Exploring ETTR/EBTR
Oct 7, 2022 20:58:37 #
It seems that there is some confusion regarding ETTR/EBTR (Expose To The Right / Expose Beyond The Right respectively) techniques.
To start things off, we need to define a few terms. Understanding these terms will be important as we work on obtaining the optimum exposure for a photograph. Some of this is review for some and an introduction of terms to others.
Exposure -
Exposure = Intensity x Time
Intensity is how bright. Time is how long. That is pretty simple. We have the luminance of the scene and the length of time the shutter is open. That's it.
Sensitivity -
The response to light, preferably for this discussion, within the visible spectrum. This sensitivity is given a rating which is defined by the International Standards Organization (ISO) The greater the numerical value the more sensitive to light the material is.
Light Meter
A device, either built-in or hand-held, that measures the intensity of the light. The light meter is a very precise, but very dumb, piece of scientific equipment. By that I mean, it doesn't know what is being measured, dark or light, it doesn't know the end result we wish to photographically accomplish, it simply measures. That measurement produces a photographic exposure that places the measured value in middle gray. This equates to Zone V. This is rather important and should be kept in mind.
Zones-
Essentially, in photography, there are 11 zones of brightness. These zones are customarily referred to as Zone 0 through Zone X, using Roman numerals for 1 through 10. Zone 0 is black with no discernible details. Zone X is pure white, again with no discernible details. Zone X is reserved for featureless white, such as specular reflections. Zone V falls in the middle and referred to as middle gray.
Photographic Exposure -
For this discussion, I'd like to use the term Photographic Exposure as the combination of the Exposure, from the above definition, along with the sensitivity of the photo material to light. This will reduce the confusion over whether the technical term exposure is being referenced or the capture of photographic exposure is being discussed.
This adds a photosensitive material to the mix. Considering we are using a camera this material is in a light-tight box with a lens, iris, and shutter between it and the outside world. The sensitivity of the material enters into the mix of determining the photographic exposure. This is similar to balancing a beam scale. The combination of shutter-speed and f/stop is on one side, ISO is on the other. Given an ISO we need to adjust the Exposure in order to keep things balanced.
Additionally, a photographic exposure for middle gray is determined by the following rule. The basic f-stop is equal to the square root of the ISO and the basic shutter speed is equal to the reciprocal of the number of foot-candles measured. This is part of the magic light meters perform when measuring a scene. An ambient light meter averages all of the light values to produce the number of foot candles of the scene. Spot meters are a bit more specific as to what part of the scene they measure.
For example. If you are using ISO 125 and measuring a scene that is 200 foot-candles, the appropriate setting for a photographic exposure to render the measured part of the scene middle gray is f/11 (closest square root to 125) and 1/200 of a second. Fortunately, almost all of our light meters and cameras do all this calculating for us.
Histogram
A statistical chart or diagram consisting of rectangles whose area is proportional to the frequency of a variable and whose width is equal to the class interval. In photography, a histogram is a graphical representation of the tonal values of an image. The photographic histogram is a diagram whose horizontal axis is divided into 256 sections, numbered 0 through 255. 0 is pure black and 255 is pure white. The vertical axis simply indicates the number of pixels of a given tonal value.
Capture
The act of activating the shutter of a camera to allow a measured amount of light to strike a photosensitive material.
RAW
The data collected by the camera during the making of the Capture.
Dynamic Range
Dynamic range is the difference between the smallest and largest usable signal through a transmission or processing chain or storage medium. It is measured as a ratio or as a base-10 (decibel) or base-2 (doublings, bits, or stops) logarithmic value. In our use, it generally refers to the number of stops between the darkest and brightest a camera is capable of capturing.
Now that we have these concepts in mind, we have one more important aspect to consider. That is the camera's actual capability to capture bright details vs. the cameras programming to produce a jpg. We all should know that each capture we make produces a RAW file. The camera uses this RAW file to produce the image, which is previewed on the back of the digital camera. The camera also contains programming that will let us know if 'it thinks' the image we captured is overexposed. This is commonly denoted as blinkies. We are also under the concept that we should avoid having blinkies at all costs. But, what if that were not the case?
