Measuring, Counting, and Analyzing Pixels in Photoshop CC

By Peter Bauer

Designed for researchers and scientists, the measuring capabilities in Photoshop CC are quite powerful. You can measure just about anything and count the number of whatevers in a technical image, perhaps from a microscope or telescope.

Measuring length, area, and more

If you know the exact size of any element in an image, you can then discover just about anything you want to know about anything else in that image. The key is to set the measurement scale, as shown. The Measurement Scale dialog box opens through the Image →Analysis menu or the Measurement Log’s panel menu with the command Set Measurement Scale → Custom.

photoshop-drag
Drag a known distance; set the measurement scale.

In this example, we know that the knee is 2.5 inches wide and that the Ruler tool (nested in the Toolbox with the Eyedropper) was Shift+dragged over 138 pixels. You can, therefore, set the scale to 138 pixels = 2.5 inches. You can add the measurement scale to the image as an editable layer group (visible in the top center) with the Image →Analysis → Place Scale Marker command.

Using any selection tool, you can isolate any part of the image, click the Record Measurements button in the Measurement Log panel (which you open, like any panel, through the Window menu), and you’ll find out more than you ever wanted to know about that particular selection and its content. In addition to the fields visible in the figure, the Measurement Log can also track (among other things) the height, width, area, and perimeter length of the selection, as well as the minimum, maximum, mean, and median gray values within the selection.

After you have made and recorded all the various measurements you need, you can select all the lines in the Measurement Log (or only a few) and click the third button in the upper-right corner of the panel to export the data for use in a spreadsheet program.

Calculating with Vanishing Point

Photoshop also offers measurement in perspective through Vanishing Point (found in the Filter menu). Suppose, for example, you need to calculate how much wallpaper to order for the room shown here. You know the height of the window (70 inches) and using that as your known measurement, you can have Photoshop calculate the height and length of each wall. Drag the Measure tool along the edge of the window and enter the known size (70 inches) in the Length field. When you click the four corners of a surface in the image with the Create Plane tool, the length of each side is visible in boxes.

photoshop-vanishing
Measurements can also be made in perspective with Vanishing Point.

Counting crows or maybe avian flu

Nested with the Ruler tool and the Eyedroppers in the Toolbox is the Count tool. Zoom in and start clicking whatever you need to count, whether they’re birds in the sky or viruses on a slide. Each item you click is labeled with a number. When you want to record the count, click the Record Measurements button in the Measurement Log. You can also record and work with multiple counts. To the right of the Count Groups menu on the Options bar are buttons to show/hide the currently selected count group, to start a new count group, and to delete the current count group. Click the color swatch on the Options bar to select a new color for the count group, and you can customize both the size of the circle that marks the count and the marker number — individually for each count group.

photoshop-tally
Click each item and Photoshop keeps a running tally for you.

(Don’t you love the way that Warning symbol in the margin catches your eye?) Adjust the marker and label sizes (and select a color) before you start clicking around in your image with the Count tool — changing the size after placing your count markers can shift them in the image window, destroying your meticulous placement.