What function in digital image postprocessing enhances image contrast in Digital Subtraction Angiography (DSA)?

In Digital Subtraction Angiography (DSA), the primary function that enhances image contrast is subtraction. This technique involves taking two images: one that captures the anatomy in question without contrast media and another that shows the anatomy after the contrast agent has been administered. By subtracting the first image from the second, the enhanced details of the blood vessels are revealed, while the background anatomy remains relatively suppressed. This process improves the clarity and visibility of the vascular structures, allowing for better assessment and diagnosis.

The other functions, such as compression, filtering, and general enhancement, play roles in image quality and processing but do not specifically engage in the contrast enhancement task that subtraction accomplishes. Compression may reduce file size but doesn't inherently improve contrast, while filtering affects image noise and sharpness without directly enhancing contrast in the way that subtraction does.