ETTR / EBTR
Now let's get to the discussion of ETTR and EBTR (Expose To The Right / Expose Beyond The Right respectively). First off, let's clear up the misconception that EBTR is over-exposure. It is not. If it were overexposed we would not be able to retrieve any information from that part of the image. The idea with ETTR is to expose such that the histogram reveals the image data is moved to the right as far as possible without clipping any of the data from the scene. The use of EBTR is to capture the scene where the histogram data shows some information is clipped, thus blinkies. The beyond the right part is in reference to the right of the camera-produced jpg image histogram.
Wait, didn't we just say we didn't want to lose image data? Yes, and we haven't. Remember. The image sensor captures and stores, in RAW, data that the camera produced jpg shows as blinkies. One possible reason for this is that the manufacturers want to play it a bit conservatively to insure the camera user gets far more 'good' pictures than not. For each additional stop of usable dynamic range we can use, we gain significant amounts more usable information for our image.
Unfortunately, each camera sensor has its own limits. This can vary even between cameras of the same model. To find out where they are, one must test their particular camera to make that determination. Thus, we have set the foundations for making optimum exposures.
For this discussion, I'm using a Nikon D800E. Through testing with a Macbeth Color Chart, I found that I can easily expose 2 to 2-1/2 stops beyond what my camera indicates for a spot-meter of the white square. To perform the test, I placed a Macbeth Color Chart in an evenly lit area. Metering on the white square, I increased my exposure until I could no longer retrieve, in processing, useful information from the white square. This provided me with the maximum number of additional stops., Thus, each of the Zones V through X is contained within those 2 to 2-1/2 stops.
So, now let's consider photographic exposure. There are three quantities that make up photographic exposure, shutter speed, f-stop, and ISO. Generally, the ISO is a fixed quantity. Although ISO can be adjusted from capture to capture, for the most part, it is a constant throughout a given series of captures. The other two variables are shutter speed and f-stop. These quantities are varied depending on whether one wants to capture motion or depth of field. The entire action of taking a photograph is somewhat of a system management exercise. Trade-offs have to be made.
Now let's work on the concept of getting the most out of each photographic exposure being made. To start with we have a light meter. For the best use of this feature, or tool, we are going to use spot metering. This measures a very small portion of the scene being photographed. Keep in mind that whatever part of the scene one measures, the meter returns a reading and suggested shutter speed/f-stop combination which will render that part of the scene middle gray.
For digital photography, as well as color film photography, the brightest part of the scene is the important one to consider. So, now I'll explain my technique for capturing the most usable data in a digital photograph.
How I expose for ETTR/EBTR
The following practice is based on a number of tests that ultimately determined my camera's exposure capabilities. It places all of the above into practice.
I will visually scan the scene which I intend to capture with my camera. I then spot meter the brightest part of that scene. My next decision is in which Zone I wish to place that highlight. If it's clouds, the brightest part may not be all that white. So, my first decision is to choose a Zone for the brightest part of the cloud. I'll spot meter that part of the cloud and then add stops to increase the brightness to the desired Zone, perhaps Zone VII or VIII, depending on the creative vision or intended use. I know from testing that I can process a photograph of a Macbeth Color Chart that is 2-1/2 stops past what the camera indicates as proper exposure when spot-metering the white square.
After making the capture, I will process the image in Photoshop ACR. In that process, I will make preliminary white balance adjustments and move the Exposure Slider to the negative side with an appropriate number of stops. That is the start of my processing. This is followed by adjusting the Highlights and Shadows sliders, followed by adjustment of the Whites and Blacks sliders. Adjusting overall contrast along with mid-range contrast finish the preliminary step and I'll transfer the image to Ps. Once there, I'll do an Image Specific hue contamination correction, burn and dodge, and a final processing step of applying a slight vignette centered on what I consider the primary interest of the photograph. Add a border and signature, and I'm done.
