Method for enhancing image data by sharpening

A process for enhancing a pixel value in an image data defined by a two-dimensional array of pixel values comprising the steps of:

• selecting a first pixel value to be enhanced, X, from the array of pixel values;
• selecting a group of pixel values each identified by p(i), surrounding the first pixel value, X, from the array of pixel values;
• selecting each pixel value p(i) from the group of pixel values to calculate a scaled difference in pixel values between the selected pixel value, p(i), and the first pixel value, X, until scaled difference values have been calculated for substantially all pixel values in the selected group of pixel values, the scaled difference in pixel values being given by a formula (X−p(i)*GAIN, where GAIN is a scaling factor;
• identifying scaled difference values whose magnitudes exceed a threshold value,THRESHOLD;
• and
• deriving an enhanced second pixel value for the first pixel value, X, by adding an average of the identified scaled difference values to the first pixel value, X.

A program storage device readable by a computing device, tangibly embodying a program of instructions, executable by the computing device to perform the method steps for enhancing a pixel value in an image data defined by a two-dimensional array of pixel values, the method comprising the steps of:

• selecting a first pixel value to be enhanced from the array of pixel values;
• selecting a group of pixel values surrounding the first pixel;
• and
• changing the first pixel value to an enhanced second pixel value as a function of differences in values between each of the pixel values in the selected group and the first pixel value, the difference in values are to exceed a threshold value;
• wherein the image data comprises decompressed JPEG image data which contains JPEG compression artifacts and wherein the threshold value is selected to avoid enhancing the JPEG compression artifacts.

A method for sharpeninig a decompressed JPEG color image, comprising:

• decompressing image values which have been previously transformed, divided, discret-cosine-transformed, quantized, and encoded with headers that include quantization tables and coding tables to recover a set of reconstructed pixel values;
• smoothing data obtained in the step of decompressing to reduce pixel-to-pixel discontinuities;
• sharpening in a single pass the data obtained in the step of smoothing;
• halftoning data derived from the step of sharpening;
• and forwarding the data obtained in the step of halftoning for an inkjet print engine.

A method of sharpening image pixels for a printer, comprising:

• receiving a two-dimensional array of pixel values of a smoothing image from a smoothing process that included JPEG compression artifacts;
• processing to sharpen real objects in said two-dimensional array of pixel values while avoiding said JPEG compression artifacts by calculating pixel-by-pixel an enhanced value for a luminance component that is dependent on each of its surrounding pixel values if the particular pixel value exceeds a threshold value;
• amplifying said enhanced value for each said luminance component by an empirically determined gain value;
• and
• halftoning data obtainied in the step of amplifying for use by an inkjet print engine.