với họ ở độ phân giải cao nhất và sau đó thay đổi kích thước chúng nhỏ hơn. Làm việc tại cao hơn của hai hay nhiều nghị quyết giữ lại các chi tiết cho các bài thuyết trình có độ phân giải cao hơn và decimates chi tiết đó sẽ không được | un sharpening and boosting contrast 119 Generally you will want to choose a setting with a low threshold which is measured in levels. This means Photoshop Elements will look at the number of levels of difference in the surrounding pixels and if the number of levels is greater than the threshold it will apply sharpening based on the settings for Radius and Amount. The name Unsharp Mask comes from the traditional darkroom process in which an inverted blurred unsharp duplicate of the original image was sandwiched to mask the exposure during printing. This helped target and adjust sharpen contrast differences. You should usually keep the Threshold setting between 0 and 5 levels toward the lower end of this range. In fact you will often want to use zero tolerance. Low tolerance levels 1 or 2 can keep Photoshop Elements from sharpening what is otherwise image noise. Sharpening noise will only make the image noisier. With that in mind a good rule of thumb is to raise the threshold more for images with more image noise. This will keep you from enhancing image noise. The only time you will set the threshold higher than 5 is when you want to limit the filter s effect to high-contrast areas of the image to play up existing contrast and separation of image elements. Radius and Amount might be set quite differently depending on what you are trying to achieve and the ppi and content of the image. In many cases you might apply the filter twice once with a low radius for general sharpening and once with a higher radius for broader enhancement of image contrast. The following sections cover these techniques. Affecting Sharpness with the Unsharp Mask Filter Sharpening an image with the Unsharp Mask filter depends on Elements recognizing and enhancing existing edges in an image. In other words if the image is too soft or blurry to have defined edges the filter can t tell where the edge is so it can t tell what to enhance. This is why the filter works best to sharpen images that are
