How Does HMC40 Use ATW to Adjust Color Balance?

D

Denniscasey

Well-known member
I am reading "How Digital Photography Works" 2nd Edition by Ron White which explains how digital cameras work (mostly still cameras). Discussing automatic white balance in Canon still camera it says quoting: "The cameras software notes the ratio of red to blue pixels (green does not have a significant effect on white balance). If the ratio does not match the usual proportions of red and blue for a white object in normal daylight, the camera's processor adds more red or blue pixels to the image to correct the color. Subsequently, when a photo is snapped, the processor makes the same red/blue adjustments to it." end quote

1. Is that how the HMC40 works when one relies on ATW (Automatic Tracking White)--idoes it look at scene and adjust ratio of red/blue to try to get "normal" daylight ratio?

2. If a white object is not available in the scene you are shooting, does the HMC40 ATW still just adjust the ratio of red/blue pixels?3. Looking just at outdoor shooting, what conditions are most likely to "fool" ATW and give strange color? For instance, early on in my learning I noticed panning from a sunlit scene to a shady scene could give a color shift.

The context of my questions is I shoot primarily outdoor scenes or sporting events. Light can change frequently (cloudy, sunny, etc) and light where I am standing may not be same as scene I am shooting (I am in shade, scene is in full sun for example). So I find ATW and ATW Lock can sometimes give me a better representation of scenes color (or color temperature) than if I do manual white balance where I am standing. So, I would like to know how HMC40 applies ATW so I can better understand when to use it and when not to use it (or just set camera to 5.6 K). Compounding my concerns is fact that neither viewfinder nor LCD can be relied on to represent colors (as many have noted) so while I am recording scene I don't really know exactly what I am capturing.I have already received a lot of good help/advice from members of this forum on this white balance topic and this post continues my quest to better understand white balancing (theory, practical application with HMC40). Dennis
 
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Hey Dennis

I'll leave Barry to answer the red and blue pixel question but yes, the HMC40 (well I know my 82's do this) will give a cast if there is a very dominant colour in the room...I shot a Realty home the other day and all the walls were shocking pink...the door was white but it looked quite pink in the video. Did you also know that you can "help" the ATW?? Leave the WB in auto and just zoom into anything white ...even a piece of white paper or white cloth and if you watch the LCD/EVF you will see that the camera will correct itself after 10 -15 seconds ...I use that all the time especially in an enviroment with lots of greenery or outdoors with dominant flower colour. Yep, you will fool the camera at sunride and sunset if everything is very orange but simply do a manual WB or just help the ATW with something white and you will find the colour is always accurate..I have never had to colour correct a wedding the bride's dress and bridesmaid's dresses always turn out perfect and that's all on ATW (but I always still use a white cloth to help it set a reference. BTW: Never judge anything purple on your LCD!! For some reason LCD's show purple objects as blue (probably again a red/blue mix issue) I found that girls wearing purple dresses look blue in the LCD or EVF but on the footage the colour is pefect!!


Chris
 
Hi Chris, Thank you for sharing "real world" experience. As I experiment more with shooting video and using HMC40 I become more aware of things that are evident to experienced users. My current priority is the "quality" of light and how the HMC40 captures it--for instance the nuances of light quality at sunrise/sunset.

There are many instances where I find the method you mention (let ATW adjust to a white object and then I use ATW LOCK) captures quality of light better than doing a manual white balance. As I have mentioned in past, it seems to me that manual white balance works best in a studio setting or outdoors where you can have the subject hold the white balance card so it is in the same light as subject is---often not possible when distant scenery outdoors is in different light than where you are standing. In that circumstance I think the ATW "method" works best.

