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11-11-2009, 09:16 PM   #31
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QuoteOriginally posted by BB_Zone28 Quote
........ However, the fixed setting "preset values" would still make sense to have some consistency as I discussed in previous postings above.
One example being that Fixed WB is quite important during Video capture.
A video where the WB changes halfway through really doesn't look good. Normally you just want the WB to stay the same if the lighting conditions change halfway.

11-12-2009, 11:15 AM   #32
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QuoteOriginally posted by jeffkrol Quote
Because they want a different look, predominantly for skin tones would be my guess..5200 being "warmer" then 5500K.
I seem to remember something about the temp is more flattering to Asian skintones.. or was it European? Camera makers DON'T even standardize iso, nor f stops either. They pretend to.
Lenses are not even exactly as stated in f stop nor focal length...
The old lens tests used to state the REAL focal length and real f/stop based on measurements of their own.
exposure meters can be the worst and don't even go into the tone curves (which are always different in each camera.
Adding slight warmth to skin tones is generally considered flattering. Where standardized WB presets can be useful is when you use a flashgun rated at 5500k (very common for Xenon arc tubes in shoe mount external flashes) with a camera that uses 5400k CT for its flash WB setting that it can add a very slight coolness instead of warmth. Another cameras uses 5600k CT for its flash WB setting and that results in a slight warmth being added which I prefer to the coolness. It's slight, but you can definitely see it on white objects in images compared side by side.
However, if the WB preset CT is just a starting point (vs. fixed setting), then presumably the camera makes an accurate evaluation of the light source and corrects the WB values accordingly.


Granted, specifications have production "tolerances" so there's going to be some "slop" in what's listed and the actual measure value. Although, I understand the ISO can be WAY off. I've read some tests about that from a link from DP Review a while back.
With f/# they at least use the historic full EV values ... 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22 etc. while they may differ slightly on the 1/3 EV in-between settings. (and I'm aware that f/11 is technically closer to 11.3 and f/22 to 22.6 which explains f/45)




QuoteOriginally posted by jeffkrol Quote
I assume they will get just as confused if they had the exact same K temp yet each photo w/ different cameras looked "different" which would probably happen..

At least they all would have consistent initial settings!!
It would also tell you if the "claimed value" was very accurate because if everyone uses the same CT values and some are warm and others are cool, then someone isn't very accurate in their claims!!!
Hmmm, makes me wonder if the reason for variability in usage of numbers and use of the word "about" prefacing stated CT values could possibly imply the values aren't measured very accurately or that maybe they aren't even measured at all??? Maybe they're based on a standard set of "accepted" assumptions during the design phase and/or just quickly checked with non NIST traceable sources??? If so, then approximate claims would be made because the initial assumptions/methods are approximate???? If so, that would explain why their isn't more consistency and to press this issue further would only lead to added cost in the design and prototyping phase due to yet another set of measurements that would have to be precisely/accurately made that adds even more cost to development and production. I can appreciate that since I've used calibrated "standard" black body radiation sources to measure and calibrate optical pyrometers.



QuoteOriginally posted by jeffkrol Quote
As stated earlier daylight is defined between 5000-6500K, none would be incorrect and to pick 1 that all camera makers use would be like getting them to be all the same RAW format... and my favorite quote which can be universally applied across the board..
I think teaching them to learn their camera is more important then the K scale...
I'm not sure the RAW standardization compares...sensors are unique. But the idea of DNG format is catching on among some camera makers. It's a choice to make about "processing" the data before writing to the memory card. And even though Adobe proposed DNG, they cash in on the fact that most camera makers won't use DNG and Adobe doesn't support the newest cameras produced that only use non DNG RAW files beyond their current version of Photoshop.

TIME is defined in units of seconds (like CT uses Kelvin) and exposures can vary from very short to very long. So, is it wrong that most cameras use 1/125, 1/250, 1/500 etc. as preset values for shutter speed because exposures can be all over the place depending on the amount of light? (just like CT depending on the time of day) Yet if you measure the actual shutter speed it may be off from the stated value. So again, based on your argument, why should shutter speed values even be standardized between cameras? You could pick and use any number you want as the "preset" choices in the camera.
I'm just saying why can't cameras assign their "icon" presets like Flash=5600k, "Daylight=5500k" etc. so they're consistent like other parameters have already been made to be. Sure, depending on what time of day the CT value changes, but they had to pick some value to assign to those preset values. So why not make them consistent instead of arbitrary???

