This invention relates a thermal recording method using a thermal head. This invention also relates to a thermal recording apparatus.
Thermal recording materials comprising a thermal recording layer on a substrate such as a film, which are hereunder referred to as thermal materials, are commonly used to record the images produced in diagnosis by ultrasonic scanning.
This recording method, commonly referred to as thermal image recording, eliminates the need for wet processing and offers several advantages including convenience in handling. Hence, the use of the thermal image recording system is not limited to small-scale applications such as diagnosis by ultrasonic scanning and an extension to those areas of medical diagnoses such as CT, MRI and X-ray photography where large and high quality images are required is under review.
As is well known, thermal image recording involves the use of a thermal head having a glaze in which heat-generating elements are arranged in one direction and, with the glaze a little pressed against the thermal material (thermal recording layer), the thermal material is relatively moved in the direction perpendicular to the direction in which the glaze extends, and the respective heat-generating elements of the glaze are heated imagewise by energy application to heat the thermal recording layer of the thermal material, thereby accomplishing image reproduction.
In such a thermal recording apparatus, the image processing unit receives image data from an image data supply source such as CT or MRI diagnosis apparatus, and subjects these image data to specified image processing (compensation) jobs, such as sharpness correction, tone correction and the like, to obtain data for the image to be thermally recorded. The thermal head is driven according to these thermal recording image data to heat the respective heat-generating elements, whereupon the image in accordance with the image data supplied from the image data supply source is thermally recorded.
The image processing jobs performed in the image processing unit of the thermal recording apparatus include specifically sharpness correction for edge enhancement of the image; tone correction for producing an appropriate image in accordance with the gamma (.gamma.-) value of the thermal material and individual differences of the thermal recording apparatus; compensation for temperature elevation for adjusting the energy of heat generation in accordance with the temperature of the heat-generating elements; shading correction for correcting the uneven density caused by the shape variability and other factors of the glaze on the thermal head; correction of resistance values for correcting differences between the resistance values of the individual heat-generating elements; and black ratio correction for ensuring that image data representing the same density will yield a color of the same density in spite of the variation in the drop of supply voltage to the thermal head due to the change in the pattern of the images to be recorded; and load variation correction for correcting the stripe-shaped unevenness in density due to the friction force variation in the interface between the thermal material and the thermal head in accordance with the recording density.
In image recording apparatus, image data are usually supplied as numerical data and this is also the case with thermal recording apparatus; image data are supplied as numerical data, say, 10-bit digital data from an image data supply source and subjected to various kinds of image processing jobs such as multiplication of the image data by coefficients of corrections and averaging of the image data.
However, if more than one kind of such image processing jobs that involve direct change of image data are performed, appropriate image processing jobs cannot be accomplished depending on the order of processing and the intended effects of corrections cannot be attained but only reduced image quality of recorded images will sometimes result, thus failing to produce images of the desired quality.
Such a reduced quality of the recorded images can be a serious problem in applications that require the recording of high quality images. Especially, in the applications that require high quality images such as the above-stated medical applications, the reduction in image quality is an obstacle to the viewing of the correct image, potentially leading to a wrong diagnosis.