Histogram

[2069]

Hi,

 

I have read everywhere that in digital capture, one should push the histogram to

the extreme right so that the whites go complete white.

 

My question is, what if the image doesn't have whites?

 

I have a 400D and i routinely get indoor shots where the right side of the

histogram is blank as much as 1-2 stops. I would think that the image is

underexposed, but then i think that may be because the scene doesn't have any

white to begin with, hence the dark result.

 

If i move the levels slider on such an image and fill the right side blank of

the histogram, the image becomes brighter. Now i can't decide if this one was

right or the earlier one....is it necessary to keep your histogram tight, end to

end, irrespective of weather the image itself has any whites or not??

 

Can someone help me out?

 

regards,

anurag

[rich_morgan1]

If the image doesn't have whites, do not expose to the right. In those situations, I typically

expose in the middle, and bracket a half stop and a full stop to the right of middle.

[vrankin]

I suppose it's a matter of taste. I avoid blank whites on the right extreme. Coming from many years of film, I would rather have details appear in the whites and let the shadows fall more extreme left. Surprisingly, there's still detail in them when printed.

[rainer_t]

It depends on the desired end result as well as on your workflow.

 

If your endresult shall be as original as possible, its histogram will also not touch the right side. So, if you shoot in-camera-jpg, you shouldn't expose to the right in such a case, in order to have good results straight out of the camera. But if you shoot raw, your results will be better (regarding noise), if you expose for the right, and correct in postprocessing.

[emre]

To repeat for clarity, even if there are no whites, it is better to expose to the right when shooting RAW, then pulling the exposure down. This will leave you with cleaner shadows because they will be captured higher up in the histogram, where there are more steps.

[2069]

Thanks a lot.

 

So basically one shud expose to the right, even if no whites in the scene. But where to actually place different tones is a matter of taste/personal choice.

 

Is that right?

[brian_ellis19]

I agree with Emre. The reason why you expose with the histogram as far to the right as possible but without blowing out the whites doesn't have anything to do with the color "white" as such. It's just a way of keeping as much of the image as possible in the area where you have the most steps without losing detail in the brightest area in which you want detail. And you still want to do that even if there are no "whites" in the scene, it's just that instead of exposing as far to the right as possible without losing detail in the "whites" (since there are none) you expose as far to the right as possible without losing detail in whatever the brightest value in the scene happens to be. But either way, whites or no whites, the idea is to get the exposure into the area where you have the most steps. At least that's always been my understanding, I'm open to correction if I'm wrong.

[phule]

You should be using the term "highlights" instead of "whites."

[phule]

Sorry, I should have also included this link:

 

http://www.luminous-landscape.com/tutorials/understanding-series/understanding-histograms.shtml

[phule]

Argh! This was the link I wanted to include. I really need more coffee this morning.

 

http://www.luminous-landscape.com/tutorials/expose-right.shtml

[ellis_vener_photography]

"I have read everywhere that in digital capture, one should push the histogram to the extreme right so that the whites go complete white.

 

My question is, what if the image doesn't have whites? "

 

You have either read wrong information or mis-understood what you have read.

 

What you have likely read is the advice to "expose to the right", but you should not push this so so far that anything that isn't a specular white -- a white with no detail -- is "clipped" to a detailless white.

 

This advice is given so that the camera produces a cleaner, more noise free image. It is akin to the old film days of idea of exposing a negative for the shadows to capture as much information and detail as possible) and then printing for the highlights to reproduce that detail.

[william-porter]

Read the article that Rob Bernhard referenced. There's a LOT of misunderstanding about the "expose to the right" idea. The article will make all clear.

 

The basic idea is this: The way that digital cameras work, the lion's share of the info that is captured in an image is up in the brighter end of the photo. Imagine that your sensor consists of four buckets. The bucket used to capture info about darks is a one-gallon bucket. The second bucket, for mid-tone shadows is a two-gallon bucket. The third bucket (for mid-tone lights) is a four-gallon bucket. And the bucket for the upper highlights is an eight-gallon bucket. If you imagine the data as water, to capture as much water as possible for later processing, you'd want to get as much of it as possible into the bigger buckets. These represent the right side of the histogram. But the mistake some people make is that they think shooting to the right means deliberately blowing out highlights. NO, absolutely not. Because there's less data in the dark end of the histogram, blowing out your blacks usually means you're losing less useful info. Blowing out your highlights on the other hand means that you're losing MORE useful info. So exposing to the right means: try to push the histogram to the right of center -- but avoid blowing the highlights. Once they're blown, they're irrecoverable.