To put following in perspective, I don't have a problem with color cast in most of my videos (not my skill, just good lighting conditions). However, as a novice without the experienced "eye" of professionals I am frustrated by inaccuracies you also mention in color rendition of LCD/EVF (not just HMC40 problem I am sure). For instance, yesterday I was experimenting filming fall colors in the morning with overcast sky about one hour after sunrise. Sun was behind clouds behind me, but scene in front was patch of brilliant blue sky with white clouds and subject (leaves on trees) in foreground. I did manual white balance with card propped up in front of me and every time I did that the "blue" sky and white clouds looked gray through EVF (I tried white balance several times). Then I set white balance to 5.6K and blue sky and white clouds looked more like actual colors through EVF. Then I pointed camera at blue sky with ATW on, gave it time to adjust, but through EVF sky did not look brilliant blue it actually was. I was frustrated by not being able to white balance to "see" brilliant blue sky through EVF: but as you mention, when I viewed all my experiments on TV the sky generally looked blue in all cases--never did have the gray cast I was seeing through EVF in several cases. Hard to discern differences I was seeing through EVF.

I have bought a 5 inch external LCD monitor which has blue gun and other features which I hope will give more accurate color rendition when I have calibrated it. However, when I read Barry Green's comments on pages 16-17 of "The HMC Book" about the need for almost constant calibration of external monitors then it may only give me a better "indication" and not accurate color representation. Regards, Dennis
 
I mostly agree with Chris about using atw on the hmc40. Though I'm not a fan of auto cam features in general, I must admit all the auto features on the 40 work pretty well. Doing a manual balance to a white card is the best, though using atw and locking it in works well enough for most situations unless you are doing critical work which requires more care. And don't forget to do a black balance also!

Grant
 
Dennis,

Under the difficult circumstances you describe, judging color from a small monitor is difficult at best and unless you buy a monitor as expensive as the cam, judging color is pretty futile. Remember that what you see on any field monitor is likely to look different than on your editing suite and will change again when viewed on a TV. For sure, the HMC40 VF and flipout are the weakest part of a great little cam. Over time, I've become ok with the focus features, but color, not a chance. But I wouldn't try to judge color in any other prosumer cam either. I do use an external anytime I can.

When shooting vivid sunsets, instead of balancing your cam with light coming over your shoulder, looking at the sunset, turn around and balance your white card with the light coming FROM the sunset. Also remember that as the light fades, WB will become much more difficult. You might also consider experimenting with your scene file to get the desired effect.

Grant
 
ggrantly said:
Dennis,

Under the difficult circumstances you describe, judging color from a small monitor is difficult at best and unless you buy a monitor as expensive as the cam, judging color is pretty futile. Remember that what you see on any field monitor is likely to look different than on your editing suite and will change again when viewed on a TV. For sure, the HMC40 VF and flipout are the weakest part of a great little cam. Over time, I've become ok with the focus features, but color, not a chance. But I wouldn't try to judge color in any other prosumer cam either. I do use an external anytime I can.

When shooting vivid sunsets, instead of balancing your cam with light coming over your shoulder, looking at the sunset, turn around and balance your white card with the light coming FROM the sunset. Also remember that as the light fades, WB will become much more difficult. You might also consider experimenting with your scene file to get the desired effect.

Grant
Click to expand...

Grant, all good points and the one about turning around to white balance on light coming FROM the sunset sounds so logical after you pointed that out, but I hadn't tried it. I will use that tip quite a bit I expect. Regards, Dennis
 
Thanks Grant

I forgot to mention the Black Balance too...It was in my mind but then I never added it!! Dennis, do you know how to do a black balance??? It's a good idea to do a black balance every few months!!

Chris
 
ChrisHarding said:
Thanks Grant

I forgot to mention the Black Balance too...It was in my mind but then I never added it!! Dennis, do you know how to do a black balance??? It's a good idea to do a black balance every few months!!

Chris
Click to expand...

Chris, I did learn how to do black balance. I had asked about that in an earlier post (including asking about doing that while camera was in full auto) and Barry replied:Quote: "Just hold the white balance button in longer, until the "ABB" process starts. You don't need to leave the lens cap on, the camera has an internal iris that it shuts to completely block all light. You don't have to do it while the camera is in auto, it's just that it's possible to do it in auto just like it's possible to do it in manual." end quote.

Per my thread starter, I would still like to understand technology of how HMC40 does ATW particularly in cases where there is no white object in scene (does it look at ratio of blue/red pixels and "force" camera to conform to ratio you would see in normal daylight). Just would help me understand how HMC40 designers tried to teach camera to interpret/adjust what it sees. Dennis
 
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