In a recent study, a light sheet imaging approach has been proposed (Hartung et al., J. Appl. Phys. B 96 (2009) 843-862) which permits measurement of a quantity S*D-2(d), which is the two-dimensional projection of the actual density-weighted displacement speed S*(d) for turbulent premixed flames. Here the statistics of S*(d) and S*(2D)(d) are compared using a direct numerical simulation database of statistically planar turbulent premixed flames. It is found that the probability density functions (pdfs) of S*(2D)(d) approximate the pdfs of S*(d) satisfactorily for small values of root-mean-square turbulent velocity fluctuation u', though the S*(2D)(d) pdfs are wider than the S*(d) pdfs. Although the agreement between the pdfs and the standard-deviations of S*(2D)(d) and s*(d) deteriorate with increasing u', the mean values of S*(2D)(d) correspond closely with the mean values of S*(d) for all cases considered here. The pdfs of two-dimensional curvature K-m(2D) and the two-dimensional tangential-diffusion component of density-weighted displacement speed S*(2D)(t) are found to be narrower than their three-dimensional counterparts (i.e. K-m and S*(t) respectively). It has been found that the pdfs, mean and standard-deviation of pi/2 x K-m(2D) pi/2 X S*(2D)(t) faithfully capture the pdfs, mean and standard-deviation of the corresponding three-dimensional counterparts, K-m and S*(t) respectively. The combination of wider S*(2D)(d) pdfs in comparison to S*d pdfs, and narrower S*(2D)(t) pdfs in comparison to S*(t) pdfs, leads to wider (S*(r) + S*(n))(2D) = s*(2D)(d) - S*(2D)(t) pdfs than the pdfs of combined reaction and normal-diffusion components of density-weighted displacement speed (S*(r) + S*(n)). This is reflected in the higher value of standard-deviation of (S*(r) + S*(n))(2D), than that of its three-dimensional counterpart (S*(r) + S*(n)). However, the mean values of (S*(r) + S*(n))(2D) remain close to the mean values of (S*(r) + S*(n)). The loss of perfect correlation between two and three-dimensional quantities leads to important qualitative differences between the (S*(r) + S*(n))(2D) - K-m(2D) and (S*(r) + *(n)) - K-m, and between the S*(2D)(d) - K-m(2D) and S*(d) - K-m correlations. For unity Lewis number flames, the S*(d) - K-m correlation remains strongly negative, whereas a weak correlation is observed between S*(2D)(d) and K-m(2D). The study demonstrates the strengths and limitations of the predictive capabilities of the planar imaging techniques in the context of the measurement of density-weighted displacement speed, which are important for detailed model development or validation based on experimental data. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.