In this paper, we present a novel dichromatic-based method for estimating illuminant chromaticity. The proposed method is essentially based on the Dichromatic Slope and Dichromatic Line Space that we introduce. Dichromatic slope is the slope of the dichromatic line that passes the image chromaticity of a pixel in chromaticity space. It is specularity-invariant and can be computed for each pixel. Accordingly, each pixel can be projected into a three-dimensional dichromatic line space de¯ned in terms of image chromaticity and dichromatic slope. Reliable dichromatic lines can then be obtained by detecting local maxima in dichromatic line space. Illuminant chromaticity is easily estimated by ¯nding the intersections of the resulting dichromatic lines. The proposed method has some advantages. It does not require precise color segmentation, and therefore, can deal with highly textured images. In addition, the proposed method does not su®er from nearly parallel dichromatic lines and it can estimate arti¯cial illuminant chromaticity.