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09-15-2009, 06:59 PM   #1
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Does WB temp setting get embedded in jpeg/exif?

Or is it in the RAW file only?

09-15-2009, 07:44 PM   #2
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Yes, the WB chosen by the camera is saved to the RAW file. It doesn't normally affect the RAW data itself, but it's recorded in the file, so when a RAW processing program displays your image, it uses that WB.
09-15-2009, 08:05 PM   #3
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WB Setting

The exif data in a jpeg does include the white balance setting used when the image was captured.

It is also included in the exif of a RAW file.

The difference is that the RAW data is more or less what comes directly from the sensor. The WB setting does not affect the image data directly. Whatever software is used to convert the RAW data into a displayable jpeg, tiff or whatever, uses that WB setting to do the conversion. This is true for both the in-camera jpeg creation and for post-processing using Photoshop or some other software on a computer.

When the RAW data is converted into a jpeg, whether in camera or on the computer, the WB data is combined with the RAW data to form the jpeg. At that point, the RAW data is discarded. IOW, the WB information is "cooked" into the jpeg.

This is one of the reasons that RAW files offer so much more flexibility in manipulating the data and correcting for errors. Did you have the WB set for fluorescent lights when you shot outside in bright sunlight? No problem, just tell Photoshop that it was really daylight. Voila! This is much harder to do with a jpeg, since the original RAW data is long gone.
09-15-2009, 09:45 PM   #4
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I only see the selected WB preset in the exif attached to the jpeg. Unlike in raw, the absolute color temp, in degK, isn't recorded. No big a deal if the WB preset was 'white fluoro' or 'shade' or some other fixed and tight range. But if it had been left at 'auto' instead, it's a broad range to pick from.

I use a driving sunglass in my car, those aviator type; a dark-tinted, reflective type in the winter against snow glare; and a small polarized one during the summer. The commuter trains I take daily have dark-tinted windows as well. I realized that my eyes haven't actually been exposed to unfiltered 'daylight' in a quite some time, and my brain is having trouble adjusting to WB.

09-16-2009, 10:28 AM   #5
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QuoteOriginally posted by wasim_altaf Quote
I only see the selected WB preset in the exif attached to the jpeg. Unlike in raw, the absolute color temp, in degK, isn't recorded.
It is - it *has* to be in order for RAW processing programs to work correctly. but it's not necessarily stored in any standardized place in the EXIF where you'd know how to find it. Could be somewhere in makernotes, or more likely within the completely proprietary part of the file. And it might not be reduced to something as simplistic as a single number for temperature - or even two numbers for temperature and tint. Light is far more complex than that; what you really want is a full spectrograph reading giving the relative proportions of each wavelength of light. And actually, I think something like that *is* included, at least for DNG. When working from DNG, RAW processing applications actually have to calculate temperature and tint numbers from that data, from what I have read. But that's the same data that the camera itself collects and works from, so it's not like the RAW processing program is missing information.
09-16-2009, 12:34 PM   #6
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QuoteOriginally posted by Marc Sabatella Quote
It is - it *has* to be in order for RAW processing programs to work correctly. but it's not necessarily stored in any standardized place in the EXIF where you'd know how to find it. Could be somewhere in makernotes, or more likely within the completely proprietary part of the file. And it might not be reduced to something as simplistic as a single number for temperature - or even two numbers for temperature and tint. Light is far more complex than that; what you really want is a full spectrograph reading giving the relative proportions of each wavelength of light. And actually, I think something like that *is* included, at least for DNG. When working from DNG, RAW processing applications actually have to calculate temperature and tint numbers from that data, from what I have read. But that's the same data that the camera itself collects and works from, so it's not like the RAW processing program is missing information.
OK, let's say I manually set a color temp, 6500k for instance, and the RAW processor will use that to adjust/correct whitebalance against that, before saving to jpeg or making it viewable on the screen. Most RAW software will show this manual/6500K as a camera setting for WB-type/color-temp. Now, if WB setting is left as 'auto,' which has a range of 4000k-8000k in k20d, then the camera makes a suggestion as to what color temp to be used by the RAW processor.

PPL/PBL don't display it at all from the raw file, showing only "auto" as WB-type. RawTherapee does show both, and I think so does Silkypix. For jpeg this can very easily be buried in the exif/metadata, as you've pointed out, or may be the format doesn't include it at all.
09-16-2009, 01:37 PM   #7
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First, I realize I misread your post. You are probably right with what you said previously - for JPEG, none of that stuff I mentioned is likely to be recorded (unless it happens to be recorded in the makernotes, which is possible). I was talking about RAW.

QuoteOriginally posted by wasim_altaf Quote
PPL/PBL don't display it at all from the raw file, showing only "auto" as WB-type.
That may be, but as the other programs demonstrate, the info *is* there - this is just one of the ways in which the PPL interface leaves a lot to be desired.

Note that sometimes you see a disagreement between programs as to what the selected temperature was, suggesting that the simple temperature/tint figures is not what is being used, but rather, the spectrograph-type data I mentioned, and different programs may calculate a temperature from that data differently. I've seen this for DNG but not for PEF (not that I've looked hard), which is what makes me think that with PEF, it really is the simple temperature/tint numbers being recorded and used.
09-17-2009, 12:54 PM   #8
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QuoteOriginally posted by Marc Sabatella Quote
Note that sometimes you see a disagreement between programs as to what the selected temperature was, suggesting that the simple temperature/tint figures is not what is being used, but rather, the spectrograph-type data I mentioned, and different programs may calculate a temperature from that data differently. I've seen this for DNG but not for PEF (not that I've looked hard), which is what makes me think that with PEF, it really is the simple temperature/tint numbers being recorded and used.
Thanks. I've been using PEF only. I should try out DNG and check it in RawTherapee. I'm not opposed to DNG, but it is ~50% larger -- 16M PEF compared to 24M DNG -- and the write speed appears longer than PEF (even after whatever compression is going on).

09-17-2009, 03:27 PM   #9
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DNG is larger when not compressed, but the compression options availabler for DNG can actually make it smaller than PEF. I think the K-7 ws the first Pentax camera to start compressing DNG files in camera, but the free Adobe DNG Converter can compress the DNG files produced by earlier cameras, or create compressed DNG files from the PEF files.

But really, it's the same basic RAW data either way, so unless you've got a real reason to change, I wouldn't bother. Main advantage of DNG is that metadata like IPTC keywords, also processing parameters form programs like Photoshop (ACR), Lightroom, ACDSee, and others can be stored directly with the file rather than requiring a sidecar XMP file.
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