1. Field of the Invention
This invention relates to color photographic materials and in particular to color negative photographic materials which provide a color image having improved color reproduction and tone reproduction upon exposure of the materials to either ambient light (such as daylight) or electronic flash light (strobe light).
2. Description of the Prior Art
Recently, demands for color negative photographic materials having better photographic properties has become stronger and in particular much better improvement in color reproduction and tone reproduction is desired. With the popularization of the strobe and cameras with a built-in strobe, opportunities for taking photographs using strobe light, i.e. electronic flash light have increased, and therefore a strong desire has arisen for a color negative photographic material which provides a color image having excellent color reproduction and tone reproduction.
When color negative photographic materials of the prior art are used to take photographs using electronic flash light, the following problems concerning color image quality arise: First, the color film does not reproduce colors as the eye sees them and a printed paper obtained from the negative film appears bluish. Second, the tone of the image is hard, and the tone of a human face, which is considered to be very important, is not adequately reproduced. Sometimes, delicate shadows on an object such as the face become entirely whitish (so-called "blow out") on the color print.
It is considered that the first problem is due to the high color temperature of flash light. For example, FIG. 1 shows energy distributions of flash light of the built-in strobe within a camera (AUTOBODY (trademark) produced by CANON) and daylight in fine weather. As seen from FIG. 1, flash light is high in blue light energy component and low in red light energy component as compared with daylight. Therefore, a negative film upon exposure to flash light provides a color print having color balance inclined to bluish and cyanish color as compared with that provided upon exposure to daylight.
It is generally known in the art of color photographic materials that the spectral sensitivities of blue, green and red sensitive layer can be brought near to each other in order to decrease the dependency on light-source color temperature. However, it is undesirable to bring the spectral sensitivity near to each other because color saturation is lowered.
It is considered that the second problem is due to the fact that the strobe is nearly a point light source which increases the difference in color density between light and dark areas in the object, and therefore the tone of a picture on the film appears hard. Tone reproduction can be softened by decreasing gradation of light-sensitive materials. But such lightsensitive materials provide a too soft, or undesirable "dull" picture, when used for photographing without electronic flash light, including photographing under ambient light of cloudy or rainy days.
The inventors of this invention studied ways to overcome these problems inherent in taking flash pictures. They found that natural color reproduction and excellent tone reproduction can be accomplished in flash light photography without impairing the picture quality obtained in ambient light photography (i.e. regular photography) by finely controlling the high-intensity reciprocity failure of each light-sensitive layer of a color negative film. First, it is necessary to make the high-intensity reciprocity failure of each light-sensitive layer larger by the desired degree. By this means, it is possible to soften picture gradation upon high-intensity short-time exposure such as in flash photography and to realize excellent tone reproduction, with hard picture gradation in regular photography being maintained at the desired degree. Second, it is essential to make the high-intensity reciprocity failure of the blue sensitive layer larger than that of the green sensitive layer and that of the red sensitive layer smaller than that of the green sensitive layer. By this, it is possible to compensate the deviation of color balance due to the high color temperature of flash light and consequently to obtain natural color reproduction in flash photography.
Extensive studies on high-intensity reciprocity failure characteristics of silver halide light-sensitive materials have been reported. There is described in "The Theory of the Photographic Process", 4th ed. pp. 140-142 edited by T. H. James that the high-intensity reciprocity failure could be controlled by the halide composition, pH and pAg of silver halide emulsion, chemical sensitizer, etc. However, it has never been described or suggested that it will be possible to impart suitability for flash photography to a color negative light-sensitive material by finely controlling the high-intensity reciprocity failure of each light-sensitive layer of the material in light of the characteristics of flash light previously described.