Using Photoshop brings a lot of fun, one of which is the variety of solutions the software offers. As far as adjusting images is concerned, there are many tools to choose from in the Image>Adjustment menu, and Curves is one of the very distinctive tools.
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;
Through the curve, you can adjust the contrast of the entire or individual channels, adjust the brightness of any part, and adjust the color. Although this article does not provide a detailed explanation of the special effects using curves, it may give friends who have read it a new understanding of curves, which will become your right-hand assistant when editing pictures.
Open the Image > Adjustments > Curves command, shortcut Ctrl+M, and the Curves dialog box will appear. If the 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 better observe. 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. To avoid confusion, it is recommended to set it to a mode you are familiar with before adjusting. The standard curve will give you more intuitive understanding.
Since the curve reflects the brightness value of the image, a pixel has a certain brightness value, which can be changed to make it brighter or darker. Observe the following two pictures. The horizontal grayscale bar represents the tone of the original image, and the vertical grayscale bar represents the tone of the adjusted image. 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, image curves change much more gently.)
Application of curves in grayscale images
Below is an image captured on a dim evening that lacks contrast, with pixels too concentrated in the mid-tone range. Through curves, it can be improved.
Original picture and curve display
Increase the brightness of the adjustment point and the overall picture will become brighter.
Reduce the brightness of the adjustment point and the overall picture will become darker.
As can be seen from the above, neither increasing nor decreasing the curve brightness alone can completely solve the problem. They improve one part of the image while destroying another part of the image. 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.
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, which has no highlights or shadows, you can initially reduce the range of the curves to increase the contrast. As mentioned 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. This method is very useful for most mid-tone images that lack contrast! Similarly, adjust the sliders at the ends of the color scale to focus them towards the middle. Granted, in this example, it might be more clear using the Levels tool. Here is a little trick that allows you to quickly create an invert effect: move the black endpoint from the bottom left to the top, and move the white endpoint from the top right to the bottom, so you don’t have to use the invert command. The same effect is achieved. In fact, not every picture has such bright and dark parts, but most of them do. If used wisely, all images will become stylish.
Below, we introduce three tricks to make better use of curves.
Tip 1: Use the eyedropper tool to set the range
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. Of course, this brings convenience to those who need to save time, but abandoning manual adjustments in favor of automated methods rarely yields the best results. This approach is even more dangerous when the middle values of the color image are assumed to be the lightest and darkest values! In many cases you will want to specify the lightest and darkest parts of the image yourself, It is particularly prominent when dealing with special effects pictures. 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 certain color values, double-click the eyedropper to bring up the color dialog box, where you can set precise values.
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.
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. 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.
The example below is what I just said, and the curve is as shown in the figure.
As you accumulate experience, you will slowly be able to see where the pixels of each tone are on the curve. The more you see, the more certain you will be, so you will have an idea of which ones should be brightened and which ones should be darkened. . This rough analysis is necessary before adjusting the curve. Once placed, these adjustment points can still be moved. You will find that when you place and start adjusting these points, the preview window is as intuitive as your canvas. When the position of the adjustment points and the inclination of the curve change under your hands, the image also changes with your wishes. You don't have to limit yourself to one or two points. (Although Photoshop allows you to place up to 16 adjustment points, in general, two points are enough.) The adjustment process will become fast and effective! Of course, the premise of all this is that you must practice more.
Another thing you need to know is that curves cannot be separated from pictures, and there are no universal curves that can be used everywhere. Each picture is unique, so its curves are also unique. The optimal curve shape may vary significantly between images. The center of the image is also different, some are bright (polar bear on the glacier), some are dark (black cat on the coal pile in the basement), and some are mid-tone (like the people in the example above). Now you know how to work with different images: use the mouse to click on the range you want to adjust; mark on the curve; change the slope of the curve to increase contrast. Below are examples.
