Abstract: A method and apparatus for a single densitometer design that is used for all colors within multiple color image processing system. The preferred embodiment employs an LED having a light adjustment mechanism for controlling the amount of light received by a light detector in the densitometer. The coarse light adjustment is provided through a variable aperture. Fine light adjustment is accomplished through controlling the current through the LED, either by a potentiometer or through an automated process. Preferably, each of the LEDs is selected by wavelength to maximize the absorption by the colorant yielding light roughly complimentary to the colorant. The adjustment circuit provides advantage in color printing systems by allowing duplicate versions of the same densitometer circuit to yield similar voltage outputs for different colorants, thereby compensating for different absorption characteristics and light output of different colored LEDs.

Abstract: A method and apparatus for preventing voltage swings within device outputs from reading output node where swings in excess of certain voltages can harm electronics attached to the output node. Specifically, output swings from devices performing logarithmic operations are prevented from reaching the input of an A/D converter, thereby protecting the A/D converter from the large swings possible in logarithmic outputs. A comparator circuit compares the output from the logarithmic amplifier against a threshold and engages the switching mechanism once the threshold is reached. Once the switching mechanism is engaged it applies a predetermined voltage to the output node in place of the true output voltage from the logarithmic amplifier.

Abstract: A method and apparatus for a single densitometer design that is used for all colors within multiple color image processing system. The preferred embodiment employs an LED having a light adjustment mechanism for controlling the amount of light received by a light detector in the densitometer. The coarse light adjustment is provided through a variable aperture. Fine light adjustment is accomplished through controlling the current through the LED, either by a potentiometer or through an automated process. Preferably, each of the LEDs is selected by wavelength to maximize the absorption by the colorant yielding light roughly complimentary to the colorant. The adjustment circuit provides advantage in color printing systems by allowing duplicate versions of the same densitometer circuit to yield similar voltage outputs for different colorants, thereby compensating for different absorption characteristics and light output of different colored LEDs.

Abstract: Apparatus for feeding sheets seriatim from a stack of sheets which substantially prevents image ruboff. Such sheet feed apparatus includes a tray for supporting a stack of sheets. A plate associated with the tray supports the lead edge of the sheet stack. A major portion of the sheet stack, measured from the top of the sheet stack at the lead edge of the sheet stack, is supported by a mechanism associated with the plate. A positive flow of air is directed at a minor portion of the sheet stack, measured from the bottom of the sheet stack at the lead edge of the sheet stack, to enable the minor portion of the sheet stack to be levitated for separation of the sheets in the minor portion of the sheet stack.