3. März 2009

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Comparative Test Color Lasers up to 700 Euros: Yellow Dots: The secret code

Secret code: Most color lasers print it on every page with color on it.

Identifying the printer: If you take a very close look at a color laser print, you might find very tiny yellow dots. With a magnifying glass, a microscope, or a scanner you can see them better.

More on that you find in this article Code bei Farblasern entschlüsselt, which is available in German only at this time.

The yellow dots are arranged in such a way, that information like manufacturer, serial number of the printer, and the date the sheet was printed can be deduced.

DC makes these infos visible using a simple filter trick. Brother, HP, and Kyocera print this code on every colored page, Oki and Samsung do not.

How to make the yellow dots visible

• 1. Print a page with colored elements, for example one of our templates
• 2. Print a page and scan a small section of it with 600 dpi
• 3. Invert the resulting picture
• 4. Highlight the yellow dots by using a channel mixer
• 5. Play with brightness and contrast to bring out the yellow dots even more clearly

Step 1: Scan a small section with 600 dpi.

Step 2: Invert the picture, using graphical software.

Step 3: Highlight the yellow dots with the channel mixer.

Step 4: Use brightness contrast to enhance the result.

Brother HL-4040CN: With yellow dots.

HP Color Laserjet CP2025n: With yellow dots.

Kyocera FS-C5100DN: With yellow dots.

Oki C3600n: No yellow dots.

Samsung CLP-610ND: No yellow dots.