White and black dust spots on scans?

What causes each? How to tell one from the other? Dust on sheet film before shooting, during scanning, on glass, etc?

Hi Alan, Dust on sheet film before exposure causes black spots in the image after scanning. I tend to get these on my medium format bellows folding camera shots from dirty bellows. Dust on the film or glass during scanning causes white spots if scanning negatives or black spots if scanning transparencies.

hsandler said:

Hi Alan, Dust on sheet film before exposure causes black spots in the image after scanning. I tend to get these on my medium format bellows folding camera shots from dirty bellows. Dust on the film or glass during scanning causes white spots if scanning negatives or black spots if scanning transparencies.

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What kind of film regarding bolded sentence?

Alan Edward Klein said:

What kind of film regarding bolded sentence?

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Any kind. Light doesnt expose the bit of film under the dust speck, so it develops black if it’s transparency film, or clear if it’s negative film, hence causing a black spot when scanned and inverted.