Authorization statement from the original author. This article is from GURUSNETWORK and published on the goldenmean.com. Steve Nelson, the only author of this tutorial, thanks REALAQU (the only legal Chinese translator) for broadening my tutorial to a wider network space. All related pictures and copyrights belong to NELSON.
I, Realaqu, the only authorized Chinese translator so far, do respect the copyright of Steve Nelson, the author of the following tutorial.
All credits goes to Steve Nelson, the only author of this tutorial.
Any correspondence with Steve Nelson in this tutorial, Please refer to www.thegoldenmean.com The English version of this Tutorial is the only correct version.
The number of images has never been growing as fast as it is now. If you get your images from an experienced photographer or a reputable photo company, you can use them with confidence most of the time. But there are also many times when the pictures you get have poor contrast and severe color casts. For example, they come from poor picture discs, or digital cameras and scanners with poor quality, or many free pictures on the Internet. So when using Previously, it was necessary to modify an image, and sometimes a "good" image needed further processing.
There is a controversial comment: No matter who is engaged in image editing, he must be familiar with curves, and their application is as natural as breathing. This argument is bold enough! Has it caught your attention? If I were forced to give up all but one of my image adjustment tools, it would be Curves! Experts agree that curves are the number one method you can use to improve image quality!
Now, let’s clear up some misconceptions immediately:
Curves are not filters. They make some adjustments to the image on the basis of being faithful to the original image, unlike filters that can create out-of-nowhere effects;
Curves are not that elusive, and with a few basics you can master filters as quickly as you master any other tool;
Controlling the curve can bring you more dramatic works, and more excitement will come from your hands;
Curves will not directly add points to your image, nor can they help you attract the attention of the opposite sex - except your boss!
One of the real pleasures that Photoshop gives you is that the software provides you with many solutions to difficult problems. As far as adjusting images is concerned, in the Image>Adjustment menu, you have many tools to choose from. The reason I like Curves the most is that with this tool alone you can:
Adjust the contrast of the entire or individual channels;
Adjust the brightness of any part;
Adjust the color.
Curves can precisely adjust images, giving new life to pictures that should have been scrapped!
Although this article is biased towards Photoshop, (especially the illustrations), the curve adjustment function is important to everyone who works with images, so even if you don’t use Photoshop, you can get a lot of useful help from it. . There are no special effects using curves in this article, although that certainly falls under the category of special effects. This article is helpful for non-experts who edit images every day to make them look better. Believe me, after reading this article, curves will become your right-hand man, just like a hammer is to a carpenter!
Now, let us unveil the mystery of curves little by little!
Chapter 1: First understanding of the curve
Figure 01
Open the Image>Adjustment>Curve command, shortcut Ctrl+M, and the Curve dialog box will appear. (Figure 01) If necessary, we will explain each detail separately. Now let’s prepare some basic knowledge. If your screen looks different from the picture, hold down Alt and click within the grid to switch between large and small grids. The grid size has no effect on the curve function, but a smaller grid can help you adjust the curve. Good observation. Also note the two small triangles in the middle of the grayscale strip. The default for RGB images is black on the left and white on the right, that is, from the dark area to the bright area of the image, while the default for CMYK images is exactly the opposite. (Fig. 02) To avoid confusion, I recommend that you set it to a mode you are familiar with before making adjustments. The standard curve will give you more intuitive understanding.
Figure 02
First of all, the most obvious fact is - there is no curve change! Why? You know, the curve reflects the brightness value of the image. A pixel has a certain brightness value that you can change to make it brighter or darker. Look at these two pictures (Figure 03, 04). The horizontal grayscale bars below represent the tone of the original image, and the vertical grayscale bars represent the adjusted image tone. Without any changes, the input and output tonal values are equal, so the curve is a straight line at 45 degrees, which is why there is no change in the curve. When you make a change to any point on the curve, you also change the corresponding pixels of the same brightness on the image. Click to establish an adjustment point. This point can be dragged to any range within the grid. Whether it is bright or dark depends on whether you are up or down. A sudden change in the brightness value will create a very eye-catching effect; a slow and gradual change, whether it is increasing or decreasing the brightness value, will make the tone transition smooth and the effect realistic. The following example demonstrates what happens to the image when certain values on the curve are changed, and you can clearly see the shape of the curve changing. (The curves in this example are somewhat exaggerated to show the effect. Sometimes you need strongly varying curves, but most of the time, the curves in the image change much more gently.)
Figure 03
Figure 04
Chapter 2: Application of Curves in Grayscale Images
After a period of explanation, we finally reached the actual operation stage. In this part, we will first process a grayscale image to lay the foundation. Color images will be discussed in the next chapter. Now let's take a look at this poor image (Fig.05): captured with a digital camera on a dim evening, it lacks contrast and the pixels are too concentrated in the mid-tone range. You may also encounter something like this at work. Can we use curves to improve? The answer is yes.
