cinematography RGB histogram
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Thats an interesting question. It seems like an esoteric production technical detail, and I wonder why a director would care. The Histogram, and all other exposure aids are there to help get the best image POSSIBLE, maximize dynamic range etc. This is what the DP is supposed to be worried about. If the director doesn't trust, rightly or wrongly, in the DP then its up to the director to make sure the technical aspects are covered..
If your talking POST then Id say, the scopes are for color CORRECTION, and desired look has nothing to do with it. The next layer of color GRADING for look is where the director has ALL the say.
If your talking POST then Id say, the scopes are for color CORRECTION, and desired look has nothing to do with it. The next layer of color GRADING for look is where the director has ALL the say.
As far as I know this has to do with legal broadcast colors. For example, a red sweater is so saturated with red it exceeds broadcast limits and must be toned down below 100%. In my old job this was handled by engineers that would adjust the image during live broadcasts, but with modern day NLE's it relates to additional post production being necessary prior to distribution...I think.
In any case, it's a post thing and you don't want to peg colors (RGB=red, green, blue) as that will make the image all out of color balance. An exposure histogram is a different animal.
In any case, it's a post thing and you don't want to peg colors (RGB=red, green, blue) as that will make the image all out of color balance. An exposure histogram is a different animal.
Hmm interesting stuff 
Thanks guys! CamVader, youve kind of lost me there, sorry.
And I wasn't refering to POST, but live on set. I noticed if I want a more darker image, Id try to hit the exposure down, thus, the RGB histogram would be showing a spike on the left side of the histogram.
However, I was thinking, would it be better, to have the spike in the middle of the histogram, cause they, say its optimum, and THEN...grade colors in post-production, crush blacks for a darker image etc.?
Thanks guys! CamVader, youve kind of lost me there, sorry. And I wasn't refering to POST, but live on set. I noticed if I want a more darker image, Id try to hit the exposure down, thus, the RGB histogram would be showing a spike on the left side of the histogram.
However, I was thinking, would it be better, to have the spike in the middle of the histogram, cause they, say its optimum, and THEN...grade colors in post-production, crush blacks for a darker image etc.?
If you've moved the lump that far to the right so that it is roughly centered, then you are likely clipping highlights. In video it's easier to pull up shadow detail than it is to restore clipped regions in bright parts of the frame - hence exposures on an RGB histogram seem to be weighted on the left hand side of the scale.
At least that's been my general understanding.
It's easier for me to read false color than it is for me to read histograms still. Once my GH2 gets here I'll have a lot more opportunity for subtle testing of things. No chance to do that sort of esoteric stuff while I'm working.
Double Edit:
If the director has a reason to question the DP's ability to expose the image, it might be time to explore new options in staffing. Otherwise histograms should be pretty low on a director's list of priorities - he/she should be able to take as a given that the DP knows the exposure needed for the desired end image that results in minimal work and/or problems in post.
IMNSHO.
At least that's been my general understanding.
It's easier for me to read false color than it is for me to read histograms still. Once my GH2 gets here I'll have a lot more opportunity for subtle testing of things. No chance to do that sort of esoteric stuff while I'm working.
Double Edit:
If the director has a reason to question the DP's ability to expose the image, it might be time to explore new options in staffing. Otherwise histograms should be pretty low on a director's list of priorities - he/she should be able to take as a given that the DP knows the exposure needed for the desired end image that results in minimal work and/or problems in post.
IMNSHO.
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Hmm interesting stuff
And I wasn't refering to POST, but live on set. I noticed if I want a more darker image, Id try to hit the exposure down, thus, the RGB histogram would be showing a spike on the left side of the histogram.
However, I was thinking, would it be better, to have the spike in the middle of the histogram, cause they, say its optimum, and THEN...grade colors in post-production, crush blacks for a darker image etc.?
Sorry. Check this out: http://www.cambridgeincolour.com/tutorials/histograms2.htm
Middle is better for what you are looking for.
@ David - what do you mean clipping highlights? Im not sure what does that mean
So youre saying it it reads better when the spike is towards the left, correct me if im wrong. Oh, and what do you mean by "It's easier for me to read false color than it is for me to read histograms still"?
So youre saying it it reads better when the spike is towards the left, correct me if im wrong. Oh, and what do you mean by "It's easier for me to read false color than it is for me to read histograms still"?
Clipping just means you are loosing information in the image because it is all blowing out to pure white. Loosing highlight detail.
False color is another exposure tool in some monitors. Color codes different parts of an image to correspond roughly to ... ire values, I think ... Usually expressed as a 0-100 scale, so probably ire.
The photography tutorials are great, but there is something different about the histograms that I see while working on cams like EX, RED, HVX, HDX, etc. The curve is generally left justified while retaining data across the board without a spike at either end. I don't have a way to express why, but there it is. The DPs I'm working under are getting the exposure they want and checking histograms. Perhaps someday I'll be able to write some long winded, pedantic explanation. 
False color is another exposure tool in some monitors. Color codes different parts of an image to correspond roughly to ... ire values, I think ... Usually expressed as a 0-100 scale, so probably ire.
The photography tutorials are great, but there is something different about the histograms that I see while working on cams like EX, RED, HVX, HDX, etc. The curve is generally left justified while retaining data across the board without a spike at either end. I don't have a way to express why, but there it is.
