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2.2 Baseline Exposure and Contrast

Before you dig into making your photo look great, you need a flat, well-exposed image. Neutralized images let you evaluate everything consistently and plan your work. We will also take a look at the color adjustment tools within RawTherapee, how to read a histogram, and how to adjust our image’s exposure, contrast, highlights and shadows.

2.2 Baseline Exposure and Contrast

In this lesson, we'll talk about the importance of producing flat, well exposed images, so that you can evaluate everything equally and how to use a histogram to help you to do this. We'll also take a look at the color adjustment tools within RawTherapee and learn how to adjust our images exposure, contrast, highlights and shadows. So first, let's talk about why we want to correct our images, so that they're simply neutral. When you're editing a group of photos, the point of the quick light edits in the initial stage is to get the photos to a neutral standpoint. So that you know which ones are the best, which ones you want to discard and how far you will eventually want to push them stylistically. In this initial stage of editing, you want your photos to be not too anything. With the end result being a flat, well exposed image, so that you can evaluate a group or series of images together equally. This keeps the style of your group of images consistent. Next, let's chat about how to read a histogram in order to help us in this corrective process. When used correctly, a histogram can be an extremely useful tool in correcting the exposure of your images. So within RawTherapee first, lets close the top panel by selecting this button on the right hand side and now let's look at our image's histogram in the upper left. The histogram shows the concentration of pixels that are in the black, white and gray spectrum. The black information is on the left, the middle of a histogram is roughly 18% gray and the white pixel information is on the right-hand side. And so looking at this particular histogram, we can view the concentration of pixels for our image and you're also able to view your images separate channels by selecting these buttons on the left-hand side. So selecting the red button hides the red channels and selecting it again, shows it and so on for each channel and this final channel is the luminance histogram. And so looking at this particular histogram for our image, we see that it's decently exposed already. There's a generally even distribution of pixel information across the histogram. Let's briefly talk about clipping. Clipping can occur on either end of the spectrum on the histogram. Clipping is when information in your highlights or shadows gets cut off, you can tell when information is being clipped when either end of your histogram has no pixel information in it. Your highlights are on the right side and your shadows are on the left side. When this occurs, it's necessary to adjust the exposure of your image. Just a quick note, it's important to keep in mind that a skewed histogram can be okay if the style you are trying to achieve calls for it. For example, a high contrast photo could have a histogram that displays information that is not necessarily evenly distributed. It all depends on what you want your end result to be and so let's make some basic baseline exposure and contrast corrections to our image. And keep in mind as we make changes, the first window in the center pane will automatically update, so that it reflects the immediate previous state of the image and so the image on the right-hand side will be the most up to date. So both images will dynamically change as we make adjustments. Let's head over to the exposure tab, which is the first icon in our line of tools. We'll go ahead and select exposure and then we'll head to the exposure drop-down. Now the first thing you'll notice is the Auto Levels button and it may already be selected for you. This automatically adjusts your image and moves the set up sliders below based on an analysis of your photo. Sometimes, it does a good job. Other times it takes a little far, it really depends on your goal for the image. In this case, we wanna make our adjustments manually. So we're going to neutralize our image by selecting the neutral button on the right-hand side and this takes us to our starting point, viewable here in the right-hand image. So let's make some manual adjustments. First, we have the exposure compensation slider, which is equivalent to adjusting the ISO. And so when we drag the slider to the right, you'll notice that it's essentially increasing the exposure of our image. Now when you set exposure too high, you begin to lose vital information in the highlights. And if you look at our histogram in the upper left, you'll see that some clipping is occurring where information on the left side of the histogram is missing. And looking at our imagery, you can see that we have lost some detail. Now the flip side of this is having an under expose image a nd so just for demonstration purposes, I'm going to slide the slider to the left. And here, you can see the information on our histogram sliding to the left leaving a big gap on the right hand side. In this case, clipping is occurring in the shadows of our image. And if you'd like to see specifically where clipping is occurring, you can select this triangle exclamation mark and it'll show you where you're losing detail. And as you can see, we're losing some in her hair as well as the shadows in her jacket and we'll go ahead and deselect that. And the button next to it, the lighter exclamation point shows you clipping that occurs in the highlights. So if we were to go ahead and select that and take the slider back to the right. It shows you where we're losing information in those highlights and we'll go ahead and deselect that exclamation mark and then we're going to reset to default, our exposure compensation slider. In the case of this image, we're going to raise the slider ever so slightly to begin with and you'll notice that the histogram reflects that change. Now let's talk about the highlight compression slider. This allows you to compress the highlights in your image. If you have overexposed areas, it will effectively tone them down. To check if there are any highlights being clipped, once again, you can press the light triangle exclamation mark button above the image and it'll show you that we're losing a little bit of information in the sky here. And so we are going to drag this highlight compression slider ever so slightly to the right to about a value of 22 to recover that information. Beneath that, we have the highlight compression threshold. The highlight compression threshold slider adjusts the point where the above highlight compression slider kicks in. So, the lower you have the slider set, the more the highlights are compressed. And the higher you have it set, the fewer the highlights are compressed and we'll go ahead and leave it at zero. And beneath that, we have the black slider. This is where you'll set your images black point. The black point of an image is the point at which solid black occurs in the most intense shadow areas are clipped to black. In this case, we'll adjust it ever so slightly to a value of about 182, just to increase the black point just a bit. Next, we have the shadow compression slider. This lessens the effect of the black slider above and beneath this, we have the lightness slider, which increases and decreases the lightness of our image. We'll go ahead and leave this slider alone. Beneath that, we have a contrast liner, which increases or decreases our image's contrast. Let's go ahead and increase the contrast of our image ever so slightly, so that it'll looks less washed out. And we'll take it to a value of about 13 for now and so looking at our current step on the right-hand side in our previous step on the left-hand side, you'll see that our image's contrast has ever so slightly been increased and that brings us to the end of this lesson. In this lesson, we discussed the histogram and made some basic correctional adjustments to our image's overall exposure and contrast. In our next lesson, we'll make some baseline color corrections to our photo.

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