Image processing method to reduce marking material coverage in printing processes

A method for processing a color image for printing by an ink jet printer to reduce ink used thereby, the color image comprised of multiple separations, comprising at least one non-black color separation and a black color separation, each defined by a bitmap of single bit pixels each having a pixel value and arranged in an array of scan lines, comprising the steps of:

• for each separation bitmap, measuring an ink coverage value over a given area within the image and summing the ink coverage of each bitmap to determine total ink coverage;
• comparing desired ink coverage with measured total ink coverage to derive an ON/OFF ratio, where the ON/OFF ratio represents a number of pixels to be turned OFF, compared to the number of pixels ON in a separation;
• setting a number of pixels to OFF in the non-black color separation bitmaps in a larger number of pixels in a separation, in accordance with the turn OFF ratio;
• retaining an ON/OFF state of all of the pixels in the black color separation irrespective of the ON/OFF ratio;
• and
• outputting the separation bitmaps to a print controller.

A method for processing a color image for printing, to reduce an amount of marking material used thereby, the color image comprised of multiple separations, comprising at least one non-black color separation and a black color separation, each defined by a bitmap of single bit pixels each having a pixel value and arranged in an array of scan lines, comprising the steps of:

• receiving pixel values of a set of k pixels from a single scan line of pixels, where k is an integer number of pixels;
• providing a pre-loaded look up table, having a set of k bit addresses, each address corresponding to data entries including a possible combination of marking material coverage values for a set of k pixels;
• storing to a memory, the marking material coverage value from the look up table corresponding to each set of k pixel values for a set of 1 scan lines;
• summing the marking material coverage values for the set of 1 scan lines to derive a marking material coverage value for the area of k pixels by 1 scan lines in each separation;
• summing the marking material coverage values for the separations to derive a marking material coverage value for the image over an area of k pixels by 1 scan lines;
• determining the location in the image of pixels in the non-black color separations that should be turned OFF in accordance with a turn OFF ratio, while retaining unchanged an ON/OFF state of all pixels in the black color separation;
• incrementing a counter value by a predetermined amount related to the turn OFF ratio, whereby increasing the counter value increases the likelihood of the pixel being set OFF;
• comparing the counter value with a reference to determine whether to set the pixel OFF, said comparing generating an ON/OFF determination signal;
• upon determining that a pixel should be turned OFF, resetting the counter so that the next pixel has a decreased probability of being turned OFF;
• performing a masking process between the pixel value and the ON/OFF determination signal to generate a separation bitmap;
• and
• outputting each separation bitmap to a printer.

A device for processing a color image comprised of multiple separations, comprising at least one non-black color separation and a black color separation, each defined by a bitmap of single bit pixels for printing, to reduce an amount of marking material used in the color image, comprising:

• means for predicting the marking material coverage of an area in an output image as a function of the input image;
• means for determining a ratio of pixels to be turned OFF in the non-black color separations, while retaining unchanged an ON/OFF state of all pixels in the black color separation, as a function of a desired marking material coverage for a page on which the color image is printed and the predicted marking material coverage;
• processing order control means, for determining a sequence of pixels processed in the input image for reducing marking material coverage;
• turn off determining means for determining whether a pixel should be turned OFF in the non-black color separations in accordance with the turn OFF ratio, where each pixel is processed in an order controlled by the process order control means, wherein said turn off determining means does not operate on said black color separation;
• a masking circuit, having as inputs the pixels in each separation of the color image and the turn off ratio determination from said turn off determining means, and having as an output a pixel value for a reduced marking material image;
• and
• output means for directing the pixel value to a print controller.