Capture One Histograms are a powerful tool to judge your image edits. Paired with the Levels Tool, you can accomplish a lot with very few controls. The simple Levels Tool is ideal for setting image black and white points as well as controlling the overall character of an image. Using the Levels Tool well requires a firm understanding of histograms and how images are processed in Capture One. A little knowledge will speed up your editing process and remove uncertainty.
I previously wrote a blog post about using the Levels Tool that covers it’s basic usage. It is worth checking out too if you haven’t read it. This post goes a little deeper on what is happening and how to use the histogram to determine your black, white and mid points.
Capture One Histograms: Source and Output
Before we talk in detail about levels, we need to make sure everyone is on the same page about histograms and the image processing pipeline.
In Capture One, the Histogram Tool shows you the output histogram of the entire image processing pipeline. That is, it shows you the histogram of the resulting image you see in the large image viewer.
Understanding a Histogram
The left hand edge of the histogram represents black, the right hand edge represents white with the values between left and right going from almost black to almost white. That is, you can think of the columns in the histogram as each representing a grey level, or a “brightness” or a tone. They are all words for the same thing. For now, only look at the grey graph. You can safely ignore the Red, Green and Blue graphs for now.
The histogram simplifies the image getting rid of information about where pixels are, and instead showing you the proportions of light and dark in the image.
So, what is an input (source) histogram, and what is an output histogram? You (or rather software, given that there are millions of pixels in modern images) can calculate a histogram for any image: a camera RAW file, a straight-out-of-camera JPG or a finished fully retouched completed image.
The Image Editing Pipeline
When we edit a raw file, there are distinct steps in the image processing pipeline. Think of the image processing pipeline as a conveyor through a factory. Each stop on the conveyor has a machine to do one specific task. One of the very first stops on the conveyor is the white balance adjustment, for example. Later on down the conveyor (later in the pipeline) are other machines: exposure, clarity, etc.
When Phase One developed Capture One, they built that conveyor and put the machines along it in a specific fixed order. Other RAW processors are have their own fixed image processing pipelines too. For now, we aren’t going to worry about the specifics of the entire conveyor, but it is important to understand that an image is processed in specific stages, just like a car being built step by step in a factory. You can’t install the car’s interior before you welded its frame together. Processing a RAW file is no different.
Put your underwear on before your pants!
When you adjust the Levels Tool, it receives a source image on the conveyor from some previous adjustment tool (don’t worry about which one right now). The Levels Tool will change the image (if you have adjusted the level’s settings at all), and therefore change it’s histogram. So, the images that comes to the Levels machine has one histogram. Call this the “input histogram.” The image that leaves the Level Tool has (potentially) different histogram. Call this the output histogram.
So, the Input Histogram is the histogram of the source for an adjustment tool and the Output Histogram is the histogram of the result of the adjustment tool. If the tool’s controls are set to “0” (i.e. not adjusted), in most cases the input and output histogram are the same.
The Levels Histograms
In most cases we can’t see a tool’s specific input or output histograms… We only see the final output histogram of the entire process in the Histogram tool in Capture One. In the case of Levels Tool (and also the Curves) shows us the input histogram.
The histogram displayed under the controls in the Levels Tool is the Input Histogram for that tool. You can’t directly see the output histogram for these tools, but you can see their effect on the overall output histogram in the Capture One Histogram Tool.
Notice how the unadjusted levels on the left displays the same histogram as the Histogram Tool below it. That is because we haven’t adjusted the levels so that tool is not changing the image, and therefore, not changing the histogram. The right hand example shows adjusting the black point, and the main Histogram Tool shows the results of that adjustment. The main histogram is pushed up against the left hand side as we clip a lot of the shadow tones to black.
The Levels Tool
The levels tool allows you to do a number of things:
- Pick a black point and white point.
- Set a mid point.
- Choose the output “black” and “white” level.
I use #1 and #2 all the time and almost never use #3 and we are going to ignore it here since it has a specific special use case that you probably won’t run into. Lets explore the affect the other controls have on the overall histogram.
For more information on the mechanics of the controls, check out this point.