Teaching about CT Kelvin is useful to understand how to use your camera. It aids in your choice of using "preset" WB settings or "custom" WB.



QuoteOriginally posted by jeffkrol Quote
'The exposure meter is calibrated to some clearly defined standards and the user needs to adjust his working method and his subject matter to these values. It does not help to suppose all kinds of assumptions that do not exist.'
Erwin Puts
Now, I even agree that we don't need standard on "meter patterns" inside of cameras. Only that whatever pattern is used, that if you meter on an 18% gray card it would yield the same exposure from camera to camera.

Presumably they claim 18% gray for the meter calibration. However, Ansel Adams' use of the Zone system discovered that the actual method doesn't exactly yield that claimed result. He made efforts to encourage the camera and meter makers to be more accurate to their claimed values.

Thanks again for your responses!

Last edited by BB_Zone28; 11-13-2009 at 10:53 AM.
11-12-2009, 11:24 AM   #33
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QuoteOriginally posted by kittykat46 Quote
One example being that Fixed WB is quite important during Video capture.
A video where the WB changes halfway through really doesn't look good. Normally you just want the WB to stay the same if the lighting conditions change halfway.
My sentiments concur!
11-12-2009, 12:17 PM   #34
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Something else that hasn't been considered in this discussion of why assigned "preset" Color Temperature (CT) values for White Balance (WB) "icons" in digital cameras are listed as approximate...

the camera lenses!!!!

How much does the spectral transmittance of one design of lens vary from another? Some use specialized glasses to deal with design aspects. Add to that the fact that many people add a filter on the front that can shift the CT of the optical image formed on the digital sensor by a slight amount. Also, older lenses have coatings that may age and potentially affect spectral transmittance, (esp. if used in tobacco filled environments) plus the choice of multiple optical coatings methods on new lenses may have a few spectral dips that slightly alter spectral transmittance and thereby the overall balance of colors. All those little things can add up to theoretically make WB appear slightly different between different types of lenses.
So that would provide another reason why stated values are approximate and that you ultimately have to rely on the camera to use a starting point and make final corrections automatically to the WB.

11-12-2009, 12:59 PM   #35
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QuoteOriginally posted by BB_Zone28 Quote

Now, I even agree that we don't need standard on "meter patterns" inside of cameras. Only that whatever pattern is used, that if you meter on an 18% gray card it would yield the same exposure from camera to camera.

Presumably they claim 18% gray for the meter calibration. However, Ansel Adams' use of the Zone system discovered that the actual method doesn't exactly yield that claimed result. He made efforts to encourage the camera and meter makers to be more accurate to their claimed values.

Thanks again for your responses!
All assumptions on metering get thrown out when using Matrix metering.
Nikon uses a LUT of something like 10,000 entries to match the Matrix w/ assumed scenarios.. They may render a grey card filling the screen the same but after that all bets are off. CW metering has much the same problem only greatly reduced.
About the only "consistent" metering procedure would be w/ spot metering..
as to 18% there was always a fudge factor built in which made the very expensive spot meters vary from each other. ISO you would think is the most standardized parameter....:
Chasing a Gray Cat In a Gray Room: the level of middle gray and the headroom in the highlights for Canon 5D Mark II | LibRaw
This approach, with all its simplicity, is in fact based on the properties of the RAW converter and on the transformations it applies to RAW data. In particular, the converter can introduce hidden exposure compensation, change the tone curve, and so on. The sensitivity of the camera resulting from such a procedure is a pretty arbitrary value.
Film speed - Wikipedia, the free encyclopedia
The Recommended Exposure Index (REI) technique, new in the 2006 version of the standard, allows the manufacturer to specify a camera model’s EI choices arbitrarily. The choices are based solely on the manufacturer’s opinion of what EI values produce well-exposed sRGB images at the various sensor sensitivity settings. This is the only technique available under the standard for output formats that are not in the sRGB color space. This is also the only technique available under the standard when multi-zone metering (also called pattern metering) is used.,,,,,,,,,,,,,Despite these detailed standard definitions, cameras typically do not clearly indicate whether the user "ISO" setting refers to the noise-based speed, saturation-based speed, or the specified output sensitivity, or even some made-up number for marketing purposes.,
As I said it's all smoke and mirrors....
As to 18%..........
http://www.libraw.org/articles/zone-v-in-digital.html
So, in the perfect world of a spot-meter calibrated to ISO standard and pure gamma = 2.2 transform of perfectly linear data coming from the sensor, the neutral surface should render 101 RGB if exposed according to the spot-meter;
Orig Pentax D had behavior close to this...
Current ISO standard, however, recommends that the metering calibration point is less then 18% by half a stop to increase the room in the highlights. The standard suggests 18%/SQRT(12)=12.73%. Adding the slack the standard allows the total headroom is somewhat less then 3 stops, 2.97 eV.
and from the Wiki article:
The factor 78 is chosen such that exposure settings based on a standard light meter and an 18-percent reflective surface will result in an image with a grey level of 18%/√2 = 12.7% of saturation. The factor √2 indicates that there is half a stop of headroom to deal with specular reflections that would appear brighter than a 100% reflecting white surface.

