White Balance on iPhone 4

vidguy7 wrote:

pberk wrote:
How would you expect the camera to know when you are taking an indoor photo?

That's what auto white balance does. The same mechanism is in all video cameras and most still cameras. It measures the color temperature of the lighting where you are and adjusts accordingly. If it didn't know the color temperature, your outdoor pix would look just as bad.

The fact that it can take pix outdoors with good white balance, shows the camera is capable of reasonably accurate colors.

That in fact is NOT how auto white balance works - what any camera needs to accurately calculate an auto white balance setting is a true white and/or a true black, which not all scenes have... and uses what it finds to adjust relative to a native white point that has been pre-defined. The native white point is what determines how warm or cool the whites in the photo will be rendered..

That is a different function from value readings which are gauging how light or dark a scene is and determine whether auto flash will fire.

Outdoors, you are generally working with a color rendition index of 100 - meaning that all colors in the visible spectrum can be seen. There is no artificial lighting (which is what I assume you are referring to when you say "indoors") which has a 100% color rendition index. Artificial sources skew towards one end of the spectrum or another. Incandescent lighting is warmer light, will accentuate the yellows oranges, reds, etc. Florescent lighting is a cooler source and will accentuate blues and greens. LED is a very very cool harsh light which can tend to flatten out colors and also creates a photo that is more sensitive to ambient reflected light - it is also the only type of light source that is cool enough (low power) to be used repeatedly on a phone camera without totally draining the battery.

I have gotten excellent indoor photos (of my white bulldog) with and without the flash with the iphone, with a very true white. On the other hand, I shot some photos with the phone at an event in a large light yellow room and except for the subject itself, which was lit directly by the LED and was captured with pretty accurate color, if somewhat overly vivid blues, the rest of the scene had a decidedly yellow cast as the color reflecting off the smooth walls (which are many times more reflective than an object with texture) was captured with greater sensitivity than you would appreciate with the naked eye.

All this to say that what the camera "sees" is not what the naked eye perceives - in a way the camera is much more sensitive than the naked eye, and that lighting conditions in a scene as well as the Light Reflectance Values of other colors present and the type of surfaces reflecting the light into the camera lens, will all play a role in how any camera "sees" color. This is a lot for even the most sophisticated cameras to handle, that's why for example,we bounce flash off a white ceiling, or diffuse it, rather than aiming it directly at a subject, etc.

I suspect that the native white point on the rear iphone camera was warmed up considerably to compensate for the very cool LED flash and that most of the indoor shots that are yellow are being taken under incandescent lighting, rather than the cooler, more energy efficient CFLs and the like.

With simple, inexpensive cameras that operate only in automatic modes, certain decisions have to be made by the manufacturer. They will not please all lighting situations. That doesn't mean that you can't take great pictures with them; it means that in order to do so you have to learn to see what the camera sees and compensate for it when composing your shot - or if you can't, use one of the many easily available and free or inexpensive post-production apps to adjust what you couldn't.

Let's put it this way, I've dealt with many many videocameras (which I use for work) and many digital still cameras as well as many phone cameras. The fact is the AWB of the I4 in TUNGSTEN lighting (that's what I referred to as 'indoor lighting') is much poorer than any camera, phone or otherwise I've ever used.

In fact, as has been pointed out, even Apple's shot of a couple under indoor lighting (color temperature of the lighting unknown) is too yellow. Also, most cameras do NOT need a pure white and a pure black to give you a good AWB. When using a MANUAL WHITE BALANCE setting, you DO need a white or 'gray card' to properly white balance. But AWB by design is not mandated to have a pure white object in the scene. In fact, if this were true, very few scenes would have proper colors with almost any camera.

Vidguy,

You missed my point.... I believe the camera was optimized for cooler light sources, NOT tungsten...

(Maybe I'm getting good indoor color rendition in my home is because I've gone green... replaced my incandescents with cool burning, energy efficient CFLS and other low energy sources...)

pberk wrote:

vidguy7 wrote:

pberk wrote:
How would you expect the camera to know when you are taking an indoor photo?

That's what auto white balance does. The same mechanism is in all video cameras and most still cameras. It measures the color temperature of the lighting where you are and adjusts accordingly. If it didn't know the color temperature, your outdoor pix would look just as bad.

The fact that it can take pix outdoors with good white balance, shows the camera is capable of reasonably accurate colors.

That in fact is NOT how auto white balance works - what any camera needs to accurately calculate an auto white balance setting is a true white and/or a true black, which not all scenes have... and uses what it finds to adjust relative to a native white point that has been pre-defined. The native white point is what determines how warm or cool the whites in the photo will be rendered..

Well to tell the truth that is pretty much how white balance works. The camera has no idea what is white or black until it knows something about the color temperature of the lighting. I have taken photos with the iP4 of a T8 Color Target under three different lighting 5500K (More or less outside on a sunny day) 3200K (My Modeling Lights) and 2500K (40 watt incandescent bulbs) and found the camera works well until you get around 2500K. That's when things fall apart. I did the same thing with my 3GS and it also fell off around 2500K but not as bad. My guess is they are using the same algorithm as used in the 3GS and an update should fix this issue.

I'm sure your white Bulldog show just as yellow if shot under the 2500K lighting.

I am a professional Photographer for over 25 years and work with these issues on a daily basses.