In conclusion, by increasing exposure, the goal of more accurate placement of the highlight areas of a scene in an appropriate Zone is accomplished. Blowing out highlights is avoided. An additional benefit of this pushing exposures to the right is that the process increases the amount of image data captured in the dark areas, as well. The unintended consequence of this additional information is that noise is made less visible.
--Bob
To start things off, we need to define a few terms. Understanding these terms will be important as we work on obtaining the optimum exposure for a photograph. Some of this is review for some and an introduction of terms to others.
Exposure -
Exposure = Intensity x Time
Intensity is how bright. Time is how long. That is pretty simple. We have the luminance of the scene and the length of time the shutter is open. That's it.
Sensitivity -
The response to light, preferably for this discussion, within the visible spectrum. This sensitivity is given a rating which is defined by the International Standards Organization (ISO) The greater the numerical value the more sensitive to light the material is.
Light Meter
A device, either built-in or hand-held, that measures the intensity of the light. The light meter is a very precise, but very dumb, piece of scientific equipment. By that I mean, it doesn't know what is being measured, dark or light, it doesn't know the end result we wish to photographically accomplish, it simply measures. That measurement produces a photographic exposure that places the measured value in middle gray. This equates to Zone V. This is rather important and should be kept in mind.
Zones-
Essentially, in photography, there are 11 zones of brightness. These zones are customarily referred to as Zone 0 through Zone X, using Roman numerals for 1 through 10. Zone 0 is black with no discernible details. Zone X is pure white, again with no discernible details. Zone X is reserved for featureless white, such as specular reflections. Zone V falls in the middle and referred to as middle gray.
Photographic Exposure -
For this discussion, I'd like to use the term Photographic Exposure as the combination of the Exposure, from the above definition, along with the sensitivity of the photo material to light. This will reduce the confusion over whether the technical term exposure is being referenced or the capture of photographic exposure is being discussed.
This adds a photosensitive material to the mix. Considering we are using a camera this material is in a light-tight box with a lens, iris, and shutter between it and the outside world. The sensitivity of the material enters into the mix of determining the photographic exposure. This is similar to balancing a beam scale. The combination of shutter-speed and f/stop is on one side, ISO is on the other. Given an ISO we need to adjust the Exposure in order to keep things balanced.
Additionally, a photographic exposure for middle gray is determined by the following rule. The basic f-stop is equal to the square root of the ISO and the basic shutter speed is equal to the reciprocal of the number of foot-candles measured. This is part of the magic light meters perform when measuring a scene. An ambient light meter averages all of the light values to produce the number of foot candles of the scene. Spot meters are a bit more specific as to what part of the scene they measure.
For example. If you are using ISO 125 and measuring a scene that is 200 foot-candles, the appropriate setting for a photographic exposure to render the measured part of the scene middle gray is f/11 (closest square root to 125) and 1/200 of a second. Fortunately, almost all of our light meters and cameras do all this calculating for us.
Histogram
A statistical chart or diagram consisting of rectangles whose area is proportional to the frequency of a variable and whose width is equal to the class interval. In photography, a histogram is a graphical representation of the tonal values of an image. The photographic histogram is a diagram whose horizontal axis is divided into 256 sections, numbered 0 through 255. 0 is pure black and 255 is pure white. The vertical axis simply indicates the number of pixels of a given tonal value.
Capture
The act of activating the shutter of a camera to allow a measured amount of light to strike a photosensitive material.
RAW
The data collected by the camera during the making of the Capture.
Dynamic Range
Dynamic range is the difference between the smallest and largest usable signal through a transmission or processing chain or storage medium. It is measured as a ratio or as a base-10 (decibel) or base-2 (doublings, bits, or stops) logarithmic value. In our use, it generally refers to the number of stops between the darkest and brightest a camera is capable of capturing.
