Blue snow

[Tom Rankin]

Better than yellow snow!

This picture:

has the classic 'blue snow' syndrome.

I can photoshop it to remove some blue, but is there a camera setting that will help avoid this in the first place?

This seems to happen in low light situations.

 

[the_swede]

This happens when you set your camera to auto white balance. Just increase the color temperature in the RAW editor or shift the color balance towards yellow a bit and red a bit.

 

[Tom Rankin]

This happens when you set your camera to auto white balance. Just increase the color temperature in the RAW editor or shift the color balance towards yellow a bit and red a bit.

Would a 'Fill-in' Flash help?

 

[DougPaul]

The blue snow is caused by blue sky...

Shaded portions of a scene will receive a higher portion of their lighting from the general (non-sun) part of the sky. If it is overcast, then it will be the whitish color of the clouds; if blue sky, then it will be blue. (Just like the surface of a lake.)

If you look into postholes with fairly low angle sunlight on the surface, the bottom of the hole will appear to be blue and/or the surface snow will appear to be yellowish. Same effect.


So the blue appearance of the snow is real. (When you look at it live, your eye/vision system compensates and reduces the percept.) What do you want to do with it in a photo? That is an artistic question--you could compensate the blue out, partially compensate it, or leave it. IMO, what one should do is highly dependent upon what else is in the picture since the compensation will affect everything. For instance, if the pic is mixed sun and shade, you might want the sunlit snow white and the shaded snow blue, the sunlit snow yellow and the shaded snow white, or split the difference. Since your pic is mostly sky-lit shade, I'd probably reduce the blue somewhat, but not entirely. And, of course, you can try various amounts of compensation to see what you like best.


BTW, color temperature is one dimension of adjustment but full color compensation is two dimensions of adjustment. (Color temperature assumes a blackbody spectrum which is not accurate for all sources. http://en.wikipedia.org/wiki/Blackbody)

Doug

 

[the_swede]

Hmm...you could try. It just might work. I usually just let the camera figure out the appropriate white balance. It's no big deal if you shoot in RAW. The white balance doesn't actually get applied to the image, it only writes that information into the file's metadata. But if you shoot in JPEG, the flash idea might just work.

 

[DougPaul]

Would a 'Fill-in' Flash help?

A fill flash would complicate the color problem--you would now have three different types of illumination*. However, in practice, it might be close enough to direct sunlight to reduce the blue snow percept (but this would be greater for close-in shaded snow than farther-away shaded snow).

Just to complicate the issue, the color of direct sunlight will change with time-of-day and atmospheric conditions...

One good way of dealing with this issue would be to try it both ways and selecting after-the-fact.

* In Hollywood, when they are shooting an indoor scene during daylight, they will put colored (plus neutral grey) gels on the windows to adjust the effective color temp of the outdoor views to match the indoor tungsten lights. http://www.kenrockwell.com/tech/whitebalance.htm

Doug

 

[DougPaul]

Hmm...you could try. It just might work. I usually just let the camera figure out the appropriate white balance. It's no big deal if you shoot in RAW. The white balance doesn't actually get applied to the image, it only writes that information into the file's metadata. But if you shoot in JPEG, the flash idea might just work.

You can also adjust the color balance of a JPEG after the fact. You just have a smaller range to work with and have to be careful that you don't bring out artifacts due to the JPEG coding.

Doug

 

[Grumpy]

Flash fill may help "normalize" the color in foreground features, but won't help correct the color in more distant features. You do stand the risk of introducing what amounts to a "mixed light" situation.

Most flash units, I believe, produce light that is about 6000° K -- roughly "daylight" -- color temperature. The blue cast from winter skylight on a clear day can push color temps well up into the 7000°s. Color of the flash unit's light can be modified by using gel filters in front of the flash tube, to balance with the ambient light. In this case you would use a blue tinted gel to achieve the balance.

G.

