In a histogram, what does the y-axis indicate?

In a histogram related to imaging, the y-axis represents the number of pixels that correspond to each gray value in the image. This means that for each specific gray level on the x-axis, the histogram indicates how many pixels in the image have that particular gray level.

This visualization helps in understanding the distribution of pixel intensities within the image, allowing for assessments of contrast and brightness and facilitating adjustments during post-processing. By analyzing the histogram, clinicians and radiologists can assess the overall exposure of the image and determine if the image is well-exposed, underexposed, or overexposed based on the spread of pixel values. The relationship between pixel counts and gray levels is fundamental for optimizing image quality in diagnostic imaging.

The maximum gray level, total number of x-ray photons detected, and range of brightness levels refer to different aspects of the imaging process but do not represent what is plotted on the y-axis of a histogram. These elements might be important in understanding image quality and exposure, but the specific focus of the y-axis in a histogram is on the pixel count related to gray values.