How to Visualize a Pixel Line Profile from an Image in SciDAVis

A line profile plots the brightness of an image along a straight line: pixel intensity on the y-axis, pixel index along the line on the x-axis. It is the quickest quantitative check in image analysis — measuring the width of a fluorescence band, the edge sharpness of a microscopy image, the intensity gradient across a material sample, or the profile of a spectral line. This guide shows how to draw one in SciDAVis, read the resulting curve, and know where SciDAVis stops and a dedicated image tool takes over.

Prerequisites: your image in a graph window

The line-profile tool works on an image displayed inside a SciDAVis graph window (SciDAVis graphs can embed images as objects on the plot canvas). Open your graph with the image visible at a comfortable zoom — you will be drawing the measurement line by hand, so a large, clear view matters more than anything else.

Step 1 — Right-click the image, choose “View pixel line profile”

Right-click directly on the image in the graph window and select View pixel line profile from the popup menu. A small dialog opens asking for the number of pixels used for the analysis — this sets how densely the line is sampled. Choose a value and click OK.

Step 2 — Draw the measurement line

Click on the image to set the start point of the line, then — keeping the left mouse button pressed — move the cursor to the end point and release. The moment you release the button, SciDAVis opens a new plot window showing pixel intensity versus pixel index along the line you just drew.

• Drawing across a feature (perpendicular to an edge or band) gives a cross-section profile — the classic way to measure widths.
• Drawing along a gradient (parallel to the direction of change) shows how intensity falls off with distance.
• Straight lines only. The tool samples one straight segment; for curved paths, draw several straight profiles and compare them.

Step 3 — Read the profile curve

The result is an ordinary SciDAVis plot window, which means every curve tool you already know applies to it:

• Peak positions and heights read straight off the axes — useful for locating bands or lines in the image.
• Widths: measure the full width at half maximum (FWHM) of a peak with Analysis → Quick Fit and a Gaussian model — the standard way to quote a resolution or feature size. The curve fitting guide walks through the Fit Wizard.
• Comparisons: draw profiles across several regions of the image and plot the resulting curves together (see multi-layer graphs) to show, for example, how an edge degrades from one side of a sample to the other.
• Export the profile curve exactly like any other figure — the export guide covers vector formats for papers.

Practical tips for clean profiles

• Zoom before you draw. A line drawn on a thumbnail lands on different pixels than you think. Zoom the image first, then draw.
• Average over width when possible. A single-pixel-wide line is noisy. Drawing the line slightly wider (or drawing several parallel lines and comparing) shows whether a spike is a real feature or one hot pixel.
• Calibrate the x-axis yourself. SciDAVis reports the x-axis in pixel index — it does not know your pixel size. Convert to micrometers (or arcseconds, or millimeters) manually from your instrument’s calibration and relabel the axis before publishing.
• Save the graph with the line visible. Keep the graph window showing where the line was drawn; six months later you will not remember which transect “Profile3” came from.

When to use SciDAVis vs. a dedicated image tool

The sweet spot is the handoff: extract numbers where the dedicated tool is strongest, then plot, fit, and publish the figures where SciDAVis is strongest.