 

[MichaelJ]

White Balance is the answer here. When you're out in those conditions, surrounded by a lot of blue, some green, and virtually no red, your brain compensates and you still perceive the snow as white. But the camera, in its default automatic mode, isn't that smart, and when it processes its raw data into a fixed JPG image, it ends up looking bluish, and it stands out even more to you when you look at the photo on the computer back in the comforts of your home where your eyes are receiving all colors of the spectrum. It's not just snowy conditions, it's any time that you ask the camera to process color in a challenging scenario. Another case would be under a green leafy trail canopy with little or no sunlight coming through - you may find the ground bluish and the leaves with a pink or purple caste.

The advanced solution is to shoot in RAW and correct the white balance when postprocessing. The quicker solution is to look and see if your camera has a white balance setting (even the smallest point and shoots usually do). Try setting it to "sun", then to "shade", then to "cloudy". Each will put a little more color back into the photo. The simplest solution is to make sure more colors are represented in your photos for the camera's image processing engine to work with.

 

[Grumpy]

For grins, I just checked some photos shot yesterday with my new Canon PowerShot G11 (a Christmas gift to myself, and grist for another thread, maybe) under clear blue sky conditions with fresh snow on the ground. I shot in RAW format, which is my custom, using auto white balance.

As anticipated, the original images had a distinct (but not overpowering) overall blue cast. When opened in Photoshop RAW, the “as shot” color temperature showed up at 5300° K. Colors started to look more “normal” to me when I moved the color temperature slider to 6450° K, which probably better reflected the true temperature of the ambient light on the scene. I also added a little magenta (from +10 “as shot” to +13) using the tint slider, which warmed things a bit further.

This tells me that under similar conditions I should set the custom color temperature at about 6500° K, if possible. (Time to get out the manual – but I don’t think the PS G11 has that option. My guess is that if I used the regular “shade” setting it might come come close.)

The quirk to remember is that the cooler (more bluish) the ambient light the higher the color temperature. Likewise, more red-yellow in the ambient light means lower temp on the Kelvin scale.

My photo was shot out in the open. Tom’s picture has the added complication of foliage to further distort the color by adding a green component.

G.

 

[adkayaker]

simple solution

If you can shoot in RAW, most conversion programs have a simple white balance adjustment - you place a dropper icon on something white like snow, and the entire image is warmed up.

I use Breezebrowser and it worked good. If you shppt jpgs or want to wait to adjust in editing software, I tpyically adjust the curves blue channel, and color balance-going toward yellow from blue.

 

[Billy]

Tom

If you're shooting in auto-exposure mode, your camera sees all that white snow and says to itself "hey lots of bright tones here, gotta make sure I don't over-expose all that bright stuff"....so it under-exposes...ergo blue snow. I have had a different experience than some of those who've commented above: I've found that my auto-exposure pictures show bluer snow on overcast days. Obviously every situation is different with repect to camera, lighting, range of tones in the scene, etc. But try these two things with the camera...they might save you alot of time on front of the computer.

1) Blue sky day....meter on the sky, set your camera to that exposure, compose your shot, and shoot.
or
2) Regardless of the sky, intentionally set your camera to overexpose by 1-stop.

Not a panacea...lots of other variables involved...but like I said, it might save you some photoshop time.

Also, I wouldn't use flash. It'll make the closest ~15 feet of your pic look decent, but it might make everything beyond 15 feet look like dusk. Again, it depends on lighting, time of day, foliage coverage, etc.

If you're shooting digital, you're shooting for free, so try a bunch of different things.

 

[DougPaul]

If you're shooting in auto-exposure mode, your camera sees all that white snow and says to itself "hey lots of bright tones here, gotta make sure I don't over-expose all that bright stuff"....so it under-exposes...ergo blue snow. I have had a different experience than some of those who've commented above: I've found that my auto-exposure pictures show bluer snow on overcast days. Obviously every situation is different with repect to camera, lighting, range of tones in the scene, etc. But try these two things with the camera...they might save you alot of time on front of the computer.

