gdanmitchell
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Mike_5D wrote:
There's blown out, and there's BLOW OUT. Sure, if it's really gone, ie 255/255/255, then you won't get any color info back. But a raw file has more DR than the JPG preview on which the histogram and blinkies are based. So if you're just starting to get blinkies, which usually happens first in the whitest part of the scene, then yes, you will be able to recover. I just shot into the brighest part of an overcast sky. The camera, with the picture style set to faithful) says nearly the entire sky is completely blown out. Lightroom says the brightest part is 97-98%. I have to push the whites slider to +30 before Lightroom's overexposure slider matches the camera's. ...Show more →
[Fixed a bunch of typos in this post.]
It is true that the blinkies (or the right edge of the histogram, to be honest) do not always indicate that all three channels have recorded their maximum luminosity values in the captured raw file. These indicators are generalizations to some extent, and there's some nuance to the whole issue. (For example, I earlier mentioned that blowing tiny specular highlights may not be an issue in some cases and that it is possible to think of cases where a creative decision to allow highlights to blow out can be fine.)
And, indeed, you can sometimes recover (or amplify) some remaining detail from areas in some raw files that appear to be blown out. Note that the words "appear to be" are doing a lot of work here. If the luminosity data of the three channels have actually hit their max for pixels that should ideally be recorded as below-maximum levels, the detail is gone and you cannot get it back. But raw files seem to have a bit of "space" between what the camera indicates to be blown out and that unrecoverable state. You'll have to learn about this through experience with your own camera.
But the "protect the highlights" rule still applies!
Since we're getting into nuance now, I'd disagree with the earlier suggestion that all three color channels must hit the maximum luminosity level before we have a "blowing out" problem. That is, indeed, a bad thing and it results in the camera essentially recording pure white where there should be something else. But it can actually happen when we hit the maximum and can't accurately record the value for a single channel.
Accurate color (with the exception of pure red, blue, or green) comes from recording an accurate balance among the three channels. (It is a bit more complicated than that, but I digress...) Imagine that some very slightly pinkish almost-white color comes from R:255, G: 250, B: 250. The ratio between those three values is what produces that subtly pink almost-white color.
Now let's overexpose that a bit so that an accurate version of that color would require (and, again, I'm simplifying) R:260, G: 255, B: 255. See the problem yet? In this case we'll blow out the R channel since it now requires a value higher than 255. Now all three channels would be 255... and the pink tone is gone and we just get pure white. The color shifted.
There are plenty of obvious real-world examples of this in photography that we see all the time on the internet and, unfortunately, even in prints from people who should know better.
Let's consider the ubiquitous sunset or sunrise photographs, in which the red channel can be extremely hot. In this case your camera may not even show that the image is blown out — no blinkies, and no "past the right edge" tip of the luminosity curve. You might be tempted to push to almost the right, just below where the camera indicates that you are going too far.
But don't.
The camera is (unless you use an accurate three-color histogram and look very carefully) basing its indication on a sort of average of the three color channels... and if you push all the way to the right you can easily blow out just the red channel even thought the blue and green channels are well below that level.
Here's the problem. In your photograph there are things like sunset-lit clouds that are both very bright and very hot in the red channel. You'll lose important details in those clouds if you let the red channel blow out. I regularly see photographs with brilliant and overly-intense clouds... that have lost their details. (It could happen in the other two channels, too, but we see it crop up most commonly with overly hot red channel images.)
In addition, let's not forget that color balance issue that I described above. Not only do we lose detail in that single hot channel, but color balance among the RGB channels is now thrown off and the color of that brilliant sunset doesn't look right either. (Another place where this problem shows up a lot is with fall color photographs, where letting the red channel get too hot results in leaves that lose detail and may have odd color shifts.)
Again: protect the highlights, whether considering the composite white or the individual RGB channels.
Dealing with these issues can require attention at the time of exposure, and sometimes that means considering how the image will work best in the post-processing phase and then adjusting exposure with that in mind. If that's too much work, well that is a preference that anyone is entitled to have. But some folks feel that the better results are worth the extra work.
Oh, one more "trick" for those who do find themselves with something blown out in these ways. It is sometimes possible to transfer some texture to the blown to area of the image from another part of it. On occasion I've had very bright rocks or small sections of a sunlit cliff blow out in an image that otherwise looked fine... and that pure white area sticks out like a sore thumb. One solution can be to clone a bit of texture from a non-blown area and apply it to the blown out spot, perhaps adjusting the opacity of the clone so that it is very subtle. There are other tricks that can apply, too.
YMMV.
Edited on May 29, 2023 at 05:50 PM · View previous versions
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so here's Jim