Linear contrast stretching uniformly expands the intensity values in an image to utilize the full range of available intensities. Histogram equalization spreads out intensity values to improve contrast by effectively stretching the most frequent values. Piecewise linear stretching uses different linear functions to enhance different intensity ranges differently. Logarithmic stretching compresses higher intensity values while expanding lower ones, enhancing dark areas. Contrast stretching techniques aim to improve poor contrast by modifying intensity distributions, but can increase noise and lose original brightness levels.