Looks to me like you are confusing auto exposure with auto white balance.

1) Blue sky day....meter on the sky, set your camera to that exposure, compose your shot, and shoot.
or
2) Regardless of the sky, intentionally set your camera to overexpose by 1-stop.

Perhaps if you have an averaging meter. Many modern digital cameras implement a zone system which generally takes care of this problem.

Method 1 will tend to cause underexposure, method 2 will tend to cause overexposure.

The advice that I have seen is generally that underexposure is preferable to overexposure. Overexposure can result in blown-out highlights from which there is no recovery. Underexposure protects the highlights but may increase the noise a bit and reduce the detail in dark shadows.

With my cameras, I have occasionally had to underexpose by up to ~2/3 stop to prevent overexposure in bright spots, but never overexpose (for the best overall single exposure).

Checking the histogram will enable you to spot exposure problems in the field. Many cameras also have a mode which will blink saturated pixels.

Doug

 

[Billy]

Looks to me like you are confusing auto exposure with auto white balance...

Nope. I know the difference.

Method 1 will tend to cause underexposure, method 2 will tend to cause overexposure..

Try it some day. You'll see that both methods result in two similar exposures.


Tom, I'm trying to focus on your original question, which was fixing/reducing the blue/grey snow while shooting, rather than PS editing. I shot two quick series of photos today (link below). You'll see there are three photos in each series. All photos have aperture at f11. First photo is a basic point and shoot. Second photo is shot in Manual Mode after metering on the blue sky. Third photo is shot with exposure compensation set to +1. Same theme for the second series (photos 4,5,6). Note that the second and third photo in each series (method 1 and method 2 suggested in my previous post) produce similar results. Not perfect by any means, but a definite improvement over the first photo. Also note that none of these six photos comes close to clipping at either end of the histogram. As others have suggested, you can adjust WB in photoshop to improve it even further.

All photos taken with Canon Digital Rebel XT, tripod, aperture = f11,
Auto White Balance, no polarizer filter

Photo,f-stop,Shutter Speed,Mode,Exposure-Comp,Meter the scene or sky
1,11,125,Av,0,scene
2,11,50,M,0,sky
3,11,50,Av,+1,scene
4,11,100,Av,0,scene
5,11,60,M,0,sky
6,11,50,Av,+1,scene

http://walkinginthewoods.smugmug.co.../Snow-exposure/10964321_KDK6b#766164427_w24eS

 

[Grumpy]

A few observations about Billy’s test photos:

1) In the first series, my guess is that the auto white balance was influenced by the significant presence of the weeds bathed in low angle (late-day) light. Both the color of the weeds and the color of the light are naturally warm (lower K° temperature), which would tend to “tell” the auto WB to expose at a higher K° temp to compensate. Thus we still get bluish snow but the overall effect is very natural looking.

2) The second series, being all snow photographed under open sky under the same late-day light, is a completely different situation – essentially monochromatic. Here, the camera is seeing a very high K° (from the skylight) and so the auto WB compensates by shifting the WB for the exposure to a lower K° temp to compensate. This leaves us with the blue cast (and I see some blue-green in the third exposure of the series).

3) Given the subject matter, any of these exposures (to me) would have been “usable” – i.e., “tweakable” to “normal” with the ordinary Photoshop adjustments. It is my opinion that color renditions exhibited here do not result from the exposure changes as much as how the auto WB feature is “reading” and processing the color mix in the overall scene. Exposure changes will alter color saturation, but not color cast.

4) This might have been a more informative test series if photographed in RAW format, which would provide access to the “as shot” white balance K° color temperature.

G.

 

[Billy]

Grumpy, thank you for the helpful feedback. I guess my brain was stuck on the grey snow phenomenon, rather than the blue snow. Thanks again.