter of taste, but I would go with 5500K and then cool it down a bit if it?s too warm. 3a Generally when shooting outside with the sun as light source: Setting the camera to 5500K will give me the correct look of the day: White at noon and more reddish toward dawn and dusk, right? Yup, the later the day, the warmer it gets, but when it gets darker, the colour temp of the sky rises to about daylight again, but simulating daylight at night is a pure matter of taste. But when shooting I have to manually white balance every couple of minutes to keep colour-continuity to match the shots in the editing. But a late afternoon will then look like noon (light wise) except for the long shadows, right? How do I get back the afternoon colortemperature? Shall I put a filter on the lens or correct in post? Correcting in post is a terrible job and not advised, what I would do is use my color meter to measure, shoot at a normal temp like 3200K or 5600K filter it to a tungsten or daylight temp, then you have a normal picture, no reds, no blues, just a normal pic, from that I would later on make it look warmer or cooler in post, the advantage of this is that when shooting you are keeping colour continuity, when applying a colour effect in post you can do it to the whole timeline in one time and it will be continuous. Now some "inventive" questions: 4. Reflectors (the real ones and any surface like walls): Are they basically filters? A silver reflector gives a cooler look than a golden one. Except for not being able to redirect light, would I get the same result if I put a ND gel plus a colorcorrection gel in front of the light to get the light that would be reflected by a reflector. Silver and gold reflectors aren?t the most used lights, normally people just use white bounce surfaces. But when using a silver or gold reflector on location don?t think of it as a filter. The silver just bounces the normal light with the same colour temp but the light coming from it is soft but not as soft as when using a bounce card. For the gold reflector, it does make the light look warmer, these could be used to simulate a sun backlight for example, how warm you want the sun to be is a matter of taste. 5. The work lights that have been mentioned: Are these halogen lights? They burn at around 3200K, right? Does the same go for those small 20-35W cone headed bulbs with the little mirrors inside? (sorry for the odd description, I have no idea what they are called in English) I have no idea is they are halogen, but most normal household lights burn at a color temp of around 2900, it may be 300 K difference with the standard, but this is noticeable on screen. 6. Is there a difference in colortemperature at different wattages (125W, 500W, 1500W)? There shouldn?t be any. The thickness of the wire determines the resistance for the current flowing through it and therefore the wattage: Burning at the same temperature, right? Of course, all wattages lights burn at the same temp when using the same type of light source. But if you connect your lights to a dimmer and dim your lights down the colour temp will get lower (warmer), so the best way to dim a light is to use scrims or nd?s. 7. Lets say I have a light source that emits pure RED light and zero green and blue. No white balance possible, right? The camera would try to reduce the voltage for red and increase the blue and green channels resulting in no signal at all and a black image. well, white balacing has a limited range, it can go (this is what i saw in theory) from about 2600K to 9000K (or higher, sometimes daylight can have a real high temp). what i said here (question no. 7) is not something i am entirely sure about, all i know is that white balance has a limited range. you should ask a video pro about this (im a proffesional with film, i have some video knowledge but not about electronics like white balance and such). PS: BRYAN: The eggs are in the mail and on the way to you. Thanks to our superfast austrian postal service they will surely be completely rotten and stink like hell when you get them. Canon better acts quickly! :-)))) Cheers, -->>> If i forgot something, let me know! C ya |
Bryan and Peter...this is one of the most detailed exchanges I've ever seen. Thanks to both of you for the info...and to everyone else on this thread.
|
That?s right, but for white balancing you should not use a grey card, a white card should be used, its called "white balancing". Because the camera tries to make the white card look white, so if the white card would look a bit orange on screen, it would become white. But forgot about the whole term white. balancing, white balancing is not such a good thing because of continuity, the white balance will mostly vary a bit because of reflections, wrong direction it points to, for real colour correction just rent a box of filters, but for standard field work (one man crew) white balancing is the way to go, it would be impossible to change filters during a football game or something!
Bryan, An 18% gray card was recommended because it is at 50 IRE's. Flesh tones are supposedly at 75 IRE's and if one were to balance to a pure white they would not look as good as a balance to the 18% grey. Did you see the other thread I started about white balance and an XL-1? That is where I got the recommendation to use an 18% gray card. I ordered a couple from cameraworld.com but have not had a chance to try one out. Once I do I will be able to answer this question for myself. Maybe someone here whot has used a gray card can pipe in. I hope we haven't taken up too much of your time Bryan. Greg Matty |
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