How to determine what color temperature was used to develop an image?

[aajax]

The subject question pretty directly raises another much more basic question which is "what reference information does Canon provide regarding the metadata produced by Canon cameras and software (e.g., DPP)?".

A basic experiment that I've undertaken is to open a raw image file in DPP4 and then adjust the White Balance by changing the "Color Temperature".  Then the raw file is "Converted and saved" (some might call that developed) in a standard image format (e.g., in this case 16bit .tif).  When I examine the metadata (using ExifTool/ExifToolGUI) I cannot find anything in the .tif file that indicates what "Color Temperature" was used by DPP4 to develop said image.  Isn't this something that should be possible?

The metadata item referred to as "Color Temperature" says 5200 in both the raw and .tif file.  Hasn't this been changed?

From some research I've done on White Balance I think it is accurate to say that "Color Temperature" is NOT a property of the raw data.  Rather, the process of developing the raw data into an image (file) involves the application of color temperature.  Of course color temperature is a property that the camera must assign in order to develop the raw data and create an image (i.e., .jpg) file.  I have the idea that this might be a lot more complicated that anything I've yet learned but it does seem like I should be able to determine what value was used for that property.

It is also my understanding that DPP4 attempts/intends to mimic what the camera would do as the starting point for transforming the raw data into something that can be viewed as an image on the computer's display.  In my case, the White Balance tool always defaults to something called "Auto: Ambience Priority".  Whenever, this selection is changed to "Color Temperature" the value is set to 5200 (i.e., same as the metadata).  However, this selection does normally produce some change in the appearance of the image which suggests that 5200 was NOT the value used when "Auto: Ambience Priority" was selected.  I think what I'd like to be able to figure out is what temperature value corresponds to the image I'm looking at.  Right now I assume that if I switch to "Color Temperature" mode and select a value for temperature that would be it.  However, I haven't figured out how to tell what it is from the image file (e.g., .jpg or .tif) created by the development process.

It might be worth mentioning that other image editing software that I've tried suffers from the same problem!

[Waddizzle]

Let’s start from the beginning.  What is metadata?  Metadata is data that describes data.  For example, metadata that would describe a Social Security Number might look like this “ ### - ## - #### “, which describes the format of the SSI number.

Much of the metadata stored with a photograph describe how the image should be displayed.  White Balance is not “part of the image” with a RAW or TIFF file.  Usually, the WB metadata describes the camera’s WB setting when the photo was captured.

[aajax]

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@Waddizzle wrote:

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Much of the metadata stored with a photograph describe how the image should be displayed.  White Balance is not “part of the image” with a RAW or TIFF file.  Usually, the WB metadata describes the camera’s WB setting when the photo was captured.

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I'm a bit new at this which might mean that I'm not as familiar with the lingo that more experienced people might use.

However, it is my understanding that in order to process the raw data into a form that can be viewed on a display device of some kind as an image/picture (i.e., development) a color temperature which represents a source of light is applied.  The White Balance control on the software used to process the raw data allows the user to choose whatever temperature they would like.  To my way of thinking about it, once this is done and the resulting image is rendered into a standard format such as TIFF the resulting image (file) could be characterized as having a Color Temperature equal to whatever value was selected by user when developing the raw data.  That is what I was hoping could be determined by examination of the image file.

When the raw data is developed by the camera it must, likewise, select and apply a color temperature.  The experiments I've performed appear to me to suggest that the metadata item called Color Temperature included in the Makernotes for my Canon camera is NOT the value that was used to produce the initial image that DPP displays when it is opened for editing.  This is based on my observation that if I apply that value using the DPP White Balance tool the image changes.

I am aware of another complication that arises when using image editing software.  Some such software, for example GIMP and Rawtherapee, allows the equivalent White Balance tool to be applied to an image that has already been developed.  In that, when a .jpg or .tif file is opened for editing.  From other research I've done it has been determined that those programs have no way of knowing the answer to my question and they essentially assign a value of their choosing. They then allow the user to apply the White Balance tool as if that were the known value meaning they are essentially either increasing or decreasing the temperature from an unknown value.  This pretty much has the effect of producing an image where the value I'm trying to determine has in fact been lost.

