Does image size affect acutance measurements when comparing cameras?
Asked 6/2/2026
2 views
2 answers
0
I measured acutance from Siemens star images taken with four different devices, but the images are not the same size. Will differing image magnification or output size affect the acutance calculation? I noticed the current ranking matches visual sharpness, but I want to know whether the results are only valid for those specific outputs or whether I need to normalize image size first when comparing the devices.
Originally by Landon Ham. Source · Licensed CC BY-SA 4.0
Landon Ham
9d ago
2 Answers
1
If you are comparing the acutance of the results for different outputs/compositions, then the calculations are correct. I.e. a human needs less contrast in a larger detail in order to perceive it as equally sharp as a smaller detail of higher contrast.
However, if you are comparing the cameras for the same output (composition, print/display size, etc); then you need to normalize for size first.
The correlation to this is measuring MTF in lines/mm (lines/PH, etc)for different lenses. In order for the test chart to have the same lines/mm on the sensor as indicated on the chart, the differences in magnification need to be compensated for. I.e. the chart must be at a greater distance for a longer lens because otherwise it would record/present larger (MTF artificially increased). MTF is also largely a measure of contrast (acutance).
Originally by Steven Kersting. Source · Licensed CC BY-SA 4.0
Steven Kersting
9d ago
0
Generated from our catalog & community — verify before relying on it.
Yes—image size can affect acutance comparisons.
If you are comparing the final outputs as viewed or displayed, then the calculations can be valid as-is: a larger reproduced detail can appear equally sharp even with lower contrast, so acutance can track what the eye sees.
But if your goal is to compare the cameras themselves under the same viewing or output conditions, you should normalize for size first. Different magnification can make one image appear sharper simply because the recorded detail is larger, not because the camera or lens is actually resolving better.
This is similar to MTF testing: magnification must be controlled so the test pattern is recorded at the same scale, otherwise the result is biased.
So the short version is:
- comparing final images at their current sizes: your acutance ranking may be meaningful
- comparing device sharpness fairly: match composition/output size or otherwise normalize scale before calculating acutance
Recommended products
UniqueBot
AI9d ago
Your Answer
Related Questions
How can I quantitatively compare two cameras' color accuracy with a Macbeth ColorChecker if their exposures differ?
How do different light modifiers actually change the look of a portrait?
If I downsample both to 12MP, will a Nikon D3200 have better image quality than a D3100?
Why is an image file often smaller than pixels × bit depth suggests?
Do quoted camera field-of-view specs include lens distortion?