Image quality control in an imaging system

1 . A method of controlling image quality in a digital image printing system, comprising:

acquiring a digital image including a set of pixels, each of which has a pixel value;

printing said digital image on media to produce a digital image print;

measuring the density of at least a subset of said set of pixels on said digital image print to produce a measured density image;

calculating for said subset of said set of pixels of said digital image a predicted density image;

comparing said measured density image and said predicted density image to produce density corrections, if any; and

using any said density corrections to modify software used in printing subsequent digital images to improve the image quality thereof.

2 . A method of controlling image quality in a medical image printing system, comprising:

acquiring a digital medical image including a set of pixels, each of which has a pixel value;

printing said medical image on media to produce a medical image print;

measuring the density of at least said set of pixels on said medical image print to produce a measured density image;

calculating for at least said set of pixels of said digital medical image a predicted density image;

comparing said measured density image and said predicted density image to produce density corrections, if any; and

using any said density corrections to modify software used in printing subsequent digital medical images to improve the image quality thereof.

3 . The method of claim 2 wherein said digital medical image is acquired from one of the following medical image sources, among others, a medical film digitizer, a diagnostic imaging modality, a computed radiography system, a direct digital radiography system, an archive of digital medical images.

4 . The method of claim 2 wherein said printing is carried out by means of one of a medical laser printer which produces medical image prints on thermally processable photothermographic media, an electrophotographic printer, an ink jet printer, a direct thermal printer, a thermal dye transfer printer.

5 . The method of claim 3 wherein said acquired digital medical image is digitally processed by means of a media model lookup table which converts said set of pixels into calibrated exposure values which are used by said medical laser printer to produce said medical image print.

6 . The method of claim 2 wherein said density measuring is carried out by one of a spot densitometer, a 1-D line receptor, and a 2-D area receptor.

7 . The method of claim 2 wherein said density measuring is carried out by means of a spot densitometer having a measuring aperture of predetermined size, wherein said acquired digital medical image includes an array of pixels each of which has a pixel value, and wherein said calculating includes:

using a provided lookup table for mapping pixel value to theoretical printed densities; calculating from the acquired digital medical image, an image of theoretical transmittance values at full printer resolution; calculating, by summing transmittances in small neighborhoods, a reduced resolution transmittance image, which is smaller than the predetermined size of said densitometer aperture; convolving the reduced resolution transmittance image with an aperture mask equivalent to the densitometer's aperture; and

converting the convolved transmittances to optical densities to produce said predicted density image.

8 . The method of claim 2 wherein said comparing includes: using an edge detection algorithm, finding the indices corresponding to media edges in said measured density image;

using known media border thicknesses adjusting the edge indices of said measured density image to correspond to image edges in said measured density image;

for a range of hypothetical small translational offsets and skew, calculating an associated densitometer trace line array, consisting of values extracted from the predicted density image along each hypothetical line;

selecting the hypothetical trace line which gives the greatest consistency along the trace line;

sorting all density differences, between said measured density image and said predicted density image along the chosen trace line, into density bins, and, for bins with a sufficient number of counts, taking the average density difference in that bin as an error estimate of the difference between measured and predicted density, in that density interval; and

modifying the media printing software as a function of this array of density errors to control the image quality of subsequent medical image prints.

9 . A system for controlling image quality in a digital image printing system, comprising:

a digital image printer for printing an acquired digital image including a set of pixels, each of which has a pixel value, on media to produce a medical image print;

a device for measuring the density of at least a subset of said set of pixels on said digital image print to produce a measured density image; and

an image processor and printer control,

which calculates for at least said subset of said set of pixels of said acquired digital image a predicted density image;

which compares said measured density image and said predicted density image to produce density corrections, if any; and

which uses any said density corrections to modify software used in printing subsequent digital images to improve the image quality thereof.

10 . A system for controlling image quality in a medical image printing system, comprising:

a medical image printer for printing an acquired digital medical image including a set of pixels, each of which has a pixel value on media to produce a medical image print;

a device for measuring the density of at least said set of pixels on said medical image print to produce a measured density image; and

an image processor and printer control,

which calculates for at least said set of pixels of said acquired digital medical image a predicted density image;

which compares said measured density image and said predicted density image to produce density corrections, if any; and

which uses any said density corrections to modify software used in printing subsequent digital medical images to improve the image quality thereof.

11 . The system of claim 10 wherein said digital medical image is acquired from one of the following medical image sources, among others, a medical film digitizer, a diagnostic imaging modality, a computed radiography system, a direct digital radiography system, an archive of digital medical images.

12 . The system of claim 10 wherein said medical image printer is one of a medical laser printer which produces medical image prints on thermally processable photothermographic media, an electrophotographic printer, a direct thermal printer, an inkjet printer, a thermal dye transfer printer.

13 . The system of claim 12 wherein said image processor and printer control processes said acquired digital medical image by means of a media model lookup table which converts said set of pixels into calibrated exposure values which are used by said medical laser printer to produce said medical image print.

14 . The system of claim 10 wherein said density measuring device is one of a spot densitometer, a 1-D line receptor, and a 2-D area receptor.

15 . The system of claim 10 wherein said density measuring device is a spot densitometer having a measuring aperture of predetermined size, wherein said acquired digital medical image includes an array of pixels each of which has a pixel value, and wherein said calculating of said image processor and printer control includes:

using a provided lookup table for mapping pixel value to theoretical printed densities;

calculating from the acquired digital medical image, an image of theoretical transmittance values at full printer resolution;

calculating by summing transmittances in small neighborhoods a reduced resolution transmittance image, which is smaller than the predetermined size of said densitometer aperture;

convolving the reduced resolution transmittance image with an aperture mask equivalent to the densitometer's aperture; and converting the convolved transmittances to optical densities to produce said predicted density image.

16 . The system of claim 10 wherein said comparing of said image processor and printer control includes:

using an edge detection algorithm, finding the indices corresponding to media edges in said measured density image;

using known media border thicknesses adjusting the edge indices of said measured density image to correspond to image edges in said measured density image;

for a range of hypothetical small translational offsets and skew, calculating an associated densitometer trace line array, consisting of values extracted from the predicted density image along each hypothetical line;

selecting the hypothetical trace line which gives the greatest consistency along the trace line;

sorting all density differences, between said measured density image and said predicted density image along the chosen trace line, into density bins, and, for bins with a sufficient number of counts, take the average density difference in that bin as an error estimate of the difference between measured and predicted density, in that density interval; and

modifying the media printing software as a function of this array of density errors to control the image quality of subsequent medical image prints.