 

FOOTNOTE: It's not immoral or illegal to blow the highlights. You just need to know what you're doing. In some photos, losing a little detail in a cloud or the white of someone's socks or something is a relatively small price to pay for a better exposure of the important parts of the image. That's why, when I'm reviewing my exposure, I like to see BOTH the histogram and the blinking feature that shows blown darks and lights.

 

This works better when you're shooting raw, by the way.

 

If you do this routinely, your photos will look a tad washed out when you view them on the computer the first time. But it's easier and more effective to pull the curves down (darken the image) in post-processing than it is to pull the curves up (lighten the image).

[colinsouthern]

Just to throw some science into the mix ...

 

With the 12 bit A/D conversion that's typical of most SLRs, each of the 3 colours can be resolved into 4096 different levels - BUT - they're not allocated in a linear fashion.

 

The camera will allocate 2048 bits of information between the right hand side of the histogram, and 1 stop down. 1024 bits to describe the area between 1 & 2 stops down ... and 512 for the next stop etc.

 

Unfortunately - this means that the camera is recording, with the most detail, the bit that our eyes are the LEAST sensitive to - and only a few levels to describe the bits our eyes are the most sensitive to.

 

So ... when you capture a scene - and the histogram stops 2 stops short of the right hand end you've effectively wasted 3072 of the 4096 available levels!

 

As others have said, if you max out the histogram you'll capture (in this example) 4 times as much info - which you can then "put in it's correct place" during post-processing (assuming that you're shooting RAW).

[2069]

Thanks a lot everybody. Brian i actually meant highlights. I've read Luminous Landscape article and its' very nice. I try and follow that as much as possible, even if its a bit difficult to do that.

I started having all these doubts when i read about underexposure problems with my camera. As it turned out, my copy also gave dark indoor pictures. I thought may be the pictures are dark because the scene itself has dark/gray tones.

Thanks everybody.

[2069]

Actually my question was...suppose i shot a picture that's made of middle tones with no highlights as such. And the histogram shows 1 or 2 stops blank at the right side, because may be the camera underexposed or may be its the right histogram for the given image, i don't know.

 

Now, is it okay to ALWAYS pull the levels slider to fill the blanks and make the image brighter? Should one always make the histogram fall end to end, or leaving the blanks at the right is fine for a middle tone picture?

 

regards,

anurag

[rich_morgan1]

If you shot raw, haven't burned out any highlights beyond recovery, have a raw converter with

a wide range exposure tool (+/-2 stops minimum) you can expose far right. Note though

that your image in that situation will not be an accurate portrayal of the light. You'll need to

reduce the exposure level in post processing for accuracy, otherwise your image will be

overexposed.

 

Note that in artistic terms, there is no technically correct exposure. The exposure is correct

when your sensibilities are satisfied. That might be completely different from what others

might prefer.

[colinsouthern]

Anurag,

 

Camera metering in modern Digital SLRs is (unfortunately, in my opinion) the same as their traditional counterparts - in that it expects an image to be 18% grey.

 

If you shoot a white card, it'll under-expose it by 2 stops and you'll get a grey card. If you shoot a black card, it'll over-expose it by 2 stops - and again, you'll get a grey card. In both cases the histogram will be about 2 stops under.

 

If you shoot something with more contrast the camera will start to "spread out" the histogram, starting from about 2 stops down (assuming correct exposure) - right up to the point where you have total contrast (say, a photo of the moon with black sky around it - you'll typically end up with 2 spikes - one at each end of the histogram).

 

If you're shooting RAW and want to ensure that you're capturing the most amount of information with the least amount of noise then you need to ALWAYS max out the histogram - no exceptions. Hovever - if you do max out the histogram - and you're capturing a dim, low contrast scene, then that photo will look VERY over-exposed on your camera's screen, and you'll need to make a large adjustment during post-processing ... however, if you do this you'll end up with a cleaner image than if you'd captured it 2 or 3 stops short of the right-hand-side of the histogram.

 

Frankly, it would be nice to have a metering mode on the camera that altomatically maxed out the histogram regardless of the scene, but unfortunately there isn't - due (I guess) to the desire to carry on from the metering of film days.