Noisy output when scanning grayscale - Brother DCP-L2500D

[silviucc]

Describe the bug

When scanning using grayscale I get very noisy output

To Reproduce
Steps to reproduce the behavior:

1. Configure scanner to use grayscale mode
2. Scan document

naps2_grayscale.pdf

Expected behavior

It should output a clean scan result

simplescan_grayscale.pdf

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: Ubuntu 24.04
• Version 7.4.2

Additional context
Add any other context about the problem here.

It may be a case where the scanner can do more grayscale scanning modes and simplescan is just selecting the one giving better results by default

[NextTherapist]

What you call a "noisy" output seem to be shades of grey described via error diffusion. Your "clean scan result" is a simple black and white colour reduction.

Somewhere in your scanner driver (probably not in NAPS2) there must be a setting like error diffusion chosen instead of black and white. The setting "Bit depth: Grayscale" is not what you want: you want 1 bit images (black and white).

[silviucc]

Hi.
Below is the output of scanimage. It seems NAPS2 does not show all the modes supported by the driver.

scanimage -A
Output format is not set, using pnm as a default.
scanimage: rounded value of br-x from 211.9 to 211.881
scanimage: rounded value of br-y from 355.6 to 355.567

All options specific to device `brother4:bus7;dev3':
    --mode Black & White|Gray[Error Diffusion]|True Gray|24bit Color[Fast] [24bit Color[Fast]]
        Select the scan mode
    --resolution 100|150|200|300|400|600|1200|2400|4800|9600dpi [200]
        Sets the resolution of the scanned image.
    --source FlatBed [FlatBed]
        Selects the scan source (such as a document-feeder).
    --brightness -50..50% (in steps of 1) [inactive]
        Controls the brightness of the acquired image.
    --contrast -50..50% (in steps of 1) [inactive]
        Controls the contrast of the acquired image.
    -l 0..211.9mm (in steps of 0.0999908) [0]
        Top-left x position of scan area.
    -t 0..355.6mm (in steps of 0.0999908) [0]
        Top-left y position of scan area.
    -x 0..211.9mm (in steps of 0.0999908) [211.881]
        Width of scan-area.
    -y 0..355.6mm (in steps of 0.0999908) [355.567]
        Height of scan-area.

[NextTherapist]

As I said: the setting "Bit depth: Grayscale" is not what you want. What other options are available for "Bit depth"?

[cyanfish]

This should be fixed in 7.5.0.