Radiation imagery chemistry: process – composition – or product th – Plural exposure steps
Patent
1985-10-29
1988-07-19
Kittle, John E.
Radiation imagery chemistry: process, composition, or product th
Plural exposure steps
430332, 430333, 430396, 430962, G03C 500
Patent
active
047585021
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to contrast masking in photographic processes. In many photographic processes an original, usually transparent, is illuminated, and an image is thrown on a photosensitive material to create a reproduction of the original. In many cases the range in optical density between the lightest point and the darkest point of the original (or in practice between the lightest point and the darkest point which retain detail, rather than between any totally white or black areas), known as the contrast range of the original, is too great to provide the optimum appearance of the reproduction. This is especially, but not exclusively, the case when a transparent original is being used to make a reproduction intended to be viewed by reflected light. If the contrast range is too great, then either the dark parts of the reproduction are too dark for detail to be seen clearly or the light parts are so light that detail is "washed out".
In other photographic processes the original may not be transparent, for instance it may be a print, or a scene which is being photographed.
If the contrast range in the original is too great for an optimum reproduction, the photographic craftsman has several ways of compensating for this. He may "dodge" or "burn in" selected areas of the reproduction by hand (darken or lighten the areas by selective covering and exposing). However, this is difficult and time-consuming, and requires considerable skill to do well. An alternative method is to form a contrast mask. A contrast mask is a negative image of the original, and as such its greatest optical density is in those areas where the original has its least optical density, and vice versa. If the contrast mask and the original are placed together in perfect alignment, the composite will retain the detail of the original perfectly, while having a contrast range which is less than that of the original. By controlling the exposure during formation of the mask its optical density range can be controlled, and thus the contrast range of the composite can be controlled to provide any desired preselected value. Typically the composite of contrast mask plus original may have a contrast range of 2.4, compared with a range of perhaps 2.8 for the original alone.
To form a contrast mask, the original is placed in contact with a piece of unexposed monochrome negative film, registration holes or the like may be punched through them, and then they are exposed to the amount of light required to form a mask of the desired density range. The monochrome film is then separated from the original and developed to form the contrast mask. Finally the contrast mask and the original are placed back together again and aligned by means of the registration holes or the like or registered by eye, and the composite thus formed is used to create the reproduction in the normal way.
This process of contrast masking is tedious and time-consuming. Additionally it may be difficult to replace the mask in perfect register with the original, and the mask may shrink a little during developing making perfect alignment over the whole area of the original impossible. Finally, any defects in the mask, eg. resulting from dirt, add to the defects which will appear in the reproduction. In spite of these drawbacks, the process of contrast masking is very widely used, as the effect on the quality of a reproduction of contrast range reduction is considered highly desirable in high quality photographic applications.
BACKGROUND ART
In the 1950's a proposal was made by Dwin R Craig and John N Street that a photographic contrast mask should be made using a metachromatic oil use. This material had a photochromic property, in that exposure of it to blue light caused it to turn a brillant blue, and exposure to yellow light turned the blue material colourless. Craig and Street proposed that a body should be made bearing a film of this oil or a layer of micro-encapsulated such oil. The body was to be aligned with a transparency and then illuminated with blue l
REFERENCES:
patent: 2203652 (1939-01-01), Ehrenfried
patent: 3105761 (1958-09-01), Foris
patent: 3160504 (1964-12-01), Montani
patent: 3442648 (1969-05-01), Smith
patent: 3510305 (1970-05-01), Craig et al.
patent: 3973966 (1976-08-01), Flannery et al.
patent: 4321321 (1982-03-01), Moore
D. A. Spencer, The Focal Dictionary of Photographic Technologies, 1973, p. 443.
Dees Jos,e G.
Image Master Limited
Kittle John E.
LandOfFree
Photographic contrast masking with a photochromic body does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Photographic contrast masking with a photochromic body, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Photographic contrast masking with a photochromic body will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-596929