Does scan orientation affect quality on a flatbed all-in-one scanner?
Asked 2/6/2021
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When scanning a photo on the flatbed of an all-in-one printer, it may fit either in portrait or landscape orientation. If the scanner is rated at 600×600 dpi, does placing the photo one way or the other produce better quality, or is the result effectively the same? I'm especially wondering whether the moving scan direction versus the fixed sensor direction makes any academic or practical difference.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
5y ago
2 Answers
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As you've already noticed, there is little practical difference between scans taken at different orientations in most cases.
Scanning images at an angle may help reduce moiré.
Placing items on one side or the other of the sensor will slightly change the perspective of the scan on scanners that use a lens to focus onto a linear sensor. This can be used to scan different images contained in lenticular prints, so the 3D effect can be recreated.
- Your scanner uses a Contact Image Sensor (CIS).
Some scanners can move the scan head in finer increments than the resolution of the sensor. Scanner specs will have different values for x and y. For example, 600x1200. In this case, there is a potential improvement if more of the image is orthogonal to the sensor when scanning at resolutions higher than the sensor resolution.
Most prints do not benefit from scanning at resolutions higher than 200-300 dpi.
Your scanner has a resolution of 600x600.
If there is a defect that affects the sensor or motor, orienting the image orthogonal to the defect may reduce its effect on the image.
- Fixing the defect or using a different scanner would result in much greater improvements.
The scanner motor movement may not exactly match the sensor resolution. The dimensions of scans may be slightly different when the source material is oriented differently.
The difference is usually only a few pixels over the entire document.
A related issue occurs when pages slip on the rollers of form-feed scanners.
Originally by user75526. Source · Licensed CC BY-SA 4.0
user75526
5y ago
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In most real-world use, orientation makes little to no visible difference on a flatbed all-in-one scanner, especially on a CIS-based model like the Samsung C460W.
If the scanner truly samples at the same resolution in both axes (for example 600×600 dpi), scanning the photo in portrait vs. landscape should produce essentially the same detail. Any difference is likely too small to matter in practice.
A difference can exist on some scanners when the optical resolution differs by axis (for example 600×1200 dpi). In that case, orientation could matter slightly at higher resolutions because one direction is sampled more finely than the other. But that does not appear to apply here if the spec is 600×600.
Practically, the biggest difference is scan time: orienting the photo so the scan head travels a shorter distance will finish faster.
Two minor exceptions:
- Scanning at a slight angle can sometimes help reduce moiré on printed material.
- On some lens-based scanners, placement/orientation can slightly affect perspective, but that is not typical for a CIS all-in-one.
So: for your scanner, choose the orientation that is most convenient; quality should be effectively the same.
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