It seems like DPP has chosen a different course.  DPP disables the White Balance tool and prohibits it from being applied when editing a .jpg or .tif file that has already been developed (i.e., raw processing completed).  My inclination is to suspect that the standards for .jpg and .tif do not provide a means for keeping track of color temperature.  To this extent I also think that DPP has made the best choice.  While use of the white balance tool can be desirable when editing a standard format image file for the purpose of producing special/artistic affect, rather than faithful depiction of the scene, it would be better if the tool were called something else in order to avoid confusing such an operation with what is done when choosing a color temperature for developing a raw file. In that, white balance cannot truly be adjusted when the software has no idea what color temperature was used to develop the corresponding raw data.

However, open source developers who are indifferent to the source of the image being opened for editing purposes are confronted with a different situation than Canon who is supplying software for editing images produced by Canon cameras.  I would expect open source developers to stay focused on the standards whereas Canon has the opportunity to add proprietary capability for its' customers.  In fact, Lens Correction is one such feature supported by DPP.  I'm guilty of imagining that the same could apply to my question and was hoping someone might know that it had as well as how to figure it out.

Following is a portion of the Makernotes for an image I've been experimenting with which seems to have the data pertaining to White Balance (Color Temperature).  If what I'm looking for is there I haven't figured out where.  If it is there I'd be grateful for someone to explain.  If it is not the simple answer to my question may be that such a color temperature cannot be determined from the image file after an image has been developed.

WB Shift AB                     : 0
WB Shift GM                     : 0
Measured RGGB                   : 496 1024 1024 604
Color Space                     : sRGB
Sensor Width                    : 5344
Sensor Height                   : 3516
Sensor Left Border              : 152
Sensor Top Border               : 56
Sensor Right Border             : 5335
Sensor Bottom Border            : 3511
Black Mask Left Border          : 0
Black Mask Top Border           : 0
Black Mask Right Border         : 0
Black Mask Bottom Border        : 0
Color Data Version              : 14 (1300D)
WB RGGB Levels As Shot          : 2140 1024 1024 1636
Color Temp As Shot              : 4960
WB RGGB Levels Auto             : 2140 1024 1024 1636
Color Temp Auto                 : 4960
WB RGGB Levels Measured         : 2140 1024 1024 1636
Color Temp Measured             : 4960
WB RGGB Levels Daylight         : 2106 1024 1024 1526
Color Temp Daylight             : 5200
WB RGGB Levels Shade            : 2427 1024 1024 1301
Color Temp Shade                : 7000
WB RGGB Levels Cloudy           : 2265 1024 1024 1406
Color Temp Cloudy               : 6000
WB RGGB Levels Tungsten         : 1524 1024 1024 2284
Color Temp Tungsten             : 3200
WB RGGB Levels Fluorescent      : 1846 1024 1024 2166
Color Temp Fluorescent          : 3729
WB RGGB Levels Kelvin           : 2106 1024 1024 1526
Color Temp Kelvin               : 5200
WB RGGB Levels Flash            : 2351 1024 1024 1387
Color Temp Flash                : 6303
Average Black Level             : 2046 2046 2046 2046
Per Channel Black Level         : 2045 2045 2046 2046
Normal White Level              : 11767
Specular White Level            : 12279

[RobertTheFat]

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@aajax wrote:

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@Waddizzle wrote:

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Much of the metadata stored with a photograph describe how the image should be displayed.  White Balance is not “part of the image” with a RAW or TIFF file.  Usually, the WB metadata describes the camera’s WB setting when the photo was captured.

---

I'm a bit new at this which might mean that I'm not as familiar with the lingo that more experienced people might use.

However, it is my understanding that in order to process the raw data into a form that can be viewed on a display device of some kind as an image/picture (i.e., development) a color temperature which represents a source of light is applied.  The White Balance control on the software used to process the raw data allows the user to choose whatever temperature they would like.  To my way of thinking about it, once this is done and the resulting image is rendered into a standard format such as TIFF the resulting image (file) could be characterized as having a Color Temperature equal to whatever value was selected by user when developing the raw data.  That is what I was hoping could be determined by examination of the image file. ...

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It may help your understanding to keep in mind that color temperature is a characteristic not of the image, but of the ambient light that was used to create the image. So if in, say, DPP, you set the color temperature higher (bluer), the image will be made to appear redder; and if you set it lower (redder), the image will be made to appear bluer. It sounds counterintuitive, but isn't if you think it through.

[aajax]

I've played with the WB adjustment tools in various image editing programs and found them to be very useful. While they are often described in the context of making the image accurately portray the original scene I've found them just as useful for distorting the scene to achieve what I think could be called artistic affect.

Your point about the distinction between ambient light and image fits my understanding so long as by image you are referring to is the raw data. That ambient light must be factored in to produce something can be displayed for our eyes to see. Dispensing with all of this technical jargon I think it would be fair to say that absent light there is no image. In that, even without cameras there is a pretty strong relationship between these 2 factors.

