GB1048581A - Improvements in or relating to a method and apparatus for making colour prints - Google Patents

Abstract

1,048,581. Photographic colour printing. PAVELLE Ltd. Jan. 17, 1963 [Dec.21, 1961], No. 45873/61. Headings G2A and G2C. A method of making a colour print from a negative or transparency comprises first making a test print by passing light through the negative and then through a test chart consisting of a series of filters of graded density in each of the three component colours, and so ascertaining the necessary exposure time for each of the three colours. Figs. 1 and 2 show the method utilized in a contact printing arrangement, formed as a light-proof box divided into two compartments 1, 5 by a vertical wall 3, which has a slot 4 about half way up. Compartment 1 houses a lamp 2, and compartment 5 is itself divided into three horizontal sub-compartments 6, 7, 8. Sub-compartments 7 and 8 are separated by a negative carrier 13 which can be slid into position from outside the end wall 14. The upper sub-compartment 8 has a glass plate 11 for its top surface, over which a hinged flap 12 can close. Initially, the negative 24 is mounted on its carrier 13 in the position shown in Fig. 1. On the glass plate 11 is laid a test chart 25 and a sheet of light-sensitive printing paper 26, the flap then being closed down. The test chart (or colour wedge) 25 comprises a plate counting three series of filters, one series for each of the component colours, each series being of graded density. In front of slot 4 is mounted a filter slide 17, which has four slots. The first slot 20 is open, the second slot 21 carries a blue filter, the third slot 22, of smaller width, carries a green filter, and the fourth slot 23, narrower still, carries a red filter. The different sizes are to balance the exposure times. Slide 17 is positioned so that the open slot 20 is opposite slot 4. An exposure of predetermined duration is made, the interior walls of sub-compartment 7 being of a light-diffusing nature. The paper 26 is removed and developed, and exposure times for each colour read off corresponding to those filters of each series which have just yielded a positive image. These exposure times are included on the test chart as a calibrated scale in the form of translucent numbers. The negative is now removed, and re-positioned on plate 11, covered by a new sheet of printing paper, in the normal contact-printing arrangement. The filter slide is moved along until the blue filter 21 is over slot 4, and an exposure made of duration determined from the test chart exposure. Exposures are similarly made through the green filter 22 and the red filter 23. The exposures may be controlled by microswitches and time switches actuated by the movement of the filter slide. Figures 3 and 4 (not shown) are of a projection printer adapted for the same method. The method described above is suitable for additive colour printing, but can be modified for subtractive colour printing by replacing the colour filter slide by a colour correction filter unit comprising continuous wedge filters in cyan, yellow and magenta.