Blowout

My limited knowledge base tells me that a blowout is when the whites are maxed. That is indicated by the histogram going out of bounds on the right side.

What about the vertical color spikes. Are these considered blowouts also if they hit the top of the histogram?

I presume such a spike would cause a homogenous and bright color. Is that a fair assessment?

The cure for a non-white blowout but "blown out" color is what??? Lumenosity control?

the fisch

What about the vertical color spikes. Are these considered blowouts also if they hit the top of the histogram?

I presume such a spike would cause a homogenous and bright color. Is that a fair assessment?

No.
The histogram shows the distribution of pixels from RGB 0,0,0 to RGB 255,255,255. The "height" of a line is an indication of the number of pixels of that color in the image as compared to other colors. It has no absolute value and thus no meaning outside the comparison to other lines.

Cheers,

Vertical spikes in the middle of the histogram are a nonissue. What that tells you is that somewhere in the scene, you have a lot of one particular tone, or a lot of very, very similar tones. It may occur in all three channels or in just one channel. As long as it is not at the left or right sides of the histogram, you are fine.

Actually, I need to be a little bit careful. The spike can be at the immediate left or right of the histograms, as long as it is not at the far left or right end. If, for example, the peak occurs at the far right, along the edge of the histogram box, then you have blown highlights (overexposure for those aprts of the scene). If it occurs even just a millimeter in from the far left end, this means you have a large white area, but with details if present and you have not overexposed the any part of the scene.

Once you have blown out part of the image, there really isn't much you can do. You can bring the tones down, but any detail which was in the original scene simply wasn't captured in the first place. You'll still have a textureless blob, but at least it won't be as bright of a blob.

I've found that reds tend to blow out the fastest, both in film and digital. If I am shooting something with a lot of bright reds in it, I'll check the RGB histogram. If I am getting clipping in the red channel, I'll underexpose the image a bit, and deal with it in in Photoshop. I hate that workflow method, but if it is what is necessary to get the shot, I'll do it.

Larry - Are you referring to individual RGB histogram where just one color is up against the right side? In that case, that single color channel is in fact "blown", and can lead to a loss of detail. A regular luminance histogram could show no highlight clipping, even if one of the three RGB channels is blown. It's not common, but possible. In that case you could treat the individual channels just like a normal luminance view, and reduce exposure to prevent it.

Like Mark said, I wouldn't worry about anything in the middle of the histogram.

One way those spikes are useful Larry, is for inferences about color balance. Seeing lots of blue where none should be? Take a gander at your WB settings. Same for yellows. It's lots more empirical than I would like after years of using a color meter, but with a little experience and thought you can use those spikes as I describe. Otherwise, watch that right side.

Regarding "what to when the highlights are blown?" - what you should not do (well, in my humble opinion) is just pull down the curves or levels. What happens then is that you darken everything, even the colors right next to the blown out area, which will therefore start to stand out against dark colors surrounding it and look exceedingly ugly. What I usually do when I have a blown highlight and want to darken the shot is that I apply an S-curve to achieve a smooth rolloff (transition) into the blown area while darkening the midtones and the shadows.

Basil

Thanks for the replies so far.

I use auto WB most of the time. Seems to be the only way to go. I can change WB in processing if it needs to be tweaked.

My D300 has choices for the histogram.

I use the combo with RGB showing individually and the main histogram in white.

I understand the right side indicates blow out. I understand any color exceeding the right side is blown.

I did not understand the meaning, if any, of the height of a any color. I did not know if that meant it was blown. Apparently it is not unless the color goes into never-never land on the right of the histogram.

So, I won't worry about the height of the histogram, right? Or the height of individual RGB as long as it does not go off the right side.

the fisch

"Those who are unaware, are unware, that they are unaware." Derived from Socrates

Mark Stahlke and Dan Borzynski summed it up pretty well.

Sounds like you've got it Larry. My concerns for WB reflect the rather unique nature of much of my shooting, compared to basic nature shooting. A large portion of my professional work requires a direct hand off of image discs to the client without opportunity for post processing. Especially around artificial light sources, in early morning or late evening "warm" light, or when using strobes, auto WB can lead you afoul. Just be aware of it, and shoot the same scene on some of the other WB settings as a "bracket" and you're likely to find one that pleases more, maybe even cutting your post-processing requirements.

The closer to "right" my images are once a client opens the discs, the more likely I am to acquire a regular client. Since more than half of our business is from long-standing clients, I can't risk auto WB. Heck, I even use in-camera focusing if the client wants it!

Hank,

I'm planning a trip to the "Greatland" in August, provided the economy doesn't continue to nosedive. Will be on the Matthews River on the south slope of the Brooks.

Looking forward to some photos of crystal clear water, mountains, sheep, etc.

Several years ago I was on the S.Fk. Koyukuk and the smoke was horrendous. Tundra was smoldering from many fires all across AK.

Anyway, I don't alway use auto WB; and I also use manual more and more. On tripond I'm in manaul focus. With that expertiese I might even survive AK yet one more time, eh?

Kindest regards,

the fisch

A false notion which is clear and precise will always have more power in the world than a true principle which is obscure or involved.-- Alexis de Tocqueville, Democracy in America

That will be a grand trip Larry. It's great country up there, though much nicer without the smoke Sounds like you were there while a friend of mine was in the general vicinity trying to do field work with 60 days of contracted helicopter time. They manage only 11 days of flying!

Better luck this time around!

I did not understand the meaning, if any, of the height of a any color.

The height of a histogram peak corresponds to the number of pixels that have this luminance (for the "white histogram") or R, G, and B (for the separated histograms) value.

BG