A display control circuit includes a window coordinate data memory for storing window coordinate data which specifies a window region in a display region of a displaying device for displaying an image in accordance with address data and display data, a mask data generator for generating mask data for distinguishing the window region from the display region in accordance with the address data and the window coordinate data, and an operating device for generating display data input to the displaying device by operating the mask data and the display data corresponding to every address data input to the displaying device.

A processing system is provided that includes an external device connected to a processor. The external device has the capability of responding to external device commands wherein each of these external device commands is performed within at least one fixed time cycle. The processor provides these external device commands and, further, includes the means for executing instructions that not only specify the external device commands but also specify at least one internal command to be performed by the processor simultaneously with the performance of the external device command and within the same fixed time cycle. In the disclosed embodiment, a graphics display system is provided that includes a system processor, a graphic processor, a graphics memory and a display device. The graphics processor receives instructions from the system processor which specifies commands to be executed by both the graphics processor and the graphics memory. Each graphics memory command is executed within a fixed time cycle simultaneously with the execution of a corresponding graphics processor command executed within the graphics processor.

A noise analyzer apparatus for a video signal produced by an X-ray imaging system corresponding to an image generates, in response to vertical and horizontal sync pulses, a two-level gating signal which is at a predetermined level solely during the times that intensity information contained in the video signal corresponds to pixels in an adjustably positionable window area of the image. A gated noise measuring circuit responsive to intensity information contained in the video signal and to the gating signal forms a signal which is a measure of a noise content solely within the window area of the image. A signal combiner combines the video signal and a signal derived from the gating signal to produce an augmented video signal containing in its intensity information a marker indicating the location of the window area. The augmented video signal is fed to a display from which the operator may observe the repositioning of the window area in the image as vertical and horizontal time delays introduced in the noise analyzer are adjusted.

An image processing method and system wherein the virtual storage concept is introduced into the storage and management of image data so as to be adapted to an image processing. Data representing an image is stored on a block basis as data blocks corresponding to image strips in a virtual image, in a first storage device, having a plurality of storage blocks, corresponding to a virtual storage, and the data blocks to be processed are fetched from the first storage device into a second working storage device, having a smaller number of storage blocks than the plurality of storage blocks in the first storage device, corresponding to real storage, to perform image processing.