Teach you a few tricks Photoshop application skills

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Adobe Photoshop is an excellent image processing software that prepress staff should master. It is very convenient to use. Here are some application tips for some specific examples.

(1) Adjust the hue of the image

Adjust the hue of the image, that is, change the color bias of the image. The commands that can adjust the hue in Photoshop software are color balance, hue/saturation, change, and hue separation.

Color balance

Open the Image/Adjust/Color Balance dialog, where there are three pairs of complementary colors. We know that cyan and blue are cool colors, while red, magenta, and yellow are warm colors, so you only need to adjust the color balance slider to a certain color when adjusting, and the image will become cold or warm. In this dialog box, you can adjust the three levels of the image's dark, middle, and bright colors separately. Check the “Keep Brightness” check box. The brightness of the image is close to the effect, and the change is small. But the level of the image changes a lot.

2. Hue / saturation

To change the red apple to cyan and leave the other colors unchanged, you can use the Image/Adjust/Hid Saturation command. The principle of adjusting the color of the image in this way is to adjust the image from the three properties of the color, namely hue, saturation, and brightness, and can adjust the whole image or a single color.

In the Hue/Saturation window, there are 7 options for full image, red, yellow, green, cyan, blue, and magenta in the “Edit” drop-down menu. Select red and move the mouse to the image to become a pipette tool. Change the color of the area. At this time, a bar will appear on the ribbon below the Hue/Saturation window, indicating the approximate range of the selected color and a certain tolerance. The part between the vertical sliders is “absolutely changing color”. "The vertical slider is a certain "tolerance range" between the triangular sliders on both sides. At the same time, the upper ribbon indicates the image adjustment, and the lower ribbon indicates the image after adjustment. By dragging the indicator and two The slider of the end can change the range of the selected color and its tolerance value. Move the “Hue” slider, the selected color in the image will change, and the saturation and brightness can be adjusted.

Note: If the surrounding ambient color is similar to the selected color, that is, when the hue of the color is adjusted, the surrounding ambient color will also change accordingly. In this case, a rough selection can be made in the constituency. Modify, so the color outside the selection will not change.

But if you want to change the color to a specific color ratio, this method won't work. The double-decker bus color is changed to 80% C, 10% M, 90% Y, and 10% K green, which requires another method.

First, set the matching good color to the foreground color. Open the Layers window and create a new transparent layer, fill the layer with the new foreground color, and select the layer blend mode for Hue from the Mode drop-down list in the Layers window. At this point, the color of the bus will turn green. However, the colors other than the bus will change as the “hue” blending mode changes all non-neutral ash components other than neutral ash. At this point, you can use the Eraser tool, the selection tool, or the mask tool to remove unwanted color changes from the image so that a beautiful green bus is ready. The "change" and "tone separation" commands are simpler and will not be described again.

(2) Smoothing of the gradient

Prepress designer should have this experience, and that is on the computer looks pretty gradient made printed product there is a clear stripe, we can be "noise" process of gradual layers to avoid this problem. Using the Filter/Variety/Add Noise feature, for a 300d pi image, the amount of noise is typically set to 3, and the print is much smoother than before.

(three) adjustment of clarity

Sharpening of printed images is typically done using the "USM" tool, which provides parameter settings that make it the best sharpening option. USM sharpening has three parameter settings: “quantity”, “threshold”, and “radius”. "Quantity" refers to the intensity of the sharpening effect; "Threshold" determines how much contrast adjacent pixel boundaries can be sharpened, and below this contrast will not be sharpened, level 0 settings indicate in the image All tones are sharpened; the "radius" determines the width of the pixel that is edge emphasized. The small setting of the Radius ensures that there is no problem when using higher intensity sharpening.

There should be different clarity requirements and sharpening parameters for different types of images.

Note: If you apply "USM Sharpening" to make the light colors appear too saturated, here are some tips to use. If you want to sharpen the entire image, the color in each channel will be affected. However, the sharpening effect of an image depends largely on the relative brightness of the tone rather than its color information. If the color can be ignored when sharpening, the edges of the image will not be subject to any distortion that may occur, and the sharp edge glow will be eliminated.

In order to do this, the image mode must first be converted to Lab mode. When applying the sharpening filter, it only works on the "brightness" channel, so that it does not affect the color component of the sharpened image. Because the brightness value contains all the brightness and contrast details in the image, the a and b channels contain all the color information, and the L ab mode is the largest color space, so that the color information is not lost when the image is sharpened and then converted. Click on the “Brightness” channel on the channel panel and then apply “USM Sharpen Filter” to achieve better results than other sharpening methods. After sharpening, just convert to RGB or CMYK mode. The reader can try to over-sharp an image in two different modes, RGB and La, and then compare the effects of image edge changes. (Editor: Zhang Wei)

The above content is selected from Keyin Media. Digital Printing, No. 2, 2015, more journal content, please pay attention to the journal channel


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