A nice primer on white balance/color temp. mostly for my own reference:
http://www.ronbigelow.com/articles/white/white_balance.htm

Last edited by jeffkrol; 11-12-2009 at 07:21 PM.
11-13-2009, 11:04 AM   #36
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QuoteOriginally posted by jeffkrol Quote
All assumptions on metering get thrown out when using Matrix metering.
Nikon uses a LUT of something like 10,000 entries to match the Matrix w/ assumed scenarios.. They may render a grey card filling the screen the same but after that all bets are off. CW metering has much the same problem only greatly reduced.
About the only "consistent" metering procedure would be w/ spot metering..
as to 18% there was always a fudge factor built in which made the very expensive spot meters vary from each other. ISO you would think is the most standardized parameter....:
Chasing a Gray Cat In a Gray Room: the level of middle gray and the headroom in the highlights for Canon 5D Mark II | LibRaw
This approach, with all its simplicity, is in fact based on the properties of the RAW converter and on the transformations it applies to RAW data. In particular, the converter can introduce hidden exposure compensation, change the tone curve, and so on. The sensitivity of the camera resulting from such a procedure is a pretty arbitrary value.
Film speed - Wikipedia, the free encyclopedia
The Recommended Exposure Index (REI) technique, new in the 2006 version of the standard, allows the manufacturer to specify a camera model’s EI choices arbitrarily. The choices are based solely on the manufacturer’s opinion of what EI values produce well-exposed sRGB images at the various sensor sensitivity settings. This is the only technique available under the standard for output formats that are not in the sRGB color space. This is also the only technique available under the standard when multi-zone metering (also called pattern metering) is used.,,,,,,,,,,,,,Despite these detailed standard definitions, cameras typically do not clearly indicate whether the user "ISO" setting refers to the noise-based speed, saturation-based speed, or the specified output sensitivity, or even some made-up number for marketing purposes.,
As I said it's all smoke and mirrors....
As to 18%..........
Headroom in Highlights : Where is Zone V in The Digital World? | LibRaw
So, in the perfect world of a spot-meter calibrated to ISO standard and pure gamma = 2.2 transform of perfectly linear data coming from the sensor, the neutral surface should render 101 RGB if exposed according to the spot-meter;
Orig Pentax D had behavior close to this...
Current ISO standard, however, recommends that the metering calibration point is less then 18% by half a stop to increase the room in the highlights. The standard suggests 18%/SQRT(12)=12.73%. Adding the slack the standard allows the total headroom is somewhat less then 3 stops, 2.97 eV.
and from the Wiki article:
The factor 78 is chosen such that exposure settings based on a standard light meter and an 18-percent reflective surface will result in an image with a grey level of 18%/√2 = 12.7% of saturation. The factor √2 indicates that there is half a stop of headroom to deal with specular reflections that would appear brighter than a 100% reflecting white surface.

A nice primer on white balance/color temp. mostly for my own reference:
White Balance
The whole 18% gray card and light meter topic could fill pages of discussion! I've seen several digital cameras meters that default to underexposure when applying Zone system techniques. I guess I could blame it on 18%/√2 headroom protection. Thanks for the links, I'll have to review them as time permits.
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