Auto Level Histogram will stretch the histogram to the full scale. This works best for pictures - it will improve the whole contrast of the digital image by making sure that the colors are stretched to full scale. Gamma works for midtones. Moving gamma to higher numbers will push midtones towards the lighter color and vice-versa. Excellent for digital images.
Bad image is usually because of the wrong gamma.
Desaturate will simply make the image black and white. Color Boost will make the colors more vibrant by enhancing the in between color contrast. Enhance Photos With UltraSnap you can enhance digital photos in one step. The Photo Filters can make great shot with vivid colors even from bad, flat picture. You have already a Preset Enhanced Photos.