Since the early eighties practical use of light-sensitive tabular silver halide grains or crystals has become common knowledge for anyone skilled in the art of photography. From Eastman Kodak's basic patents relied thereupon those related with the preparation of {111} tabular silver halide grains, sensitivity increase by spectral and chemical sensitization, and coating in a light-sensitive silver halide photographic material, more particularly in a forehardened duplitized radiographic material showing improved covering power for tabular grains having a thickness of less than 0.20 μm as described in U.S. Pat. No. 4,414,304 and in the patents corresponding therewith in Japan and in the European countries, it becomes clear that problems encountered by making use of such grains are related with image tone and developability as has also been set forth in U.S. Pat. No. 5,595,864.
In radiographic applications the film materials are coated with relatively high amounts of silver, in order to provide a suitable sensitometry even if a low radiation dose is applied to the patient as is always desirable. Although the use of {111} tabular silver halide grains permits coating of lower amounts of silver, if compared e.g. with grains having a more globular shape as applied before practical application of said tabular grains, there remains the need to provide an acceptable image tone after development of materials having light-sensitive silver halide layers containing said tabular grains. Reduction of thickness of the {111} tabular grains coated in a radiographic film material hitherto, although providing a higher covering power, remains unambiguously related indeed with the occurrence, after processing of such materials, of diagnostic images having an unacceptable reddish-brown image tone for radiologists as image tone and image quality are closely related with each other in the specific context of examination of diagnostic images. Measures taken in order to get a shift in image tone from reddish-brown to the desired bluish-black color of the developed silver, well-known from the state-of-the-art are hitherto unsatisfactory. Coating light-sensitive emulsion layers on a blue base as in U.S. Pat. No. 5,800,976 makes increase minimum density, a phenomenon which is interpreted by the radiologist as an undesired increase of “fog density”. Incorporation in the other layers of the film material of such dyes or dye precursors providing blue color directly or indirectly (by processing and oxidative coupling reactions) are e.g. known from U.S. Pat. Nos. 5,716,769 and 5,811,229 and EP-A 0 844 520, and JP-A 10-274 824 respectively and causes the same problems as set forth hereinbefore, moreover showing, in the worst cases, staining of the screens with blue dyes diffusing from the material onto the screen, with residual color of dyes due to uncomplete removal of said dyes in, nowadays desired, rapid processing steps and problems related with criticality of generation of imagewise developed blue colored silver and preservation characteristics of the material.
Radiographic elements exhibiting increased covering power and colder image tones have been published in U.S. Pat. Nos. 5,795,795; 5,800,976 and 5,955,249.
More recently very effective measures in order to improve image tone have been described in EP-A's 1 103 847, 1 103 848, 1 103 849 and 1 103 850.
The stringent demand thus remains to get a desired blue-black image tone of a diagnostic image without disturbing residual color obtained after processing of the radiographic light-sensitive silver halide film material, wherein the said material has suitable preservation characteristics before use. Besides attempts in order to optimize the relationship between image tone, covering power and improved preservation characterics made in EP-A's 1 262 824 and 1 262 825 and in U.S. Pat. Nos. 6,348,293; 6,346,360 and 6,342,338; U.S. Pat. No. 4,740,454 is referred to as relating to a silver halide photographic material having improved sharpness over a wide range from the high frequency area to the low frequency area.