This is something for the technically minded.

It is well known among Photoshop users that its raw image converter has difficulty in reproducing the authentic colours of daybreak and sunset scenery. Virtually any colour hues that come within the yellow and orange spectrums are rendered in a muddy mix rather than their brilliant purity.  Canon’s DDP does not do a better job than Photoshop so I suspect they share similar algorithm for the conversion process.  Being ignorant of the technicality involved, I can only attribute the abnormality to bad colour decoding by the converters.  As a remedy, for years I have resorted to Capture One for converting images that contain dominant yellow and orange hues in their composition such as those taken in times of the golden fall.

Recently, I came across a forum discussion on the incorrect Caucasian skin tone reproduced by the Canon 5DII and someone introduced to a site which explains the effect of twisted colour hue of the camera profiles embedded in the Photoshop raw converter.  According to this site, the colour shift was caused by the twisted differentiation of hue intensity incurred by the Adobe camera profiles as against the true colour recorded by the camera. Obviously, raw images converted in Lightroom also inherits similar irregularity since they both share the same conversion engine:

http://dcptool.sourceforge.net/Hue%20Twists.html

I can understand generally the concept behind but not its detailed technicality.  Anyway, the site provides a tool for download – dcpTool which can produce an untwisted camera profile file from the Adobe standard profile for use in the raw converter.  When applying this untwisted profile, one can regain the original hue intensity and colour purity as recorded by the camera.  I have tried it out and yes, it works beautifully.  You have to run a Dos window in order to execute the dcpTool for creation of the new profile.  The untwisted profile cannot be run in the DPP environment in its present form.  May be someone can work it out.

So, by default Canon may be able to produce pleasing skin tone but it may not be the correct tone.

Interesting and informative, although I must admit that I can only understand little of it. Some questions for you that may help me to understand more.
1. Is that hue twist applied to all dpp profiles? Is there one untwisted profile (e.g. standard/neutral?)
2. Can we edit a profile to obtain an untwisted hue?

AY2007 hing,

Answers to your 2 questions:

1) No. According to the site, we need only to create an untwisted dcp profile from the Adobe Standard Profile, for PC, located in C:\ Documents and Settings\All Users\Application Data\Adobe\Camera Raw\Camera Profiles\....  Please note that PS stores camera profiles of all supported cameras here and each brand\model of camera has an Adobe Standard.dcp file.  Use the specific camer's Adobe Standard.dcp for creation of the untwisted profile file.

2) Theoretically yes, we can create an untwisted file from each of the different camera profiles provided by the camera maker.  However, whether that "untwisted" file is indeed an untwisted algorithm I really don't know.  

So far, I have created untwisted profile files for the 5DII, 1Ds and 1DsII from each of their Adobe Standard profiles.  It seems only the 5DII one works great, the other two have trade offs.  For colour fidelity, Capture One is still king.

You can download the 5DII untwisted file from here:

http://download.hansheino.nl/pics/5D2_ACR_Standard_Untwisted.zip

and put it in the folder as mentioned at 1) above, then open PS ACR, and at the Camera Calibration tag under Camera Profile pull down menu, you can find this untwisted profile.  You can see the effect only in images with orange and yellow hues.

Thanks C Hing, I don't use PS so the untwisted profile cannot help me, at least at the moment. But I would really like to know what is the difference between using this profile or not. Do you have any picture sample showing the effect of different profiles (ACR, ACR-untwisted and DPP)?

I have made sample images as per your request.  For comparison purpose, I have used 4 profiles for conversion of each of the sample 5DII raw file, namely:

1) Adobe Standard Profile which is PS's standard ACR profile,
2) Canon Standard Profile, same as found in DPP standard picture style,
3) Canon Neutral Profile, same as found in DPP neutral picture style and,
4) dcpTool untwisted profile, created based on Adobe Standard Profile using the dcpTool, which is supposed to retain the original hue intensity as recorded by the camera.

Sample Image A - Shek O Beach: you'll notice that the untwisted profile sample has the best colour of the sand beach and has better contrast for the blue sky and the waves. Both the Adobe Standard and Canon Standard Profile has a magenta tint.  The Canon neutral profile comes close to the Untwisted profile but the image has a dull over tune.










