Method and Apparatus for Forming Synthesized Image

1. Field of the Invention

The present invention relates to a method and apparatus for forming a synthesized image which is capable of combining a plurality of images and outputting a resultant synthesized image to an image display device or a printer, or of storing it in a memory unit.

2. Description of the Prior Art

Conventionally, various methods of combining a plurality of images and outputting the results have been proposed. Image synthesis or the multiplex output of a plurality of images to one picture screen has been commonly practiced lately in a wide range of areas, including high-performance workstation and home-use personal computers.

With conventional methods, when a plurality of images, e.g., two images, are combined and output from an output device such as a display device, overlapped parts of the synthesized image are each selectively constituted by the part representing the most significant image, i.e., it is impossible to leave a space for a subordinate image in the overlapping part and see it through that space.

Accordingly, an object of the present invention is to provide a method and apparatus for forming a synthesized image which can eliminate the problem described above.

In one embodiment, the present invention provides a method and apparatus which are capable of forming a checkerboard pattern of a synthesized image from a plurality of images (throughout the specification, abstract and claims, the phrase "in checkerboard fashion" means "in a two-dimensional array comprising a plurality of lines and, transverse to the lines, a plurality of columns, each line and each column having a plurality of regions of one type and a plurality of regions of a second type alternating in both directions with the regions of the one type").

In another embodiment, the invention further provides a method and apparatus which are capable of eliminating the Moire-like dot pattern which may be generated when dot images are combined.

Other objects of the present invention will become clear from the following description taken in conjunction with the accompanying drawings.

FIG. 1 is a block diagram of an image synthesizing apparatus;

FIG. 2 shows a checkerboard pattern used to explain an embodiment of the present invention;

FIG. 3 is a circuit diagram of an image synthesis unit;

FIG. 4 is a flowchart of an embodiment of a first method of synthesizing an image; and

FIG. 5 shows the allocation of memory cells in a video memory.

FIG. 1 shows an embodiment of an image synthesizing apparatus according to the present invention, which is capable of synthesizing an image in a checkerboard fashion from two images. The image synthesizing apparatus includes image memories 1, 2 each of which stores one image, an image synthesis unit 3 for synthesizing an image in a checkerboard fashion, and a video memory 4 for storing a synthesized image which is to be output to a display device 5 or a printer 6, or which is to be stored in a memory unit 7.

The image synthesis unit 3 uses two methods for storing picture elements in the video memory 4: a first method in which picture elements constituting the images stored in the image memories 1, 2 are selectively stored in the video memory 4; and a second method in which a picture element of an image which has been stored in the video memory 4 is smoothed by performing a convolution on that picture element and the picture elements located adjacent thereto, the result again being stored in the video memory 4.

The first method will be described below in detail, under the assumption that the memories 1 and 2 store data representing picture elements in such a way that it can be regarded as a two-dimensional array.

In the picture image synthesis, data is selected from two images in groups of at least one picture element to form a synthetic image of a checkerboard pattern, as shown in FIG. 2. For convenience of description, it is assumed that each constituent of the checkerboard corresponds to one picture element, i.e., that each of the squares in the pattern shown in FIG. 2 corresponds to one picture element in the video memory 4, and the hatched squares contain data constituting picture elements stored at the corresponding positions in the image memory 1, while the blank squares contain data constituting picture elements stored at the corresponding positions in the image memory 2.

FIG. 3 is a circuit diagram of the image synthesis unit 3. The image synthesis unit comprises a CPU 31 which performs an image synthesis operation, a keyboard 32 from which coordinates of a synthesized image or of picture elements in the two original images to be combined are input and from which various instructions are given, a ROM 33 which stores an operational program which is shown in FIG. 4, and a RAM 34 which temporarily stores data required for the operations conducted by the CPU 31.

The operation of the image synthesis unit will be described hereinbelow with reference to the program flowchart shown in FIG. 4.

The operation starts by inputting initial values for i, i', i", j, j', and j" from the keyboard in step 41, where (i, j) designate the coordinates in the video memory 4 at which the selected data is stored, while (i', j') and (i", j") denote the coordinates in the image memories 1 and 2, respectively. VM(i, j) denotes data values of a picture element to be stored in the video memory 4, while IM1 (i', j') and IM2 (i", j") denote data values of picture elements which have been stored in the image memories 1, 2, respectively. In step 42, IM1 (i', j') and IM1(i'+1, j'+1) are stored in VM(i, j) and VM(i+1, j+1), respectively. Then, in step 43, IM2(i"+1, j") and IM2 (i", j"+1) are stored in VM(i+1, j) and VM(i, j+1), respectively. Subsequently, i, i' and i" are each incremented by two, and the same operations are repeated. This set of operations is repeated until one scan, in which two lines are scanned at the same time in the first direction (in steps 42 to 45), is completed. In step 47, the values of j, j' and j" obtained when one scan in the main direction has been completed are each incremented by two, and i, i', i" are initialized ready to scan the next two lines. All the remaining lines are then scanned in this way to complete the processing of the specified image area.

With the arrangement described above, it is possible to synthesize an image in such a manner that it forms a checkerboard pattern with its constituent adjacent picture elements being selected from different images, as shown in FIG. 2, and stored in the video memory 4. The data stored in the video memory 4 may then be displayed on the display device 5, recorded by the printer 6, or stored in the memory unit 7.

The second method of forming a synthesized image by image synthesis unit will be described next. When original dot images are combined into a dot image, Moire patterns are generated owing to distortions of spatial frequencies. If the dot images are combined by the first method, the resultant synthesized image therefore has intruding patterns which resemble Moire patterns, and which reduce the image quality. In order to remove these patterns, the resultant synthesized image is smoothed by means of convolution.

FIG. 5 shows the allocation of memory cells in the video memory 4. Convolution is performed on, for example, VM(i, j) and the eight picture elements located adjacent thereto. Data representing the picture element to be smoothed, VM'(i, j), can be obtained by the following equation: ##EQU1##

The thus-obtained data VM'(i, j) is then stored in another video memory 4'.

The operation expressed by equation (1) is performed on all data (i, j) stored in the video memory 4 in step 50, after step 46 is executed.

At that time, if there are no peripheral picture elements for VM (i, j), the missing picture element is substituted from the picture element located adjacent thereto or the data VM(i, j).

If there are a plurality of images to be combined, a predetermined number of picture elements can be output from each of the picture images in turn for each picture element group.

In the embodiment described above, picture elements stored in the video memory 4 form a checkerboard pattern. If their phases are the same, it is possible to form a striped pattern.

Each constituent of the checkerboard obtained in the above-described embodiment corresponds to one picture element. If the units of the numbers of picture elements to be selected from each of the image memories 1 and 2 are independent of each other, it is possible to express depth by the synthesized image.

In the embodiment described above, two images are combined in a checkerboard fashion. However, it is possible to synthesize an image from three or more images.

As will be understood from the foregoing description, according to the present invention, an image can be synthesized from a plurality of images by a simple method in which picture elements are selected from each of those images in groups of picture elements.

This invention has been described with reference to a preferred embodiment. Obvious modifications and alterations may be made without departing from the spirit and scope of the invention as set forth in the appended claims.