This patent specification describes a barcode-reading system for a mobile device. The mobile device include an image sensor array for generating a color image of a target area. The color image includes sub-images each captured with a portion of the image sensor array sensitive to different bands of illumination. The barcode reading system may include an optic system configured to produce a targeting illumination pattern of a particular band of illumination passed by an optical filter within the target area. An image processing function of a barcode-reading application may create a grayscale composite image of a barcode by combining the sub-images. In combining the sub-images, a contribution from a sub-image captured by a portion of the image sensor array most sensitive to the particular band for the targeting illumination may be smaller than a contribution from the other two sub-images captured by other portions of the image sensor array.