Now that we have these concepts in mind, we have one more important aspect to consider. That is the camera's actual capability to capture bright details vs. the cameras programming to produce a jpg. We all should know that each capture we make produces a RAW file. The camera uses this RAW file to produce the image, which is previewed on the back of the digital camera. The camera also contains programming that will let us know if 'it thinks' the image we captured is overexposed. This is commonly denoted as blinkies. We are also under the concept that we should avoid having blinkies at all costs. But, what if that were not the case?
ETTR / EBTR
Now let's get to the discussion of ETTR and EBTR (Expose To The Right / Expose Beyond The Right respectively). First off, let's clear up the misconception that EBTR is over-exposure. It is not. If it were overexposed we would not be able to retrieve any information from that part of the image. The idea with ETTR is to expose such that the histogram reveals the image data is moved to the right as far as possible without clipping any of the data from the scene. The use of EBTR is to capture the scene where the histogram data shows some information is clipped, thus blinkies. The beyond the right part is in reference to the right of the camera-produced jpg image histogram.
Wait, didn't we just say we didn't want to lose image data? Yes, and we haven't. Remember. The image sensor captures and stores, in RAW, data that the camera produced jpg shows as blinkies. One possible reason for this is that the manufacturers want to play it a bit conservatively to insure the camera user gets far more 'good' pictures than not. For each additional stop of usable dynamic range we can use, we gain significant amounts more usable information for our image.
Unfortunately, each camera sensor has its own limits. This can vary even between cameras of the same model. To find out where they are, one must test their particular camera to make that determination. Thus, we have set the foundations for making optimum exposures.
For this discussion, I'm using a Nikon D800E. Through testing with a Macbeth Color Chart, I found that I can easily expose 2 to 2-1/2 stops beyond what my camera indicates for a spot-meter of the white square. To perform the test, I placed a Macbeth Color Chart in an evenly lit area. Metering on the white square, I increased my exposure until I could no longer retrieve, in processing, useful information from the white square. This provided me with the maximum number of additional stops., Thus, each of the Zones V through X is contained within those 2 to 2-1/2 stops.
So, now let's consider photographic exposure. There are three quantities that make up photographic exposure, shutter speed, f-stop, and ISO. Generally, the ISO is a fixed quantity. Although ISO can be adjusted from capture to capture, for the most part, it is a constant throughout a given series of captures. The other two variables are shutter speed and f-stop. These quantities are varied depending on whether one wants to capture motion or depth of field. The entire action of taking a photograph is somewhat of a system management exercise. Trade-offs have to be made.
Now let's work on the concept of getting the most out of each photographic exposure being made. To start with we have a light meter. For the best use of this feature, or tool, we are going to use spot metering. This measures a very small portion of the scene being photographed. Keep in mind that whatever part of the scene one measures, the meter returns a reading and suggested shutter speed/f-stop combination which will render that part of the scene middle gray.
For digital photography, as well as color film photography, the brightest part of the scene is the important one to consider. So, now I'll explain my technique for capturing the most usable data in a digital photograph.
How I expose for ETTR/EBTR
The following practice is based on a number of tests that ultimately determined my camera's exposure capabilities. It places all of the above into practice.
I will visually scan the scene which I intend to capture with my camera. I then spot meter the brightest part of that scene. My next decision is in which Zone I wish to place that highlight. If it's clouds, the brightest part may not be all that white. So, my first decision is to choose a Zone for the brightest part of the cloud. I'll spot meter that part of the cloud and then add stops to increase the brightness to the desired Zone, perhaps Zone VII or VIII, depending on the creative vision or intended use. I know from testing that I can process a photograph of a Macbeth Color Chart that is 2-1/2 stops past what the camera indicates as proper exposure when spot-metering the white square.
