Assuming its an rgb image, you can do rgb2hsv to find the hue and saturation of pixels. Value is similar to brightness, but you may mean brightness from the hsb space. There is no function rgb2hsb.
Also note that saturation is/could be defined differently in other colorspaces. E.g. saturation of a pixel in hsl space is not the same as its saturation in hsv space.
Contrast could be defined as a ratio. E.g. highest brightness / lowest brightness in image.
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