Canon CLC5151 Reference Manual page 253

If you want to specify print settings for the sample print:
Press [Sample Print Settings]
You can set the background pattern, the text size, color, and orientation.
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Refer to the sample print and set the contrast value indicated for an
image where the hidden text is difficult to see using [ ] or [ ].
If there is no image where the text is difficult to see:
Press [Standard Value Settings]
Refer to the standard value sample print and set the standard value indicated for the image
which has the most even contrast for the inner and outer squares.
Press [OK] return to step 2.
If you want to adjust the density of the text:
Press [Latent String Density]
Press [OK] return to step 2.
specify the desired settings
[Sample Print] [Yes].
adjust the density using [-] or [+].
Adjusting the Machine
press [OK].
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