After making the capture, I will process the image in Photoshop ACR. In that process, I will make preliminary white balance adjustments and move the Exposure Slider to the negative side with an appropriate number of stops. That is the start of my processing. This is followed by adjusting the Highlights and Shadows sliders, followed by adjustment of the Whites and Blacks sliders. Adjusting overall contrast along with mid-range contrast finish the preliminary step and I'll transfer the image to Ps. Once there, I'll do an Image Specific hue contamination correction, burn and dodge, and a final processing step of applying a slight vignette centered on what I consider the primary interest of the photograph. Add a border and signature, and I'm done.
In conclusion, by increasing exposure, the goal of more accurate placement of the highlight areas of a scene in an appropriate Zone is accomplished. Blowing out highlights is avoided. An additional benefit of this pushing exposures to the right is that the process increases the amount of image data captured in the dark areas, as well. The unintended consequence of this additional information is that noise is made less visible.
--Bob
Oct 7, 2022 21:29:49 #
rmalarz wrote:
To perform the test, I placed a Macbeth Color Chart in an evenly lit area. Metering on the white square, I increased my exposure until I could no longer retrieve, in processing, useful information from the white square. This provided me with the maximum number of additional stops., Thus, each of the Zones V through X is contained within those 2 to 2-1/2 stops.
Bob, can you please explain the 'method' you used in ACR processing that determined that no useful information could be retrieved from the white square.
Oct 7, 2022 21:34:46 #
Simply, it's a matter of moving the Exposure slider as far to the left as possible. At that point, the white square was still at 255 and the colors of the other squares were nowhere close to what they should have been.
--Bob
--Bob
Grahame wrote:
Bob, can you please explain the 'method' you used in ACR processing that determined that no useful information could be retrieved from the white square.
Oct 8, 2022 00:17:28 #
Bob, thanks for the detailed explanation of this often misunderstood and useful procedure. Your work (and that of other excellent photographers on the forum) that use this technique to utilize all the dynamic range your camera is capable of is proof of its efficacy.
Oct 8, 2022 00:19:56 #
Thanks, TriX. I appreciate your visit and comment.
--Bob
--Bob
TriX wrote:
Bob, thanks for the detailed explanation of this often misunderstood and useful procedure. Your work (and that of other excellent photographers on the forum) that use this technique to utilize all the dynamic range your camera is capable of is proof of its efficacy.
Oct 8, 2022 06:56:55 #
Bob, thanks for this and thanks for sending it to be personally a few weeks back. I've barely skimmed through it at the mo. but along with other comments have seen an improvement in my black and white work.
That's not to say the images are good but they're looking better than had I followed my previous method.
That's not to say the images are good but they're looking better than had I followed my previous method.
Oct 8, 2022 07:01:14 #
Bob, you have offered an excellent explanation of the whole process of ETTR and its benefits. I am afraid your explanation is too complicated and confusing for the young photographer who is not familiar with the zone system of Ansel Adams, who during the film era put lots of emphasis on exposing for the important dark areas. At the time, as you know very well the development of the film regulated the brightness of the highlights when it came to b&w photography.
The spot meter is a super precise instrument in the hands of the knowledgeable photographer. Today practically all cameras made have a spot meter built-in but I bet a majority of the photographers here use matrix or evaluative metering instead. Matrix is pretty good but many times it fails miserably and the reason could be that it depends heavily on where the selected sensor for AF is placed on a scene. Because the exposure is automatically compensated we are in the dark till we interpret the histogram. Matrix does not always exposes properly or accurately for the highlights and as you know if the important highlight is not well exposed with digital then clipping will occur ruining the image. When I use matrix in sunlight I am usually setting my camera at 1 stop underexposure and that has worked for me. Someone's else camera could be different.
