What Line Pairs Measure
One line pair is one black bar plus one white bar. As the bars get finer, every camera eventually blurs them into flat gray — that point is its resolving limit, set by the lens, the sensor’s pixel count and the camera’s processing together. CamTestKit snaps every bar to whole device pixels, so the pattern itself is perfectly sharp and any blur you see comes from the camera.
How to Use the Resolution Chart
- Go fullscreen with “Snap to device pixels” on.
- Mount the camera square to the screen and focus carefully, using manual focus and magnification if available.
- Fixed mode: raise the line-pair count until the bars merge into gray in the photo. Sweep mode: one photo is enough — find where contrast disappears.
- Enter the line pairs and the pattern’s width in the photo into the calculator.
Important — keep the camera far enough back. The chart can only be as fine as your screen’s pixels. If the screen covers more camera pixels than it has screen pixels, you are measuring the monitor, not the camera. Move back (or zoom out) until the pattern spans fewer pixels in the photo than it does on screen.
Calculating Resolution from Your Photo
- Cycles per pixel = line pairs ÷ pattern width in photo pixels.
- % of Nyquist = cycles per pixel ÷ 0.5. The theoretical maximum for any sensor is 0.5 cycles per pixel (one line pair per two pixels).
- LW/PH (line widths per picture height) = 2 × cycles per pixel × photo height — the unit used in most camera reviews.
Example: bars merge at 150 line pairs while the pattern spans 500 photo pixels → 0.30 cycles/pixel = 60 % of Nyquist; on a 1080-pixel-tall photo that is about 648 LW/PH.
Frequency Sweep Mode
The sweep shrinks the bar period smoothly from 64 to 2 screen pixels across the screen, with tick labels at 32, 16, 8, 6, 4, 3 and 2 px. A single photo shows the whole contrast curve at once: read the tick nearest the point where the bars fade to gray.
Moiré and False Color
Before the bars disappear completely you may see wide wavy bands or rainbow colors. That is aliasing: detail finer than the sensor can sample folding back into coarser false patterns, made colorful by the sensor’s color filter array and demosaicing. Cameras with an optical low-pass filter show less moiré but slightly softer images.
Resolution Chart FAQ
Why should the camera be far from the screen?
The finest bars on screen are 2 screen pixels per line pair. If the camera has more pixels across the pattern than the screen has, it resolves the screen easily and you only learn about the monitor. Moving back makes the camera the limiting factor.
What does Snap to device pixels do?
It rounds the bar width to a whole number of physical screen pixels so every bar has a crisp edge with no anti-aliased gray. Turning it off allows exact line-pair counts at the cost of slightly soft edges.
Is this an MTF test?
It finds the practical limiting resolution, roughly where contrast falls to near zero. A full MTF curve needs a slanted-edge chart and analysis software, but line pairs are a quick, intuitive way to compare cameras and settings.
Why do I see colored patterns before the bars disappear?
That is moiré: detail finer than the sensor can sample creates false patterns, and the color filter array adds false colors. It is a property of the camera, not the chart.