Tom

Message was edited by: tomh1000

Message was edited by: tomh1000

I don't think so. Cameras do not measure temperature (which is a heat measurement), they base their algorithms on reflected light, not hear....

I also work ;with these issues everyday..as a lighting designer and color specialist

A properly functioning AWB should not need to be 'optimized' for any particular kind of lighting. This is true when the flash is being used too. An AWB circuit should recognize the color temperature of the flash and set the proper color rendition when it's being used.

Any AWB that's already 'biased' for a particular kind of lighting, will not effectively work in other kinds of lighting. However, with that said, I do believe a software fix is not that difficult to address this issue that most are having under traditional tungsten lighting.

Tom, you and I have the same understanding and experience. My experience is more on the video end where I work professionally. But as you know, color temperature is color temperature whether it's video or stills.

You do not understand the meaning of color 'temperature'. It is NOT the same thing as the air temperature. Color temperature is a very common term used in photography and video and can be found in virtually any manual from a still camera to a video camera.

Colour temperatures are based on the radiation of a "black body" object so in those cases, yes they are based initially on the temperature of the object in degrees Kelvin.
However, the actual temperature in Kelvin of a light sourse has nothing to do with it's colour temperature as it can be modified using dyes and phosphors etc. such as in flourescent lighting.
The gas temperature remains the same inside the tube but the phosphor coating on the inside of the tube can be modified using varying amounts of red, blue and gree, to make the colour temperature of the light "warmer" or "cooler" which actually should be termed as "lower" or "higher" to avoid confusion.

A camera should be able to "average" out a scene and adjust it's response to neutralise any strong colour biases.
In indoor lighting which has a very low colour temperature, even expensive DSLRs struggle on Automatic and for this reason, there are usually selectable white balance presets built in, as a minum requirement

At the very least I think we should be able to have selectable presets incorporated in the iPhone as Auto White Balance is inherently unreliable and an "uneducated" guess at best.
Take for instance a beautiful red sunset. If left to its own devices, an auto white balance system would try to neutralise the red colour cast and therfore would ruin the entire shot.
You would set the camera to "daylight" in order to maintain the redness when you want to. You shouldn't have to rely on an electronic system enterpreting the scene you're about to capture, because it has no idea what it is and what you're trying to achieve.
Indoor, flourescent, sunny, cloudy, shady and flash is what's required.
That shouldn't be too difficult for Apple or a 3rd party to come up with, now should it?

YOU do not understand what color temperature is.... it is not just a "term" or a label someone came up with for photography... Color temperature is an actual measurement of heat as determine by the temperature at which a particular hue in the spectrum will radiate from a black body as measured on a Kelvin scale. Cameras do not measure color temperature... they use known color temperatures in functions such as AWB to chromatically adapt the scene to the pre-set "film sensitivity" (or in electronic devices to a native white point)... If the native white point of the "film" is set to equal the temperature of tungsten lighting, then the yellowish light of that light source will appear white in the photograph. Chromatic adaptation algorithms are generalized, not specific to every color, and designed to correctly render neutrals and achromatics relative to the native white point. Not every area of a photograph receives equal light, especially when a static flash is used, so it stands to reason that the algorithm will not perfectly correct all areas of the photograph which will be particular evident when shooting with a flash indoors.

Dave Hutch wrote:

That shouldn't be too difficult for Apple or a 3rd party to come up with, now should it?

You've got to be kidding...not too difficult? In the old days, you took a photograph, controlled what film you used and what paper you printed on. You had virtually total control over your end result.

Today we take digital photos, print via machines which each have their own color profiles or display on screens with varying white points... and you think it would be easy to create an algorithm that
just works in all digital situations??? [ICC profiles are all about trying to get colors to match across devices]. There are a number of methods out there used in chromatic adaption algorithms, but the industry has never stopped debating which is the best way to go...

Whomever comes up with a perfect (or even much improved) algorithm will indeed become a very rich man, or woman...

adobe's version is free. i'll check out
photogene when i get the chance though!

agreed, we shouldn't have to be correcting
pics taken with the ip4. that's why it's
always a last resort for me with indoor shots.

Yes I do understand what color temperature is, I do video for a living. You have two people on this thread that do this professionally, but you know better. However, your nasty attitude makes a real discussion difficult. I find too many with attitudes like yours on this site. Too bad, it really stifles the exchange of information. I've never seen so many pompous attitudes at one location.

This just isn't important enough to waste any more time.

Message was edited by: vidguy7

I shoot AWB on a Canon 1DMK4 and use to do it with a 1DsMK3 and still make WB adjustments in postprocessing all the time. I either shoot AWB and adjust or set it using a variety of techniques in the field. Either way there are adjustments. So, no way do I expect any device's AWB to get it "right" under all conditions. Also, what some people see as the correct WB for a given image others will see it is off. My experience with my iP4 is that does better outdoors than indoors which is typical of most AWB functions.

This is a phone camera and I"m amazed that it can complete with your basic Point and Shoot.

it seems the problem is worse under fluorescnet lighting. I take photos of my patients in my office that has fluorsecent lighting and the skin tones all come out way too green. i hope there is a fix to this, otherwise this phone will not be as usefult to me.

the white balance seems fine for outdoor shots where the color temperature is a lot different.