Indeed a spot meter is a very precise instrument of measurement. As you said and, I am sure a majority here knows, exposure meters read middle tonalities, so called gray tone. Black or white are not middle tones so they require an adjustment of the exposure. Experimenting is cheap with digital so my recommendation is that a photographer should learn how his or her camera meter works and when to intervene to make the exposure accurate. In the case of a bright subject it is about 2 stops of light for cameras with a good brightness range. That, as you mentioned, is the equivalent of a zone VII using the Ansel Adams zone system. With my camera I usually go with zone VI and when necessary I add some brightness in post. Never a blown highlight when I have done so.
We are fortunate having cameras today that have a dynamic range wider than film used to have. Using the zone system we are more in control although the procedure takes time and it is not suitable for all subjects. It is especially useful for the landscape photographer but less so for wildlife or action when timing makes the difference to get the shot.
In short, chances are excellent when using digital that if we take an accurate reading of an important highlight and we expose properly those highlights will hold all of the details present. As we get the highlights properly exposed all other tonalities will fall in place.
Thank you for taking the time to post this and for your excellent explanations.
The spot meter is a super precise instrument in the hands of the knowledgeable photographer. Today practically all cameras made have a spot meter built-in but I bet a majority of the photographers here use matrix or evaluative metering instead. Matrix is pretty good but many times it fails miserably and the reason could be that it depends heavily on where the selected sensor for AF is placed on a scene. Because the exposure is automatically compensated we are in the dark till we interpret the histogram. Matrix does not always exposes properly or accurately for the highlights and as you know if the important highlight is not well exposed with digital then clipping will occur ruining the image. When I use matrix in sunlight I am usually setting my camera at 1 stop underexposure and that has worked for me. Someone's else camera could be different.
Indeed a spot meter is a very precise instrument of measurement. As you said and, I am sure a majority here knows, exposure meters read middle tonalities, so called gray tone. Black or white are not middle tones so they require an adjustment of the exposure. Experimenting is cheap with digital so my recommendation is that a photographer should learn how his or her camera meter works and when to intervene to make the exposure accurate. In the case of a bright subject it is about 2 stops of light for cameras with a good brightness range. That, as you mentioned, is the equivalent of a zone VII using the Ansel Adams zone system. With my camera I usually go with zone VI and when necessary I add some brightness in post. Never a blown highlight when I have done so.
We are fortunate having cameras today that have a dynamic range wider than film used to have. Using the zone system we are more in control although the procedure takes time and it is not suitable for all subjects. It is especially useful for the landscape photographer but less so for wildlife or action when timing makes the difference to get the shot.
In short, chances are excellent when using digital that if we take an accurate reading of an important highlight and we expose properly those highlights will hold all of the details present. As we get the highlights properly exposed all other tonalities will fall in place.
Thank you for taking the time to post this and for your excellent explanations.
Oct 8, 2022 07:34:42 #
Bob - thank you for this excellent and detailed post. What are your thoughts concerning highlight metering?
Oct 8, 2022 08:07:39 #
rmalarz wrote:
It seems that there is some confusion regarding ET... (show quote)
Very good article.
You made it clear once through the technical first part.
Oct 8, 2022 09:33:40 #
rmalarz wrote:
It seems that there is some confusion regarding ET... (show quote)
Thank You for this really good explanation of a subject I was still a little unsure about. Do you mind if I share with my sister and niece who have just entered the arena of photography?
Oct 8, 2022 10:02:27 #
Oct 8, 2022 10:39:30 #
Oct 8, 2022 11:17:37 #
rmalarz wrote:
It seems that there is some confusion regarding ET... (show quote)
I normally hate long, multi-paragraph postings. My attention span just can not deal. But I absorbed every line here. Why? Because I learned something that will make me a better photographer.
Thank you!
Oct 8, 2022 11:41:15 #
rmalarz wrote:
It seems that there is some confusion regarding ET... (show quote)
Bob. Great written article. Very well done and explained. It explains the system will and how you used it to fine tune it to your camera. It also shows how your photos are always so good. Thank you for taking the time to write and share this. I thought I understood this, but I was not aware you could go THAT FAR RIGHT and still recover.
Oct 8, 2022 12:02:07 #
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