Sky color & Photoshop

[dmammana]

How does one get a proper sky color using Photoshop?  

I see wonderful photos from time to time with blue sky and clouds that look as if they're viewed out a window instead of on a computer monitor.  Even with what I think is proper white balance, curves, etc. I just can't seem to get the blues to take on that bright blue sparkling look of the real thing like many other photos.  

Any tips or suggestions?  Are there rough proportions of R-G-B to use as starting points for bright blue skies?  

Thank you in advance!   --Dennis

[fennario]

If you are using ACR 4.1 then one trick is to go to the HSL tab and decrease the luminosity of the blues in the image.  This will darken and deepen the blues in skies, aproximating what you can do with a polarizing filter.  I often do the same with the greens as well in landscapes.

[dmammana]

My concern is not about darkening the sky, it's about color.  

The sky has a rather specific color that I'm unable to duplicate;  either it turns out slightly reddish, with too much cyan, etc.   All the playing in the world doesn't seem to get me to the right color... there's got to be a trick!

[Jonathan Wienke]

It's called color management.

First thing is to calibrate and profile your monitor with a hardware device so that you're acutally seeing meaningful colors on you screen. If you don't do that, than any color edits you try in Photoshop are the equivalent of measuring with a rubber ruler; pointless and frustrating at best.

The next step is to color calibrate your camera; Tom Fors has an excellent Photoshop script floating around that color calibrates ACR to your specific camera. Google ACR calibration script and you'll find it easily. You'll need a Color Checker for this; if you don't have one, buy one.

Once you've gotten this far, you can at leat trust the color you see on-screen, and accurate color is generally as easy as shooting a test shot with the Color Checker in it somewhere, and doing a click white balance on the second-lightest gray patch. Then apply that white balance to the rest of the shots made in that lighting and you're good.

[dmammana]

I do calibrate and profile all--BTW, it should be called "anger management" instead of color management  , but I will check out the ACR calibration script.  

Thanks!

[Dale_Cotton]

The sky has a rather specific color that I'm unable to duplicate; either it turns out slightly reddish, with too much cyan, etc. All the playing in the world doesn't seem to get me to the right color... there's got to be a trick!

I've had this happen many times working with film scans; finally developed a theory about what was going on: if the sky starts out cyan, and I shift it toward blue, any pixels in the sky that were already blue will shift into magenta. I also see cyan skies all the time in P&S JPEGs; I assume because they get the white balance wrong.

Never found a solution, but thought you might gather some small solace from knowing you're not alone... ;)

[Jonathan Wienke]

I do calibrate and profile all--BTW, it should be called "anger management" instead of color management  , but I will check out the ACR calibration script.

Yeah, color management can definitely be a PITA to get set up and working, but once it is all configured properly, it is sooooo nice...

[dmammana]

Well, there has to be a solution and--one way or another--I'll find it.  It may wind up being a Rube Goldberg affair, but the answer's out there!

[dmammana]

Just out of curiosity, why click white balance on the second-lightest gray patch rather than the whitest one?

[Blendenteufel]

Before you spend too much time calibrating your camera and still not getting were you wanna get (calibration is only really working for stable and repeatable lighting conditions), try to use the LAB color space for adjusting colors. A good starting point is the book "The canyon conundrum".

Basically, the "a" (magentA-green) and "b" (yellow-Blue) allow for much finer adjustments and together with masking techniques (e.g. luminosity mask) will get you  a big step ahead. Most of the time though you'll have to compromise and give up either hue, saturation or luminosity (the book explains more detailed why).
 
Most importantly though, not all skies are the same, depending on your altitude (UV-level), the humidity, pollution, time etc. So at the end you'll have decide which color you want the sky to be...

[PeterLange]

How does one get a proper sky color using Photoshop? 

After Color Management etc. is accomplished, starting point should be accurate Hue and accurate Saturation, both together representing the spectral intensity ratios of the original color. Whereas Brightness is of course a relative thing, for reasons of dynamic range compression (scene to output / monitor) and due to the "pleasing" tone curve applied during Raw processing.

For a preferred reproduction of a blue sky, I typically don’t feel the need to shift the Hue away from accuracy. However, I like to have the blue sky:
more saturated (rather than accurate)
and darker (relative to other colors)
in a HSB sense.

One option is the Hue/Sat.-tool in Photoshop and a diametrical setting of negative Lightness and positive Saturation, applied to a respective blue color range. Problem is that both sliders are effecting both, HSB saturation and brightness in a contradictive way (see HSB readings). For example, a negative Lightness setting reduces both, HSB brightness and saturation. Hence, quite strong diametrical settings of e.g Saturation +30 and Lightness –30 are needed to achieve little effect as desired. This in my opinion is not a preferred approach.

It’s similar but somewhat less problematic with the Replace Color command. The Saturation slider again mixes HSB saturation and brightness. But the Lightness slider now seems to be focused on HSB brightness only. So for example, when you click-select a pale blue sky, it should get "deeper" with Saturation +15 and Lightness –10.

Another option is the Selective Color tool and a positive setting of the Black slider with the Blue and Cyan color range, respectively. This reduces HSB brightness while also adding a bit HSB saturation. Together with a layer mask (to protect blue hues which are already darker) I find this to work quite well. IIRC a basic setting of Cyan Black +15 and Blue Black +25 (at finally reduced Opacity) was part of a Provia look action from atncentral.

That said, I'm not sure if this would be the solution you're looking for, since you're obviously having an issue with the color alias hue angle. At the end of the day, preferred rendition of memory colors might be a matter of individual taste...