Figure 05
Figure 061-062: Original picture and curve, the adjustment points have not changed;
Figure 061
Figure 062
Figure 071-072: Increase the brightness of the adjustment point and the overall picture will become brighter;
Figure 071
Figure 072
Figure 081-082: Reduce the brightness of the adjustment point and the overall picture will become darker.
Figure 081
Figure 082
You may have discovered that neither raising nor lowering the curve brightness alone completely solves the problem; they improve one part of the image while destroying another. If we can learn from each other's strengths, the problem will be solved. Another feature of curves is that multiple adjustment points can be added. Add adjustment points anywhere in the image and adjust them individually, so that you can adjust areas with different brightness and color values. For this image, two adjustment points work well: increasing the brightness value in the bright areas and decreasing the brightness value in the dark areas. (Figure 091-092)
Figure 091
Figure 092
Tips: Hold down Shift to select multiple adjustment points. If you want to delete a certain point, you can drag the point outside the curve coordinate area, or hold down Ctrl and click the point.
In fact, in an image like this, where there are no highlights or shadows, I would initially narrow down the curves to increase the contrast. As we have said before, any point within the grid can be moved, including of course the two end points of the curve. If we make sure the "curve" is straight and move the dark endpoint of the curve to the right and the light endpoint to the left, the curve becomes steeper, increasing the contrast of the midtones. (Figure 10) This method is very useful for most mid-tone images that lack contrast! Similar to this, adjust the sliders at the ends of the color scale so that they converge towards the middle. Granted, in this example, it might be more clear using the Levels tool. (Using the curve tool does not mean that you cannot use color levels, changes, etc. Here, "any means" to achieve the goal is not a bad thing) Here is a little trick that allows you to quickly create an inversion effect: Move the black endpoint from the bottom on the left to the top, and move the white endpoint from the top on the right to the bottom, so you can achieve the same effect without using the invert command. Now you may be thinking: not every picture has such light and dark areas. That’s right! But most of them are like this. If you take advantage of it, all your images will look stylish!
Figure 10
We have the theoretical foundation, and here are three top-secret weapons that will earn you the respect and admiration of your knowledgeable colleagues. These three tricks are equally useful on grayscale images and color images, but for convenience, we still use grayscale images as an example. Don’t miss it!
Tip 1: Use the eyedropper tool to set the range
Figure 11
Did you notice the part in Figure 11? The preview window allows you to see the changes made and must be opened. Use the "Auto" option with caution, as clicking this button will cause the brightest pixels in the image to turn white and the darkest pixels turn black. (Figure 12) Of course, this will bring convenience to those who need to save time, but abandoning manual adjustments in favor of automatic methods will rarely provide the best results. This approach is even more dangerous when the middle values of the color image are assumed to be the brightest and darkest values! There are many situations where you will want to specify the lightest and darkest parts of an image yourself, this is especially true when working with special effects images. You can do this with the eyedropper tool. Select the black eyedropper on the left and click in the image window where you want it to be black, and the same for white. Since our example image is a grayscale image, the grayscale straw is useless here. Fast and precise! If you are preparing an image for printing and need more specific color values, double-click on the eyedropper to bring up the Color dialog box, where you can set precise values.
Figure 12
Tip 2: Check the brightness value on the curve
This is a cool trick: if you want to know the definite value of any point on the image, you can move the mouse to the image window, the pointer turns into a straw, click on the place you want to view, and this will appear on the curve. A point corresponding to a point. This method is very useful when you need to change the brightness value of a specific place without knowing its position on the curve. Worried about not remembering the exact location? Don’t worry, Photoshop has already thought of this for you. While clicking on the image, hold down the Ctrl key so that the point will be fixed. (Figure 13)
Figure 13
Tip 3: Enhance contrast in specific places
This method is based on the previous method. We will optimize the image, that is, highlight the theme of the picture. Many pictures have a fixed theme, such as people in the environment, etc. Most of the time, we do more with this theme than the background picture. As the saying goes: If there is steel, it must be used on the blade. In the case of limited energy, we should try our best to focus on the most important parts and highlight the center. We have just seen that a steep curve will increase the contrast of the image. Now hold down Ctrl and click around the screen to find the corresponding point on the curve. You can take multiple points, keep the top and bottom ones, and delete the others. Now you know where to work on those parts of the curve. Increasing the slope of the curve will result in more detail. That is, don’t be too bright or too dark, try more and try to balance it with the picture. Sometimes the range taken is a little wider, and that’s not a bad thing, it’s just background. (Figure 14)
Figure 14
The example below is what I just said, and the curve is as shown in the figure. (Figure 151-153)
Figure 151
Figure 152
Figure 153