Reproduced pictures such as printed pictures, reproduced pictures, printer pictures, television (Video) pictures, etc. are produced from original pictures of continuous tone by various types of reproduction techniques, as known well. Incidentally, the term "reproduced pictures" should be interpreted in a broadest sense as described above. In production of these reproduced pictures, it is extremely important to faithfully reproduce the gradation and tone of an original picture on its reproduced picture in a systematic manner. It is however the present state of art that no basic technique has yet been established to permit conversion of an original picture into a reproduced picture rationally and effectively in a systematic manner, in spite of advancement of the techniques for producing reproduced pictures in recent years.
This is attributed primarily to the fact that the technique for converting and processing a non-linear drawing in relation with the density range thereof, which is considered to become a basis of techniques for faithfully reproducing the tone (gradation and tone) of an original picture of continuous gradation on a reproduced picture and further for regulating (correcting or modifying) the tone of an original picture as desired, is totally dependent upon experiences and perception of man. Therefore, the technique still remains in a non-scientific and non-rational state, lacking a foundation of a rational theory therefor.
This will be discussed hereinafter to some extent by way of production of printed pictures as a representative and practical technique.
The conventional technique has no idea to rationally grasp the density characteristic of an original picture in the range of from highlight to shadow areas upon producing a printed color picture as a reproduced picture from a color film original. Approximately 90% of color original pictures are transparent type. Further, the conventional technique is totally dependent upon the experiences and perception of an operator upon determining a correlation of picture characteristics between an original picture and a printed reproduced picture, or upon setting color-separation characteristic curves (equally called "color-separation characteristic curves" or "halftone characteristic curves"), which determine a correlation between an original picture of continuous tone and a printed reproduced picture in halftone.
Upon producing a printed color picture in halftone from an original color picture, the original color picture is subjected to color separation by a color scanner to make color plates (C, M, Y and K, in general).
The color scanners or total scanners, which are highly mechatronized, are very expensive systems. One of the problems hold in the present field of art is that an operation rate of such scanners is still on an order as low as about 30% on average. Such the low operation rate of scanners is attributed to the fact that scanner-setting takes a considerable long time besides a considerable number of original pictures require rescanning because of unstable and unsatisfactory quality of the resulting reproduced picture obtained through color-separation.
Considering this in the light of a technical view, a plurality of technical elements in the color-separation work, for example color correction, density gradational conversion, etc., are not systematized in a good coordination, while color scanners highly advanced in mechatronics are used as working means for color separation, as previously described. The low operation rate of color scanners is attributed to the above fact. Concerning two technical elements, i.e., color correction and density tonal conversion, the color correction has been investigated closely in a scientific manner, as seen in the Masking equation or Neugebauer equation. On the other hand, density tonal conversion remains in a state lacking a rational theory therefor, thus heavily dependent upon experiences and perception of man. Namely, the problem is that which size of a halftone dot should be corresponded to a given picture element of an original color picture. Under such circumstances, machines and systems for color separation have been developed, although a basic technique for designing machines and systems is still in an immature level. Additionally, the practical work heavily depends on the experiences and perception of an operator, while using such expensive and highly advanced electronic color-separation system. From the above reasons, constant supply of printed color pictures having stable qualities is difficult in the present state. Specifically, there exists a serious problem in the case that a color original has been produced under in appropriate conditions such as photographing, exposing and developing conditions, or a color original has color-fog thereon. Namely, the conventional techniques fail to provide rational color separation work to cope with such the color originals of non-standard picture qualities. Furthermore, there exist another problems in the conventional techniques such as a low operation rate of scanners, unstable quality of a reproduced picture, increase of rescanning work, etc. as previously mentioned.