The black point determines where on the histogram pixels are full black. Any pixels in the source histogram darker than (i.e. to the left of) the black point value you choose will become full black. Sometimes we say we are clipping it to black. Lets look at a couple of examples.
Notice that the right hand image with the black point set at 39 has large swatches of black, and also that the rest of the image is darker with noticeable color shifts. Looking at the histogram for that image, you can see that the shape of the histogram on the right (the bright side) hasn’t changed but that the entire thing is stretched towards the left with the end smashed up against the black (left) side.
If we go a step further, and set the black point to 142, you can see that most of the image is black or very dark. That isn’t surprising if you consider that 142 is more than half way towards full white (Capture One uses a 0 to 255 scale, so half way is 127). We’ve made half the possible input values black and Capture One has stretched the rest out to fill the histogram. You can see that the shape of the right (bright) side of the original (source) histogram is still there but stretched out to fill the entire main Histogram Tool with a huge spike against the left side.
We’ve used the Levels Tool to clip most of the tones in the image to black. You probably wouldn’t want to do this on an actual image, but it is instructive to see the effect it has on the histogram.
Changing the White Point works identically to adjusting the black point except from the right hand, white, side of the histogram. You can choose the input tone (brightness, grey level) that becomes white. Everything to the right of that is “clipped” to white.
This image was shot protected the highlights (that is, so the histogram isn’t smashed up against the right side) so it is a little under exposed. Setting the white point to 176 mostly fixes the exposure, but it also starts to clip some of the highlights to white, particularly in the sky. You can see this happen in the main Histogram Tool as well. Some highlights are becoming full white since there is a spike against the right side.
When taken to extremes, you can see that the entire sky is white or nearly white. As with the extreme black point example, you will also start to get color shifts in the image.
Unlike the black and white points, the mid point shouldn’t change which tones get clipped to white or black. It changes the balance of the image and can shift the center of mass of the histogram either direction. Moving the mid point to the right (towards bright) in the levels tool makes the image seem darker. You are instructing Capture One to shift more of the source histogram to the left of the mid point, towards the dark side.
Moving the mid point left (towards the dark side) has the opposite effect and lightens the image.
The mid point can be thought of as a way to control the overall tonality of the image. It doesn’t affect what is clipped to black or white, but it does affect where most of the pixels live on the histogram. You can force them to the right or left or towards the center by dragging the mid point to the appropriate spot on the source histogram.
Picking Your Points
I started this blog post with a discussion of the image processing pipeline and histograms. Hopefully you’ve started to get a feel for how the Levels Tool allows you to directly manipulate your final main output Histogram. When I edit an image, I do a lot of the work in the Levels Tool. In fact, in the simplest form, my editing mostly involves auto adjusting and then picking a Levels Tool Mid Point.
Black and White Foundation
For this image, I’m going to edit it manually only using the levels tool just to show off the power. The first step is to pick black and white points. When choosing the white point, I normally want to preserve my highlight details. In this case the clouds are very bright and I don’t want any large blocks of white, but there should be some full white. For this image, I chose a white point of 188 that just clips off the right hand side of the input histogram. Like the white point, I don’t want any large splotches of black for this image. Choosing a black point of 8 just clips off the left hand side of the input histogram.
Exposure Warnings Help
One easy way to see what is nearly full white or black, if the histogram isn’t giving you enough information, is to enable exposure warnings by pressing Command-E (Mac) or Ctrl-E (PC). Exposure warnings highlights any nearly white pixels in red and any nearly black pixels in blue. You can adjust the thresholds for “nearly” black or white in the preferences. By default, they are set to 4 for black and 250 for white.
Mid Point Lighten Up
To my eye, this feels a little dark. The shadows on the rocks are to close to black. I can easily fix this by dragging the mid point to the left shifting more of the histogram to the right (bright) side. I chose a value of .2 for the mid point. This version looks about like I envisioned the photo.
And finally, here is the full histogram progression from unedited to finished Levels Tool only edit.
He is a self taught experiential learner who is addicted to the possibilities that new (to him) gear open up. He loves to share the things he has worked out. Andrew started with a passion for landscape and night photography and quickly branched out to work in just about every form of photography. He is an ex-software developer with extensive experience in the IT realm.