Blur
The Blur tool 
reduces image sharpness by decreasing color contrast between neighboring pixels.
The basic tool settings are shown in the Tool Options panel above the Image Window or by right-clicking on the image. To display the full list of parameters, press the tool icon in the Tool Options panel or use the F5 key. To specify the parameter settings, enter a numerical value in the parameter’s field or use the slider.
Element - in the drop-down list, select the type of the basic element of the brush: Ellipse or Select Shape.
Size (1-500). Blur brush size (in pixels).
Hardness (0-100). The width of the tool’s outer edge, where the image is partially blurred. The higher the value, the larger the area within the brush where blur is applied completely.
Hardness = 40
Hardness = 90
Radius (0.1-5.0). Intensity of the effect on an image. This parameter specifies the area where points are searched for blurring: at higher values the blurring radius is larger.
Radius = 1.0
Radius = 4.0
Fill (1-100). The amount of blur in a single brush stroke. If you hold the mouse button while drawing, the strokes are overlapped and the blur effect increases.
Fill = 25
Fill = 75
In addition to the above-mentioned parameters, you can adjust the advanced settings that affect the shape and position of the brush marks.
Press the Default button to set all settings to their default values.
To draw a straight line, first specify the starting point with the left mouse button, then, while keeping Shift pressed, move the cursor to the desired end point of the line and release Shift. If Shift is not released, a new line will be drawn to each point where the mouse is clicked.
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