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Photoshop CS4's adjustment features offer unparalleled opportunities to correct and manipulate images. In Photoshop CS4: Image Adjustments in Depth, Jan Kabili explains how to use all the major Photoshop adjustment features. She shares the best techniques for adjusting image quality, and shows how to use the new Adjustments panel to streamline a photo correction workflow. Jan also demonstrates multiple ways to eliminate color casts, and explains how to use the new On-Image Curves control to adjust brightness and color. This course offers a detailed look at the techniques photographers and designers use to master image adjustments in Photoshop. Exercise files accompany the course.
This chapter is all about correcting tonal values which are the darks, the lights and the mid-tones that make up the underlying tonal structure of every image whether it's a color photograph like this one or a black and white image. Colors sometimes makes it difficult to see tone but if you squint your eyes that often helps you to envision the underlying gray scale tones that make up an image. I don't have to squint very much in this case to see that this image is dull and flat. It lacks bright whites and dark darks. One way to fix a flat image like this is to increase its contrast and tweak its brightness using a Levels adjustment and that's what I'm going to show you how to do in this movie. I can apply a Levels adjustment as a direct adjustment from the Image menu at the top of the screen.
But as you know, from previous movies I prefer using a nondestructive re-editable adjustment layer whenever I can. So I'm going to apply Levels from over here in the adjustments panel by clicking the Levels icon, which is the second one in the top row. Then I'll go down to my Layers panel and I'll expand that panel by Double-clicking the Layers tab so that you can see that has added a Levels adjustment layer above the background layer that contains the image in this case. I'm going to go back to my Adjustments panel by Double-clicking its tab to show you the controls in the Levels Adjustment panel. The first thing you'll notice here is that the Levels Adjustment panel has a histogram in it and that histogram looks just like the histogram up here in the Histogram panel. So why do I have the Histogram panel open. The reason is that, there's one big difference between these two histograms.
As I modify the Levels here in the Levels Adjustment panel, this histogram will not update. It will always look like it does now. But as I make those adjustments, the histogram in the Histogram panel will automatically update and that will help me to see the effects of the changes that I'm making. So I like to have the Histogram panel open when I'm using Levels. Down in the Adjustments panel the histogram represents the possible tonal values in the open image. The far left side of the histogram represents the darkest possible values and the far right, the brightest possible values.
This mound is actually made up of individual vertical bars, the taller the bar, the higher the relative frequency of the corresponding tonal value and you can see the tonal value of any one of these bars by moving straight down from that bar to this gradient down here. So the very tallest bar in this image represents this kind of middle gray that I can see here in the black to white gradient. I can also see in this histogram that there are no bars at all in the brighter parts of the tonal range and there are only a very few bars here in the darker parts of the tonal range. So my goal in adjusting this image is going to be to create some bright whites and some dark darks in this image and to expand the middle tones in the image across the entire tonal range and that will add contrast to the image so that it hopefully will look a lot less dull than it currently does.
I'm going to start by setting the white point for the image and I'll do that by coming over to this white input slider here, clicking-and-dragging it until it's just beneath some of the vertical bars in the image. The trick here is knowing how far in to go. If I pull this white slider in too far, I'm pushing the tones directly above it and all the tones to the right of it to pure white with no detail or texture and you can see that in the image. This is called clipping the highlights and it's something that you normally want to avoid.
So I'm going to take that white slider and start again by dragging it all the way over to the right and this time I'm going to use a built-in guide called the Threshold view to help me decide where to drop that white slider. To use Threshold view, I hold down the Option key on my keyboard, that's the Alt key on a PC and I'll drag that white slider over to the right. And when I hit that mound of vertical bars I'll start to see some colored pixels in the image that represent clipping in individual Color Channels. I'm going to keep going until I see some white right there in the middle of that colored area. The white pixels represent pixels in the image that will now be clipped to pure white with no detail.
So I just want to have a few of those pixels and then I'll release my mouse. And you can see that I have lightened the bright points of the image but that there is still detail in most of the white areas. Now I'm going to do the same thing with the black slider. I'll click on it while holding down the Option key on a Mac or the Alt key on a PC and I'll drag to the right. In the Threshold view the entire image looks white to start with and as I go to the right I start to see a few black pixels right there on the center of the image. So I'm going to release my mouse and what I have done is actually set the dark area here to pure black.
Now let's see a before and after view by going down to the Eye icon at the bottom of the Adjustment panel and clicking that. This is how the image looked when I started this adjustment and this is the way that it looks now. You can see a diagram of the results up here in the histogram that's in the histogram panel. I now have pixels in the brightest parts of the histogram and in the darkest parts of the histogram and the gray tones in between those two anchor points have now been spread out across the entire histogram. So what I have done is increase the contrast of the image by setting white and black points and letting Levels automatically increase the tonal range of the image.
When you make an adjustment like this, there's one thing to watch out for. Notice in the histogram that there are now some gaps between these vertical bars. Those gaps represent tones for which there are no pixels in the image right now. I don't really see any problem in this particular image but if I was working in an image in which I was going to make extreme tonal changes or repeated tonal changes, gaps in the histogram can cause visible banding or posterization. The solution for that is to start out with as much tonal information as you can in an image. So if you are shooting with a digital camera, consider shooting in raw mode which produces 16-bit files and if you are scanning, try to scan with as high a bit-depth as you can, so that you are starting off in Photoshop with as much tonal information as you can get before you make your adjustments.
I'm going to go back to the Adjustments panel one more time to show you another feature and that is the Output Levels feature down here. Output Levels are used when you are preparing an image for print in order to compensate for the difficulties that printers have in printing very dark darks and very bright brights while retaining detail. Using Output Levels I can remap the very brightest whites to slightly darker tones by taking the white slider here and dragging it over to the left. I'll put it at about 245 and I can do the same for the darkest shadows in the image by taking this black slider and dragging it over to the right.
The exact values that you need to use for Output Levels depend on the printer that you are preparing your image for. So the numbers that I'm showing you here are just within the generally acceptable range of print Output Levels. Another thing to keep in mind when you are increasing contrast with Levels is that sometimes that can introduce a color cast to your image. So if that happens to you, you'll have to add yet another kind of adjustment like a Hue/Saturation adjustment or perhaps a Color Balance adjustment and I'll be addressing those Color adjustments in another chapter.
But for now, just knowing how Levels work can help you take a so-so photograph and change it into one that really pops by setting its black and white points, increasing its tonal range and brightening or darkening the entire image with a Levels adjustment.
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