Comparison of image subtractions using the cross‐convolution method described in this paper and the single convolution method described by Alard and Lupton and implemented in the ISIS code. The initial images were obtained by the ROTSE‐IIIb telescope at McDonald Observatory. Shown here are ﹩260\times 260﹩ pixel subframes centered on ﹩\alpha =16^{\mathrm{h}\,}50^{\mathrm{m}\,}02.21^{\mathrm{s}\,}﹩, ﹩\delta =+23^{\circ }46^{\prime }32.88^{\prime \prime }﹩, covering a field of ﹩0.235^{\circ }\times 0.235^{\circ }﹩. To demonstrate the results, three artificial "variable" stars were added to the test image (a) and the reference image (b) with PSFs appropriately matched to their respective fields. The locations are shown by black arrows. The subtracted image obtained by cross‐convolution is depicted in (c), and the Alard‐Lupton results are shown in (d). The bright star near the lower right corner of the images has been replaced with a uniform gray level, since neither subtraction technique can extract useful information from saturated pixels.