Sample Image B - Shek O Tin Hau Temple: One first glance, the difference is not so obvious.  However, when examined carefully, you'll notice the difference of the red in the untwisted profile image is more realistic to the Chinese characteristic red, which has a distinctive orange tint.  The Chinese characters 海不揚波，天后聖母 etc. are much more authentic in colour.  










Sample Image C - Shek O Village: those who have seen these colourful houses in Shek O Village will recognise their realistic colour.  It can be immediately identified that the orange house is too reddish in the two images converted in Adobe and Canon Standard profiles.  Although the image from the Canon neutral profile comes slightly better but it is the one from the Untwisted profile that scores the most realistic orange tone.  This is also evident from the bits and pieces on the right hand side of the picture, the yellow colour of the "Garden Bakery" rack comes out best, the tomatos are faithfully coloured in orange red whereas the different forescent colour price tags on the vegetable rack are realistically rendered.

the last set of photo can show the difference obviously.
but from the beginning of the story, i dont understand wht is "untwisted profile" mean.

The meaning for untwisted profile is best explained in the original site that raised this subject:

http://dcptool.sourceforge.net/Hue%20Twists.html

And I quote in its first paragraph:

"DNG Color Profiles allow for a complex set of what are in effect look-up tables that can translate from a color as photographed to another color as displayed. What's more, these look-up tables provide for the ability to make these color shifts dependent on the intensity. So two pixels with the same tint (a hue and saturation combination) but different intensities (values), can translate to pixels with different tints. This is what Adobe's new generation profiles do."

Untwisted profile is a profile that completely removes these colour shifts. In fact it is a subject raised mainly in relation to skin tone.  I don't have portrait photos taken with 5DII so my sample pictures are not good demonstration of the untwisted profile.  Nevertheless, they do illustrate the effect of colour shift in the red - orange - yellow hues.

Thanks a lot, C Hing. Those pictures really show how big the difference can be.

There is always a debate on whether a picture should be looked like real or beautiful. As mentioned somewhere in the links you provided, the twisted profiles can indeed make a picture appears to be more beautiful (the exact words may be different, but with similar meaning). That is supposed the reason why they are twisted.

So my major concern with the untwisted profile is not how true its color is. I am more interested in whether the untwisted profile can remove some digital picture color conversion defects caused by the twisted profile (e.g. uneven color transition in sunset pictures). Do you have any picture that is easier for us to see this effect?

Ha, ha, ha, you are making me to work again - just kidding.  I'll search my 5DII archive again to see if I can have something more prominent to show the difference.   

As I said before, this is stemmed from the discussion on the accuracy of skin tone, which is an issue more important than making the picture to look aesthetically beautiful. You may like to take a look at this discussion link which speaks much better than my explanation:

http://forums.dpreview.com/forum ... mp;message=32483001

Further to my post above, I wish to clarify that the untwisted profile isn't a magic cure but, as I perceive it, should be regarded as just an additional profile for use with the Adobe ACR profiles as well as Canon's picture styles for whatever application as may deem fit to one's preference.  I am in agreement that there must be a reason for the twisted Adobe profile - since its purpose is to make the colour look aesthetically beautiful - similar to the highly saturated colour hues of high definition TV.

For me as mainly a landscape photograher, this untwisted profile vs twisted profile is less of an issue.  It is handy if we want a reference of non twisted colour hue but that doesn't mean we need to use it extensively nor exclusively.  However, those portraiture photographers may find it relevant insofar as accuracy of skin tone is concerned.

I have read the depreview post. Seems that the people there does not have an agreement yet whether the untwisted profile can indeed produce more accurate color. Some people state that the dpp neutral picture style is more realistic. Anyway, as I said, I am not really concerned whether the color is more accurate or not.

When I read this thread at the very beginning, the point that caught my attention was "the hue of a color in the picture may change when the luminous level change". The scene where a gradual change of luminous level can be seen, e.g. the sky during sunset may have problem here.  I am not sure how serious that effect may be but I think that is a reasonable question, and would really like to see more samples which can display that hue twist effect.

There have been only little posts here about technical issues like that. Thanks for bringing it up.