[Waddizzle]

“However, it is my understanding that in order to process the raw data into a form that can be viewed on a display device of some kind as an image/picture (i.e., development) a color temperature which represents a source of light is applied.  The White Balance control on the software used to process the raw data allows the user to choose whatever temperature they would like.  To my way of thinking about it, once this is done and the resulting image is rendered into a standard format such as TIFF the resulting image (file) could be characterized as having a Color Temperature equal to whatever value was selected by user when developing the raw data.  That is what I was hoping could be determined by examination of the image file.”

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You are making a major false assumption.  You are assuming that every JPG should have WB data because it originated from a photograph, which is not the case.  A JPG file is not always created from a photograph.  This is why JPG files do not contain certain types of metadata, such as WB.

[aajax]

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@Waddizzle wrote:
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You are making a major false assumption.  You are assuming that every JPG should have WB data because it originated from a photograph, which is not the case.  A JPG file is not always created from a photograph.  This is why JPG files do not contain certain types of metadata, such as WB.

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I think this is the point I was trying to make when I said, "My inclination is to suspect that the standards for .jpg and .tif do not provide a means for keeping track of color temperature.".  I admit feeling the need to waffle a bit because I'm by no means an authority on these standards.  At the same time I do know for a fact that some digital image editing software, other than DPP, does allow the White Balance tool to be applied to any .jpg whether photograph or not.  This is why the idea that even though the algorithm/s involved can be applied equally well it ought to be called something else when dealing with images that aren't known to be photographs and where a temperature can be associated with the current state of the image data.  The only way that this processing could possibly be considered White Balance is if a color temperature can be accurately associated with the current state of the image data (i.e., prior to making temperature adjustments).

My inquiry was provoked in part because it appears to me that GIMP has changed in such a way that, I think, it may be doing what I've described.  Therefore, I should probably point out that this is not my idea but rather what I presently think is the motive behind the GIMP change.  Insofar as GIMP does not process raw files they are stuck with the need to do whatever they are going to do on what I'm referring to as standard image formats (i.e., jpg, tif, png, etc.) none of which need to be photographs.  GIMP, by the way, does not use the term "White Balance" which to my way of seeing it is correct and possibly for the reasons mentioned herein.  They call the tool "Color Temperature" instead and in GIMP's newest version (2.10) this tool requests 2 data inputs.  They call one the "Original Temperature" and the other "Intended Temperature".  At the same time they have NO good explanation for where the "Original Temperature" is supposed to come from.

My thought is that given the fact that such a value must be used to process the raw data both the camera and DPP have a way to assign such a value.  I can't think of any good reason for keeping it a secret.  Given the vast amount of metadata, much of which is unknown to me, the idea that somewhere there is what I've been asking about seemed plausible.  I'm now beginning to think that the answer to my question may be "NO it can't be determined from the file" which means that the only way I can think of to know it is for me to keep track of it when processing my raw files.

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[Waddizzle]

”My inquiry was provoked in part because it appears to me that GIMP has changed in such a way that, I think, it may be doing what I've described.”

No, it is not.  As I said, you conclusions are based upon a totally false set of assumptions.  You will never fully understand what you are observing until you let go of some of these ideas.

A JPG files does NOT have a white balance setting or property.  Any white balance setting that was used to convert a RAW to a JPG gets “baked in” to the image, and the data is forever lost.

Image editors can analyze an image, and infer a color temperature, but whatever value the application might determine to be the color temperature of the image is based upon the false assumption that the JPG file is properly balanced and tinted.

There is no WB data in a JPG file.  Period.  

[aajax]

I completely get the point that the jpg format as well as other standard formats for storing images do not consider WB.  However, the metadata enclosed above, which is about WB did come from a JPG FILE.  The key point here, I think, which you are making is that it is not part of the image data.  By image data I mean the data which conforms to the standard which is processed when displaying the image.  In that, the image can be processed and displayed without using the metadata but the that does not preclude the metadata from being in the file nor from including information about WB.

[aajax]

I came across an interesting article by someone (Elle Stone) who knows a lot more about this than I'll ever know.  While the specifics pertain to a somewhat different situation than what triggered my question it appears as though I'm not the only one concerned about how to adjust White Balance on images that have already been developed (i.e., jpg files).  Check out the article at https://ninedegreesbelow.com/photography/white-balancing-camera-jpegs.html.