Reduction during scanning

Theoretically, you should get the same quality scan, no matter whether you scan a certificate full scale at 150 ppi or reduce it 50% during scanning and save it at 300 ppi. The math says:.

150 ppi x 1 inch wide x 100% = 150 pixels across
vs
300 ppi x 1 inche wide x 50% = 150 pixels across

But, the truth is, you can NOT achieve the same quality. Not even close/

I have found that it is always better to scan full scale and then reduce afterwards. I advise to never depend on your scanning software for image reductions. Here are examples comparing the two approaches.

The image on the left was scanned at 150 ppi with no reduction. The image on the right was scanned at 300 ppi with 50% reduction.

Why is that?

Sadly, I don't know for sure. I suspect unpublished assumptions built in the software might explain the image deterioration. I have encountered the same results, no matter whether it was a $150 scanner with entry-level software or a $1000 professional scanner.

My advice?

Scan certificates at full scale and reduce later.

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