Image Processing Steps - Ricoh D009 Service Manual

Image Processing
Pre-Filter Smoothing: Reproduces halftones while reducing the incidence of moiré which
can occur as a result of compressing and then decompressing the image.
Main scan magnification: Adjusts magnification to the desired level by processing
adjusting multiple, adjacent pixels in the direction of main scanning. Adjustment of
magnification in the sub scan direction is done by changing the scanning speed.
Independent dot erase: Attempts to recognize and eliminate scattered, independent dots
in copies. Processes only pixels of high density and eliminates those of low density.
Filtering (MTF filter/smoothing): Performs mainly edge enhancement with the MTF filter.
Performs smoothing only in the Photo mode. The matrix size of the filter is 9 pixels x 7 lines.
Gamma (γ) coefficient: Controls the image density for images processed with grayscaling.
Copy density adjustment is achieved with special notch γ coefficient conversion. The best γ
coefficient suited for the selected mode can be stored and adjusted as needed.
Grayscale processing: Performs reproduction of grayscales, using mainly error diffusion.
(In the Photo mode, conducts processing with dithering.)

6.5.7 IMAGE PROCESSING STEPS

Text Mode
The Text mode achieves quality reproduction of text and sharp lines and ignores
background texture. Processing is conducted with a high resolution MTF filter; special
processing with the γ coefficient prevents background reproduction and achieves the best
reproduction of images with error diffusion. Because the Soft and Normal settings use a
weak MTF filter, the quality of the image is improved with the elimination of moiré. The Sharp
selection uses an MTF filter stronger than that of the Normal setting, thus increasing the
sharpness of lines.
Text/Photo Mode
Text/Photo mode achieves high quality reproduction of pictures with accurate grayscaling.
Processing is conducted with the special γ coefficient which reproduces a wide range of
grayscale. Compared with the Text mode, text reproduced in the Text/Photo mode appears
lighter and textured backgrounds could appear on copies, but the incidence of moiré is
reduced with and edge detection filter. Because Photo Priority uses an MTF filter weaker
than that of the Normal setting, the quality of the image is improved with the elimination of
moiré. The Text Priority selection uses an MTF filter stronger than that of the Normal setting,
thus increasing the sharpness of lines.
Photo Mode
Photo mode emphasizes grayscale processing to achieve the best possible reproduction of
D009/D011/D012/D013 6-20 SM