Text and image sharpening of JPEG compressed images in the frequency domain

A method of compressing and transmitting images which produces decompressed images having improved text and image quality, the method comprising:

• compressing a source image into compressed image data using a first quantization table (Q.sub.E);
• forming a second quantization table (Q.sub.D), wherein the second quantization table is related to the first quantization table in accordance with a predetermined function of the energy in a reference image and the energy in a scanned image, such that the second quantization table (Q.sub.D) is configured to compensate for image degradation caused by a scanner;
• transmitting the compressed image data;
• and
• decompressing the compressed image data using the second quantization table Q.sub.D.

A method of compressing and transmitting images which produces decompressed images having improved text and image quality, the method comprising:

• compressing a source image into compressed image data using a first quantization table (Q.sub.E);
• forming a second quantization table (Q.sub.D), wherein the second quantization table is related to the first quantization table in accordance with a predetermined function of the energy in a reference image and the energy in a scanned image;
• transmitting the compressed image data;
• and
• decompressing the compressed image data using the second quantization table Q.sub.D ;
• wherein the step of forming a second quantization table includes scaling the first quantization table in accordance with the predetermined function prior to the transmitting step.

A method of compressing and transmitting images which produces decompressed images having improved text and image quality, the method comprising:

• compressing a source image into compressed image data using a first quantization table (Q.sub.E);
• forming a second quantization table (Q.sub.D), wherein the second quantization table is related to the first quantization table in accordance with a predetermined function of the energy in a reference image and the energy in a scanned image;
• transmitting the compressed image data;
• decompressing the compressed image data using the second quantization table Q.sub.D ;
• encapsulating the second quantization table Q.sub.D with the compressed image data to form an encapsulated data file;
• and
• transmitting the encapsulated data file.

A method of forming a quantization table for use in compressing images in accordance with the JPEG compression standard, the method comprising:

• selecting a first quantization table (Q.sub.E);
• and
• forming a second quantization table (Q.sub.D), where the second quantization table is related to the first quantization table according to the following expression:
• Q.sub.D =S.times.Q.sub.E,
• where S is a scaling matrix having each element S›k,l! formed according to the following expression:
• S›k,l!.sup.2 =V*›k,l!/V.sub.Y ›k,l!,
• where V* is a variance matrix of a reference image and V.sub.Y is a variance matrix of a scanned image.

A method of improving text and image quality of compressed images that are compressed using the JPEG compression standard, the method comprising:

• selecting a reference image;
• determining the energy content of the reference image;
• selecting a scanned image;
• determining the energy content of the scanned image;
• selecting a first quantization table (Q.sub.E);
• scaling the first quantization table (Q.sub.E) to form a second quantization table (Q.sub.D) according to the ratio of the energy in the reference image to the energy content of the scanned image, such that the second quantization table (Q.sub.D) is configured to compensate for image degradation caused by a scanner;
• compressing a source image in accordance with the JPEG standard using the first quantization table (Q.sub.E);
• and
• decompressing the source image in accordance with the JPEG standard using the second quantization table Q.sub.D whereby the decompressed image has improved image quality.

A method of improving text and image quality of compressed images that are compressed using the JPEG compression standard, the method comprising:

• selecting a reference image;
• determining the energy content of the reference image;
• selecting a scanned image;
• determining the energy content of the scanned image;
• selecting a first quantization table (Q.sub.E);
• scaling the first quantization table (Q.sub.E) to form a second quantization table (Q.sub.D) according to the ratio of the energy in the reference image to the energy content of the scanned image;
• compressing a source image in accordance with the JPEG standard using the first quantization table (Q.sub.E);
• decompressing the source image in accordance with the JPEG standard using the second quantization table Q.sub.D whereby the decompressed image has improved image quality;
• encapsulating the second quantization table (Q.sub.D) with the compressed image to form a JPEG file;
• and
• transmitting the JPEG file over a limited bandwidth channel.