1.  Field of the Invention
The present invention relates to an image intensification process for a photographic element having image-wise distributed therein a material possessing a catalytic action with a cobalt (III) complex.  More particularly, the invention relates to a process of preventing the formation of fog in a color photographic process by removing fogging components from a photographic processing solution through a hydrophobic porous diaphragm. 
2.  Description of the Prior Art
It is known that after exposing a photographic material containing light-sensitive metal salts, images of a catalytically active metal belonging to Group VIII, Group VIa or Group Ib of the periodic table by chemical development or physical development and dye images or tanning images can be formed in the photographic element using a reducing agent or using a reducing agent and color couplers in the presence of hydrogen peroxide or a hydroperoxide.  For example, descriptions of this image forming method appear in German Patent Applications (OLS) Nos.  1,813,920 (corresponding to U.S. Pat.  No.  3,674,490), 1,950,102, 1,995,901, 1,961,029 (corresponding to U.S. Pat.  No.  3,684,511), 2,044,833, 2,044,993 (corresponding to U.S. Pat.  No.  3,761,265), 2,056,360 (corresponding to U.S. Pat.  No.  3,776,730), 2,056,359 (corresponding to U.S. Pat.  No.  3,765,890) and 2,120,091 (corresponding to U.S. Pat.  No.  3,817,751) and Japanese Patent Applications Nos.  128,327/74 (corresponding to German Patent Application (OLS) No.  2,549,837) and 139,917/74 (corresponding to German Patent Application No. ( OLS) 2,549,837). 
In the field of color photography, a color photographic material prepared by coating on a support silver halide emulsions having incorporated therein couplers such as a cyan coupler, yellow coupler, and a magenta coupler using various technique is image exposed and then subjected to a series of processings for reproducing color images in the photographic material. 
The fundamental processing steps of these processings are a color development step and a silver removal step.  That is, in the color development step, silver halides of the exposed silver halide color photographic material are reduced by a color developing agent to form silver images and at the same time the oxidized color development agent reacts with the couplers to provide dye images.  Thereafter, the color photographic material is subjected to a silver removal step, wherein the silver formed in the previous step is oxidized by the action of an oxidizing agent (also called a "bleaching agent"), dissolved then by a complexing agent for silver ions usually called a "fixing agent", and removed from the photographic material.  Thus, dye images only remain in the photographic material.  In practical photographic processing of color photographic materials, auxiliary processing steps are employed for maintaining the desired photographic and physical properties of color images or improving the storage stability of the color images in addition to the above-described two fundamental steps of color development and silver removal.  For example, a hardening bath for preventing the photosensitive emulsion layers of color photographic materials from being excessively softened during processing, a stop bath for effectively stopping the development reaction, an image stabilization bath for stabilizing images, and a bath for removing a backing layer from the support of a photographic material, are illustrative of these auxiliary processing steps. 
This kind of the color photographic processing has already been practiced on a world-wide basis in the photographic art since 1940. 
The color photographic material used in the color photographic process as described above generally contains silver in an amount of about 1 to about 15 g per square meter of the color photographic material in the form of silver halide.  For example, reflection-type image forming materials represented by color papers usually contain about 1 to about 2.5 g of silver per square meter of the photographic material and photographic materials such as color photographic negative films and color photographic reversal films contain about 3 to about 9 g of silver per square meter of the photographic material.  This amount of silver is necessary for obtaining a sufficient dye image density but if the amount of silver required can be reduced, the advantage is large from the standpoint of conservation of silver as a resource as well as reduction of the manufacturing cost of the photographic materials. 
U.S. Pat.  No.  3,674,490 discloses a process of reducing the amount of silver halides used in photographic materials using a color intensification process.  According to the process of the patent, metal images distributed in an image-wise manner in the photographic material activate hydrogen peroxide or another peroxide as a catalyst to cause an oxidation reaction to occur, whereby dyes are formed and color images are ultimately formed.  In this case, the amount of the metal images may be very small since the metal images may act as a catalyst and hence when silver is employed for such metal images in the process, a desired color density can be obtained using a greatly reduced amount of silver salts as compared with that used in gelatino silver halide emulsions of conventional types.  In this process, the peroxide is used in the intensification step added as a subsequent step to a development step represented by color development. 
However, this process has various disadvantages.  For example, peroxides such as, for example, hydrogen peroxide, etc.,  are very unstable in aqueous solution.  In particular, a peroxide is very unstable when a developer is carried over and is readily decomposed to reduce greatly the image intensification effect.  Furthermore, the intensification treatment with a peroxide is accompanied by the formation of severe amount of fog.  Still further, peroxides have adverse effects on living bodies and a possibility of an explosion occurring exists.  Hence, the handling of these materials requires specific care. 
U.S. Pat.  Nos.  3,826,652, 3,834,907, 3,748,138 and 3,765,891 describe a process of reducing the amount of silver halides used in photographic materials using another novel color intensification process.  According to the process as described in the above patents, metal images image-wise distributed cause an oxidation-reduction reaction by a cobalt (III) complex such as, for example, [Co(CH.sub.3).sub.6 ]Cl.sub.3 as a catalyst, to occur to form dyes and to provide color images.  However, this process also has a serious disadvantage in that if developer components such as a developing agent are present together with the cobalt (III) complex, fog forms markedly on the color photographic images. 
Depending on the manner of processing, the image intensification process using a cobalt (III) complex can be classified fundamentally into the following three types of processes.  That is, (1) a three bath processing comprising a color development, an intensification, and a blix; (2) a two bath processing comprising a color development-intensification and a blix; and (3) a mono bath processing comprising a color development-intensification-blix.  Among these processings, the processing solutions in the two bath processing and the mono bath processing are very unstable since in these cases a cobalt (III) complex is present together with developer components in the processing solutions and, thus, if these processings are not performed at room temperature (e.g., about 20.degree.-30.degree.  C.) within a few hours, the image intensification effect is reduced and a marked degree of fog forms.  In the three bath processing wherein the developer and the intensification solution are used separately, it is expected that the processing compositions can be used or stored for a longer period of time.  However, in the three bath processing, a water washing step is not employed between the color development and the intensification step or water washing or rinsing is carried out, if employed, in a very short period of time and hence in the running processing, about 10 to 30% of the development components usually are carried over into the intensification solution from the developer.  Therefore, the three bath processing is also accompanied by the formation of a severe degree of fog. 
In order to overcome the above-described difficulties caused by the use of the cobalt (III) complex, it is most preferred to incorporate the cobalt (III) complex in color photographic materials.  These techniques are described in, for example, Japanese Patent Applications Nos. ( OPI) 84,229/74 (corresponding to German Patent Application No. ( OLS) 2,357,695), 84,239/74 and 97,614/74 (corresponding to U.S. Pat.  No.  3,847,619).  However, this system involves another serious disadvantage in that the sensitivity of the silver halide is greatly reduced. 
As another method of overcoming the above-described difficulties, incorporation of an organic anti-foggant in the processing solution containing the cobalt (III) complex has been proposed.  Such organic anti-foggants which can be used include known nitrogen-containing heterocyclic compounds and mercapto-substituted nitrogen-containing heterocyclic compounds.  The addition of these heterocyclic compounds may reduce the formation of fog to some extent but, at the same time, reduces greatly the image density formed.