To use the Median filter On a pixel-by-pixel basis, the Median filter applies the median color value of all pixels within the specified radius. Although the filter ignores extreme values in its computations, higher radius values can still wash out an image. 1 Select one or more paint objects to adjust. You can select an area in one image to adjust the selected area only. 2 Choose Image > Filter > Noise > Median. 3 Type a value from 1 to 16 in the Radius text box, or drag the slider. Smaller radius values produce subtler effects. 4 Click OK. To use the Despeckle filter The Despeckle filter can remove defects such as dust and other speckling in images. The filter blends pixels with the lightness values of neighboring pixels. It’s a good idea to select areas that need cor- rection before applying the filter. 1 Select an area in an image to adjust. If you don’t make a selec- tion, the entire image is affected. 2 Choose Image > Filter > Noise > Despeckle. 3 Drag the slider or type a number in the text box to set the Threshold value. Higher values produce greater blending of pixels. To reduce dust and scratch marks The Dust and Scratches filter can remove dust specks by replacing a pixel’s value with a median value. The filter does not change a pixel’s value unless the absolute value of the difference of its gray value and the median gray value of its neighborhood is greater than the Threshold. Larger numbers of pixels are replaced by the median value when the Threshold is low.The practical effect of this is that larger pixels regions (larger “specks”) are reduced or removed with a lower Threshold. Therefore, you can use the Threshold to control the size of the artifacts you want to remove. 1 Select an area to adjust in an image. If you don’t make a selec- tion, the entire object is affected. 2 Choose Image > Filter > Noise > Dust & Scratches.
Canvas 8 Help: Image adjustment and correction (22 of 24)                                           Page #704