Performing Thresholding on Color Images

Color Components

Objective

Following this tutorial, you will learn how to use EasyColor to segment a color source image, by setting a threshold value for each color component of the current color system. For example, to retrieve the solder pads on a PCB, you'll perform a color segmentation based on the golden pixels (H), with a loose discrimination on the brightness (L) and saturation (S), to eliminate surface and lighting effects.

You'll need first to load a color source image, create a destination image, and a color lookup table (steps 1-3). Then, you'll set the color system and tune each component tolerance to get a satisfying segmentation of the solder pads (step 4).

Source image

Thresholded image

Step 1: Load the source image

1.

From the main menu, click EasyColor, then Threshold.

2.

Click the Open icon of the Source Image area, and load the image file EasyColor\BGA Substrate Color.jpg.

3.

Keep the default variable name for the new Image object, and click OK.

4.

Disable the Preview Mode check-box to see the raw source image.

Step 2: Create a destination image

1.

Click the New icon of the Destination Image area.

2.

Keep the default variable name for the new Image object, and click OK.

Step 3: Create a color lookup table

1.

Click the New icon of the Color Lookup area.

2.

Keep the default variable name for the new color lookup object, and click OK.

Step 4: Perform the color segmentation

1.

Select LSH from the Color System drop-down list.

2.

In the source image, click in a golden pad. The pixel lightness, saturation and hue values are updated in the Color Threshold dialog box.

3.

Adjust the tolerance of lightness and saturation to enlarge the range of thresholded pixels, until you get a satisfying segmentation in the destination image.