US Patent 7738700 Image processing apparatus, control method therefor, and program

The horizontal and vertical projection histograms of an image to be processed are calculated. The autocorrelation values of the calculated horizontal and vertical projection histograms are calculated, and horizontal and vertical object sizes until the autocorrelation values decrease to predetermined thresholds are calculated. The aspect ratio estimate value of the circumscribed rectangle of an object serving as a comparison region candidate in the image to be processed is calculated on the basis of the calculation results. The comparison region candidate is corrected on the basis of the aspect ratio estimate value, determining a final comparison region.