The Photocopy Canon digital image processing and image memory are controlled by the main controller PCB. The following is a block diagram of digital image processing :
This processing is used as an auxiliary means for adjusting the density of images.
2.2 Input Image Processing
The image data from the reader unit is processed for the following:
2.2.1 Image Data from the Reader Unit
The image signals from the reader unit are 8-bit, 256-gradation intensity image signals which have been subjected to shading correction. The signals arrive from two signal lines (for even- and odd-numbered pixels).
2.2.2 Enlargement/Reduction (main scanning direction)
An image is enlarged or reduced by processing image data when writing it into or reading it from image memory.
2.2.3 Edge Emphasis
For each mode (text, text/photo, print photo, film photo), edge emphasis is executed so as to increase sharpness while suppressing moire.
The machine provides various editing functions: negative/positive reversal, mirror, fold.
2.2.5 Density Conversion (LUT)
In this block, the intensity image signals are converted into density image signals, and processing is executed so as to enable the best output density curve for a specific mode in question.
a. LOG Conversion
Using a LOG conversion table, intensity image signals based on reflected light are converted into density image signals based on density data.
b. Density Adjustment (F-value conversion)
The F-value table most suited to the setting of the Density key in the control panel is used to adjust the density; it, however, will not be executed in memory copy mode.
c. Density Correction (g conversion)
The g conversion table best suited to each specific mode (test, text/photo, print photo, film photo) is used to correct density.
2.2.6 Binary Processing (error diffusion method T-BIC)
In the error diffusion method (T-BIC), the texture is controlled to process the data for optimum printing effects; 8-bit image density signals of each mode (text, text/photo, print photo) are converted into 1-bit image density signals (binary).
2.2.7 Binary (dither screen method)
In the dither screen method, the texture is controlled to process the data for optimum printing effects; 8-bit image density signals for film photo mode are converted into 1-bit image density signals (binary).
Although expressed in binary, the resulting signals enable reproduction in 256 gradations (dither screening of 40×40 pixels).
2.3 Image Memory Control
The image data after binary processing is controlled for the following:
2.3.1 Compression/De-Compression, Rotation, and Enlargement/Reduction
The binary data generated as the result of the foregoing processes is subjected to the following: compression/de-compression (for electronic sorting), rotation, resolution conversion.
The image data subjected to image memory control is temporarily stored in SDRAM.
The HDD functioning as an image server is used to store image data for the Box function.
2.4 Output Image Processing
The output image data to the printer unit is subjected to the following processing:
a. When Generating Read Images In the case of text or test/photo mode, the input image of 600×600 dpi is converted into 1200*×600 dpi by means of smoothing.
In smoothing, image data is compared against a template consisting of several combinations of pattern matrixes for replacement of selected pixels. In addition, notch processing is also executed at the same time as a pattern unique to read image.
b. When Generating Printer (PDL) Images
The image data is subjected to the type of smoothing best suited to PDL, in which 600×600 dpi is converted into 2400*×600 dpi.
2.4.2 Binary-Binary Density Conversion (read image output only)