The DPs I'm working under are getting the exposure they want and checking histograms. Perhaps someday I'll be able to write some long winded, pedantic explanation.
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If you can find a director who understands a histogram I'll be very impressed. I don't see why they'd need to if they have a competent DoP - they might want the picture to be brighter or darker to taste, but reasons for or against that should be explained to them rather than leaving them to (mis)interpret graphs.
It looks like we're talking about a luma histogram for exposure. The RGB will indicate color cast. I learned something today.
The Histogram
The Histogram provides a very different type of analysis than the waveform-based scopes. Whereas waveforms have a built-in correspondence between the horizontal position of the image being analyzed and that of the waveform graph, histograms provide a statistical analysis of the image.
Histograms work by calculating the total number of pixels of each color or luma level in the image and plotting a graph that shows the number of pixels there are at each percentage. It’s really a bar graph of sorts, where each increment of the scale from left to right represents a percentage of luma or color, while the height of each segment of the histogram graph shows the number of pixels that correspond to that percentage.
The RGB Histogram
The RGB histogram display shows separate histogram analyses for each color channel. This lets you compare the relative distribution of each color channel across the tonal range of the image.
For example, images with a red color cast have either a significantly stronger red histogram, or conversely, weaker green and blue histograms. In the following example, the red cast in the highlights can be seen clearly.
The R, G, and B Histograms
The R, G, and B histograms are simply isolated versions of each channel’s histogram graph.
The Luma Histogram
The Luma histogram shows you the relative strength of all luminance values in the video frame, from black to super-white. The height of the graph at each step on the scale represents the number of pixels in the image at that percentage of luminance, relative to all the other values. For example, if you have an image with few highlights, you would expect to see a large cluster of values in the Histogram display around the midtones.
The Luma histogram can be very useful for quickly comparing the luma of two shots so you can adjust their shadows, midtones, and highlights to match more closely. For example, if you were matching a cutaway shot to the one shown above, you can tell just by looking that the image below is underexposed, but the Histogram gives you a reference for spotting how far.
The shape of the Histogram is also good for determining the amount of contrast in an image. A low-contrast image, such as the one shown above, has a concentrated clump of values nearer to the center of the graph. By comparison, a high-contrast image has a wider distribution of values across the entire width of the Histogram.
The Histogram
The Histogram provides a very different type of analysis than the waveform-based scopes. Whereas waveforms have a built-in correspondence between the horizontal position of the image being analyzed and that of the waveform graph, histograms provide a statistical analysis of the image.
Histograms work by calculating the total number of pixels of each color or luma level in the image and plotting a graph that shows the number of pixels there are at each percentage. It’s really a bar graph of sorts, where each increment of the scale from left to right represents a percentage of luma or color, while the height of each segment of the histogram graph shows the number of pixels that correspond to that percentage.
The RGB Histogram
The RGB histogram display shows separate histogram analyses for each color channel. This lets you compare the relative distribution of each color channel across the tonal range of the image.
For example, images with a red color cast have either a significantly stronger red histogram, or conversely, weaker green and blue histograms. In the following example, the red cast in the highlights can be seen clearly.
The R, G, and B Histograms
The R, G, and B histograms are simply isolated versions of each channel’s histogram graph.
The Luma Histogram
The Luma histogram shows you the relative strength of all luminance values in the video frame, from black to super-white. The height of the graph at each step on the scale represents the number of pixels in the image at that percentage of luminance, relative to all the other values. For example, if you have an image with few highlights, you would expect to see a large cluster of values in the Histogram display around the midtones.
The Luma histogram can be very useful for quickly comparing the luma of two shots so you can adjust their shadows, midtones, and highlights to match more closely. For example, if you were matching a cutaway shot to the one shown above, you can tell just by looking that the image below is underexposed, but the Histogram gives you a reference for spotting how far.
The shape of the Histogram is also good for determining the amount of contrast in an image. A low-contrast image, such as the one shown above, has a concentrated clump of values nearer to the center of the graph. By comparison, a high-contrast image has a wider distribution of values across the entire width of the Histogram.
Thanks Vader.
I knew the axes (plural of axis?) on the RGB on, it was the Luma histogram I'm not used to looking at - most of the time on set it's either an RGB histogram, or one of the "scope" style tools.
It was the Luma one that was confusing me. Luma graph lumps are indicating something slightly different than RGB ones - so it makes a little more sense that the target might be farther right than I am used to in many cases.
I knew the axes (plural of axis?) on the RGB on, it was the Luma histogram I'm not used to looking at - most of the time on set it's either an RGB histogram, or one of the "scope" style tools.
It was the Luma one that was confusing me. Luma graph lumps are indicating something slightly different than RGB ones - so it makes a little more sense that the target might be farther right than I am used to in many cases.
I'm going to get this info down somehow.
It turns out when I was yammering about legal broadcast colors in an earlier post, I was really talking about a vectorscope and didn't know any better.
Luma is really cool because it gives highlights information. I'm starting to really like cinematography for the mad scientist potential.
hey CaVader, can you inline those pics referenced in your post?
Sure, man. I should have provided the link in the first place.
http://documentation.apple.com/en/color/usermanual/index.html#chapter=8§ion=3&tasks=true