Peter

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[NikosR]

The next step is to color calibrate your camera; Tom Fors has an excellent Photoshop script floating around that color calibrates ACR to your specific camera. Google ACR calibration script and you'll find it easily. You'll need a Color Checker for this; if you don't have one, buy one.

[{POST_SNAPBACK}][/a]

I suppose you're not suggesting color managing the camera for all the different light conditions one may encounter? This is not practical for the general photographer (e.g. not the one who only shoots under controlled and consistent lighting conditions). Should I color manage my camera for shooting in my garden full of green foliage in a clear morning in June and re-manage for shooting next to my light ochra painted wall at midday when it's cloudy in December?

Even if I could do that, would I want to? Would I want the green cast thrown on the subject's face to be reproduced exactly? And exactly like what? Like my human eye saw it or as reported by a colorimeter?

Camera colour management is a whole different beast than  colour managing your monitor or your printer, exactly because of the often uncontrollable lighting conditions and because of what you're judging against is the subjective interpretation of colour by the human brain.

BTW, you can calibrate ACR but you cannot color manage your input (i.e. use camera ICC profiles) which is what an end-to-end colour management would require as used in scientific photography. At least last time I looked you couldn't.

Matrix calibrating for the primary colors (not profiling and colour managing, there is a very real difference between these) the raw converter for your camera for average normal conditions has in my experience proven to offer only very limited (if any) benefit. In my experience  I have found it is not worth the trouble especially when one considers how many factors can influence the quality of the calibration.

Additionaly, by calibrating to a nominal lighting condition one assumes  linear sensor  response to different wavelengths and 100% non-visible light filtering which I believe is far from true in many cases.

Modern cameras seem fairly consistently matched ex-factory anyhow so standard raw converter 'profiles' SHOULD work pretty decently. I find ACR and Lightroom one of the worst for Nikon cameras in this respect and maybe for people who use these raw converters, calibrating them might be a good proposition (with all the caveats about proper calibration and non-linear sensor response mentioned).

The main usefuleness I can see for the average photographer would be when 2 or more cameras would need to be closely matched for workflow efficiency.

I am bypassing these problems with Nikon by using Capture NX which seems to be able to represent my cameras very nicely. Of course anyone can experiment with calibrating their raw converter and see if it is worth the trouble in saving them color correcting keystrokes.

There's a good expert discussion about calibrating ACR here:
 [a href=\"http://luminous-landscape.com/forum/index.php?showtopic=17064&st=0]http://luminous-landscape.com/forum/index....opic=17064&st=0[/url]
which poses more questions than gives answers.

[dmammana]

This is the ACR camera calibration script Jonathan recommended:  http://www.fors.net/chromoholics/   I understand you calibrate your camera once (usually for daylight) and that's it.  (I guess tungsten requires a separate calibration)

Check out the FAQ, getting started guide, etc. for more information.

--Dennis

[Jonathan Wienke]

Yes, that's the one. A calibration based on a daylight shot (Color Checker lit by direct sun on a clear day around noon) is pretty versatile; I've found it useful in wide variety of conditions. The main exceptions seem to be spiky light sources with strong color casts like sodium vapor lights, but it's easy to run another calibration preset for the few lighting conditions that cause problems. In most cases, all one needs to do is set white balance properly, and all the rest of the colors fall nicely into place without further tweaking necessary.

[dmammana]

Is there a reason that one should click white balance on the second-lightest gray patch rather than the whitest one?

[Jonathan Wienke]

There are 2 actually:

1: The second-lightest patch (for some very obscure reason) is the most neutral patch in the Color Checker. The other patches all have small color casts. I don't know why.

2: Click white balance doesn't work properly when the color channels are clipped or very close to clipping. Using the lightest patch as a guide to ensure you have no color channels clipped means you are guaranteed an accurate white balance when using the second-lightest patch.

[dmammana]

Maybe I'm slow today, but I'm not following the second sentence of your reason #2.  Can you elaborate a bit?  Also when you say "click white balance"... specifically where in PhotoShop are you referring to?  I often use the eyedroppers in curves for this.

Dennis

[Jonathan Wienke]

Click white balance is in ACR, setting RAW conversion parameters. You want to get colors and tonality as close as possible to your final print in ACR for a variety of reasons. The most obvious is batch processing; you can apply conversion parameters from one image to as many others as you like. The other main one is that with calibration parameters set properly in ACR (which is the point of the Fors script) you don't need to futz with colors in Photoshop any more, all you need to do is sharpening. You shouldn't be using curves to color correct in PS to get true-to-life colors, that should be taken care of while the image is still in ACR. And using the curve adjustment in ACR is the best way to get the tonality you want without compromising color accuracy.

Digital sensors typically exhibit a small degree of non-linearity just before clipping. So if you use a white reference for white balance, you have two sources of WB inaccuracy: the possibility of a clipped color channel, and the possibility of one of the color channels being in the small non-linear zone just below the clip point. Either of these can skew the accuracy of your white balance reading if you click white balance.

If you use the second-lightest gray patch in a RAW where the lightest Color Checker patch is about level 250 when the Exposure setting is at 0, you get the most accurate click white balance because you're using the most neutral patch in the color checker, and you're safely below the exposure range where clipping or nonlinearity can skew the accuracy of the click WB reading, but high enough on the exposure scale where you can still get a highly accurate reading. It's sort of the sweet spot in the tonal range where click-WB accuracy is greatest.

[Gordon Buck]

Pixel Genius has their Color Kit with a "blue sky" special effect that seems to work well.

[dmammana]

Excellent explanation.  Thank you!