Durst M 670 COLOR Manuale operativo - Pagina 10

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You now have to eliminate this colour cast by an appropriate

filter correction. The colour mixing head has three built-in

colour filters for this purpose:

(1) Yellow (Y)

(2) Magenta (M)

(3) Cyan (C).

The other three primary colours (red, green and blue) are

obtained by combining two filter colours in the colour mixing

head:

Red: By setting equal values of yellow and magenta

Green: By setting equal values of yellow and cyan

Blue: By setting equal values of cyan and magenta.

For example: 10 red

10 yellow + 10 magenta.

Before you use these filters or filter combinations you must

know something of their effect. So remember the following

filter rules:

Filter correction effects when enlarging colour negatives

Rule 1:

A colour cast in an enlargement from a negative is removed

by a filter or filter combination of the same colour. In an

enlargement from a positive transparency a cast is removed

by a filter (or combination) of the complementary colour.

Rule 2:

Excessive correction causes a cast in the complementary

colour; reducing that filtration again restores colour balance.

Rule 3:

Use only one or two, never three filter colours. A third filter

colour adds grey density which does not modify the filter

effect but only increases the exposure time required.

Rule 4:

The stronger the cast, the higher must be the corrective filter

density.

Required correction on

Effect in print of

Colour cast in print

Effect in print

colour mixing head

over-correction

+ Yellow

Yellow cast

Less yellow

Blue cast

Magenta cast

+ Magenta

Less magenta

Green cast

Red cast

Cyan cast

+ Yellow + magenta (=red)

Less red

Cyan cast

Less cyan

+ Cyan

Red cast

Blue cast

Less blue

Yellow cast

+ Magenta + cyan (= blue)

Less green

Magenta cast

Green cast

+ Yellow+cyan (=green)

Filter correction effects in enlargements from positive colour transparencies

Colour cast in print

Required correction on

colour mixing head

Effect in print

Effect in print of

over-correction

Yellow cast

+ Magenta + cyan

Less yellow

Blue cast

Magenta cast

+ Yellow+cyan

Less magenta

Green cast

Red cast

+ Cyan

Less red

Cyan cast

+ Yellow+magenta

Less cyan

Red cast

Blue cast

+ Yellow

Less blue

Yellow cast

Green cast

+ Magenta

Less green

Magenta cast

Cyan