Histogram accuracy when shooting RAW

[Drake]

I was wondering, how accurate the in-camera histogram is when shooting RAW. When the camera is set to JPEG it's pretty obvious what the histogram represents. But with RAW files, you don't get an actual image until you 'develop' the file. That's why the in-camera histograms are based on the JPEG images quickly developed by the camera in order to render a preview/thumbnail of the image. But a JPEG image is only an interpretation of the RAW data, and a very approximate one, especially when we are speaking of RGB histograms. And that's where my question comes in - how accurate is the in-camera histogram when shooting RAW? Can you rely on it as you can in the case of JPEG or should you treat it just as an estimate?

 

[tirediron]

The histogram isn't based on an image, it's based on the amount of light that is detected by each pixel of the sensor. The sensor converts that to an electric signal and the amplitude of that signal is what determines the histogram.

 

[Overread]

It's does suffer from the problems you outline, which is why when you shoot RAW its best to keep all your in camera auto editing settings set to neutral values. That way the default in camera editing is minimal and gives you a rough idea what the shot will look like. You might get a little more leeway at the overexposure end, but not much so it stands as a generally accurate way to measure the exposure when out in the field.

The only "perfect" way is to shoot tethered to a PC and review the RAWs right there and then, but that is not always possible to do so and can slow down your shooting considerably. For a studio it can be ideal - if you're out in the woods its not so practical

 

[Overread]

The histogram isn't based on an image, it's based on the amount of light that is detected by each pixel of the sensor. The sensor converts that to an electric signal and the amplitude of that signal is what determines the histogram.

I think the OP is talking about the histogram shown after a shot is taken whilst you're talking about the histogram produced during the use of liveview

 

[Drake]

The histogram isn't based on an image, it's based on the amount of light that is detected by each pixel of the sensor. The sensor converts that to an electric signal and the amplitude of that signal is what determines the histogram.

So what you're saying is that the histogram of an unedited RAW file is a 100% accurate representation of the luminosity, and not influenced by the camera's attempt to render a quick JPEG file?

I think the OP is talking about the histogram shown after a shot is taken whilst you're talking about the histogram produced during the use of liveview

I used to think they were actually the same, both representing an already rendered image, only that in LV it's being rendered in real time, and in the review mode it's rendered just once.

The only "perfect" way is to shoot tethered to a PC and review the RAWs right there and then, but that is not always possible to do so and can slow down your shooting considerably. For a studio it can be ideal - if you're out in the woods its not so practical

What difference does it make? Image rendered from the RAW data in camera or in post, it's still not representing the 'real' amount of light recorded by the camera.

I mean with a JPEG, you look at a histogram and know what's in there, how much of the image is overexposed etc. With a RAW file you don't really know until you try editing.

 

[Overread]

What I mean is a RAW image opened on your computer has all the light data without any modification - so all the light data is there - and if you set all the editing bars to 0 you have your base exposure.

However as I said you can't do that in the field every time - so you have your preview image generated after the shot is taken which is a processed JPEG (which is actually embedded inside your RAW and is what you see on the computer screen previews of the RAW shot). It's not 100% neutral but you can get pretty close with the default/neutral incamera editing settings.

 

[MohaimenK]

Overread is correct.

Remember, there are two types of Histogram informations. One is by the whole image, which is shown in black and white.

2nd type is the one in each color field R W and B

You can see both in your camera depending on which screen you are in.

But when you take the picture, if you pay attention to B&W version then it'll be the way to go. When you import it into your computer, it shows the individual channel which may make it a bit confusing for some. I know it did for me at first.

 

[Drake]

It's not 100% neutral but you can get pretty close with the default/neutral incamera editing settings.

I've got my Rebel XS set to the Standard picture style, there's also a Neutral setting but I haven't tried that. Or would it be best to just create a custom style and set everything to 0, as I never use JPEG anyway?

Still, it will probably do a pretty good job representing luminosity on a histogram. But what about RGB? It can differ a lot just because of the WB setting. I don't generally use the in-camera JPEG histogram, but it would be interesting to know how much you can rely on it.

 

[Overread]

White balance is a slightly separate issue with regard to the histogram, since you can control that directly with custom white balance to remove that possible flaw. However auto tends to do pretty well, though canon tend to be a little reddy and nikon a little more cool blue. However in general if you've got a neutral/normal editing setting on the JEPG and you've got overexposure shown in a colour channel, unless the auto white balance has been way off the mark (which you would see in the shot) you'll have overexposure in the RAW colour channel.

However colour channels are fiddly things - overexposure there is not as bad as in the luminescence and there are some cases where its almost unavoidable (try shooting yellow flowers close up without them overexposing in the red channel whilst also getting a good luminescence exposure)

 

[Boomn4x4]

There is no such thing as a RAW image. Only a RAW file. The RAW data does not have a histogram. When you are viewing a RAW file on your screen, your cameras software has already processed the image to some values that are either set by manual camera settings or automatically configured into the camera software.

The histogram you see on a RAW "file" is simply the histogram that comes from your basic camera processing.

 

[Drake]

There is no such thing as a RAW image. Only a RAW file. The RAW data does not have a histogram. When you are viewing a RAW file on your screen, your cameras software has already processed the image to some values that are either set by manual camera settings or automatically configured into the camera software.

The histogram you see on a RAW "file" is simply the histogram that comes from your basic camera processing.

That's exactly what I wrote in the first post, and why I asked how accurate the histogram usually was when shooting RAW.

 

[Boomn4x4]

There is no such thing as a RAW image. Only a RAW file. The RAW data does not have a histogram. When you are viewing a RAW file on your screen, your cameras software has already processed the image to some values that are either set by manual camera settings or automatically configured into the camera software.

The histogram you see on a RAW "file" is simply the histogram that comes from your basic camera processing.

That's exactly what I wrote in the first post, and why I asked how accurate the histogram usually was when shooting RAW.

They are as accurate as the software used to view the RAW damage is. Open the RAW file on different cameras and and different software packages and the histogram will be slightly different. Open a JPG on different cameras and differt packages and the histogram will be exactly the same.

I guess the answer to your question is that the histogram on a RAW file is just as accurate as a histogram of a JPG... just different.... If that makes sense.

I guess the best example I can think of is by looking at a "white" sheet of paper in a dark room using color light. The "color" of the light determines the color of the paper. Shine a incandescent light on it and it will be a different color than if you shine a halogen light on it which will be a different color than if you shine a black light on it. If you take a histogram of all of them, they will all be different.... but they will also all be accurate.

 

[Overread]

Slightly true - though with RAW files remember most RAW processing software will have its own default edit values when it opens a RAW (either its own or it reads them from your camera's default settings when opening the RAW). I would assume that if you take all the editing sliders in different RAW editing programs and set them to 0 values you would get the same histogram presentation

 

[Drake]

I would assume that if you take all the editing sliders in different RAW editing programs and set them to 0 values you would get the same histogram presentation

Not sure about that, I remember that when I looked at my images in Canon's DPP and compared to LR2, the noise had a noticeably different characteristics., even though the NR sliders were set to 0 in both cases. There's also a slight difference between LR2 and LR3. I suppose it means that every software interprets the RAW data differently, even with all the sliders set to 0.

 

[SlickSalmon]

I have the same question that Drake has been asking. Try as I might to follow this thread, I'm not able to tease out the answer from all the responses.

I've read several books on the Nikon 5000 that I'm using, and I still can't figure out what data the camera is using to display a histogram when the image is captured in RAW. Is it displaying a histogram of the 12-bit RAW file? If so, how is it doing that on a histogram screen that can only display 8-bit data? Is it doing a .jpg conversion first?