# Patent

## Title
Converting black to composite black in digital printing

## Abstract

A method of converting black to composite/process black in a digital color print engine. A lightness adjustment is employed for converting input image (O, O, O, Kin) to Ko and initial values of Co, Mo, Yo are set equal to Ko and then converted to C1, M1, Y1, K1 by GCR strategy. Values of Cout, Mout, Yout, Kout are determined by Gray Balance Adjustment for values of C1, M1, Y1, K1 and inputted to the color print engine. The user may disable the conversion to composite black and print black ink/tones if desired. The user may also input different parameters for Lightness Adjustment, Gray Component Replacement and Gray Balance Adjustment.

## Background
BACKGROUND
The present disclosure relates to digital printing in black where it is desired to have a high quality, finished print. Heretofore, digital printing with black ink, for example, with inkjet printers employing frequency modulation type ink-dot spacing have encountered graininess due to ink-dot misplacement. Where dense pure black printing is required for the quality of the print job, it has been desired to improve the quality of the black printing without the increased cost of providing a print engine with a higher number of dots-per-inch of ink deposition. The same problems of graininess have also been encountered where black ink is deposited to provide gray tones/tints.
Thus, it has been desired to provide a way or means of improving the tone of black printing in digital print engines.
BRIEF DESCRIPTION
The present disclosure describes a method or process of converting digital printing in black to a composite of color printing to form a composite black in a manner which eliminates the graininess which may be encountered in digital printing with pure black ink/toner. The method of the present disclosure converts the coordinates of black in color space, i.e. 0, 0, 0, Kin to coordinates C0, M0, Y0 in the Cyan, Magenta, Yellow, color space, and then performs a gray component replacement, GCR, to provide specific coordinates C1, M1, Y1, K1. This is followed by a Gray Balance Adjustment to provide coordinates Cout, Mout, Yout, Kout and inputting these color space coordinates into a digital print engine for creating a composite, or process, black on the print media. Provision is made to adjust the conversion to CMYK color space in accordance with user specified parameters. Provision is also made for user inputting different parameters for any one of the Lightness adjustment, GCR strategy or Gray Balance Adjustment based upon any of several different criteria such as marking resolution, color mode or service type. Provision is also made for the user disabling the composite conversion and direct printing of black ink or toner in the print engine.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block flow diagram of the method of the present disclosure;
FIG. 2 is a graphical presentation of the values for determining Ko from Kin for the particular input image;
FIG. 3 is a graphical presentation of conversion from CMY color space to CMYK coordinate color space; and,
FIG. 4 is a graphical presentation of values of the CMYK coordinates for gray balance adjustment to determine the output values to the print engine.



DETAILED DESCRIPTION
Referring to FIG. 1, the block flow diagram of the method or process of the present disclosure is indicated wherein color space coordinates for the print engine indicated at 0, 0, 0, Kin are inputted to the lightness adjustment function 10 which is illustrated in FIG. 2 and Table I wherein for pixel values of Kin for the input digital image, values of Ko are determined.










TABLE I







Kin
K0



















0
0



1
0



2
0



3
0



4
0



5
0



6
1



7
1



8
1



9
2



10
2



11
3



12
4



13
4



14
5



15
6



16
7



17
8



18
9



19
10



20
11



21
12



22
13



23
14



24
16



25
17



26
18



27
20



28
21



29
22



30
24



31
25



32
27



33
28



34
30



35
32



36
33



37
35



38
37



39
38



40
40



41
42



42
44



43
45



44
47



45
49



46
51



47
53



48
55



49
57



50
58



51
60



52
62



53
64



54
66



55
68



56
70



57
72



58
74



59
76



60
77



61
79



62
81



63
83



64
85



65
87



66
89



67
91



68
93



69
94



70
96



71
98



72
100



73
102



74
104



75
106



76
107



77
109



78
111



79
113



80
114



81
116



82
118



83
120



84
121



85
123



86
125



87
126



88
128



89
130



90
131



91
133



92
135



93
136



94
138



95
139



96
141



97
142



98
144



99
145



100
147



101
148



102
150



103
151



104
153



105
154



106
155



107
157



108
158



109
159



110
161



111
162



112
163



113
165



114
166



115
167



116
168



117
170



118
171



119
172



120
173



121
174



122
176



123
177



124
178



125
179



126
180



127
181



128
182



129
183



130
185



131
186



132
187



133
188



134
189



135
190



136
191



137
192



138
193



139
194



140
195



141
195



142
196



143
197



144
198



145
199



146
200



147
201



148
202



149
203



150
203



151
204



152
205



153
206



154
207



155
207



156
208



157
209



158
210



159
211



160
211



161
212



162
213



163
213



164
214



165
215



166
216



167
216



168
217



169
218



170
218



171
219



172
220



173
220



174
221



175
222



176
222



177
223



178
223



179
224



180
225



181
225



182
226



183
226



184
227



185
227



186
228



187
229



188
229



189
230



190
230



191
231



192
231



193
232



194
232



195
233



196
233



197
234



198
234



199
235



200
235



201
236



202
236



203
237



204
237



205
237



206
238



207
238



208
239



209
239



210
240



211
240



212
240



213
241



214
241



215
242



216
242



217
242



218
243



219
243



220
244



221
244



222
244



223
245



224
245



225
245



226
246



227
246



228
247



229
247



230
247



232
248



233
248



234
249



235
249



236
249



237
250



238
250



239
250



240
250



241
251



242
251



243
251



244
252



245
252



246
252



247
253



248
253



249
253



250
253



251
254



252
254



253
254



254
254



255
255










The system then proceeds to output the adjustment factor Ko for the blackness for the particular input and inputs Ko to step 14 for conversion to Cyan, Magenta, (CMY) color space coordinates. The conversion of step 14 is accomplished by obtaining values of Co=Mo=Yo=Ko which values of Co, Mo and Yo are inputted to a Gray Component Replacement (GCR) strategy at step 16. The GCR at step 16 is accomplished by entering a graph such as FIG. 3 or Table II and obtaining values of CMYK denoted C1, M1, Y1, K1 in FIG. 1 which are then inputted to step 18 for gray balance adjustment.














TABLE II











CMYK








ink







cover
MAX



C
M
Y
K
(%)
Ink






















0
0
0
0
0
0
138


1
1
1
1
0
1


2
2
2
2
0
2


3
3
3
3
0
3


4
4
4
4
0
4


5
5
5
5
0
5


6
6
6
6
0
7


7
7
7
7
0
8


8
9
9
9
0
10


9
10
10
10
0
11


10
11
11
11
0
12


11
12
12
12
0
14


12
13
13
13
0
15


13
14
14
14
0
16


14
15
15
15
0
17


15
16
16
16
0
18


16
17
17
17
0
20


17
18
18
18
0
21


18
19
19
19
0
22


19
20
20
20
0
23


20
21
21
21
0
24


22
22
22
22
0
25


22
23
23
23
0
27


23
24
24
24
0
28


24
26
26
26
0
30


25
27
27
27
0
31


26
28
28
28
0
32


27
29
29
29
0
34


28
30
30
30
0
35


29
31
31
31
0
36


30
32
32
32
0
37


31
33
33
33
0
38


32
34
34
34
0
40


33
35
35
35
0
41


34
36
36
36
0
42


35
37
37
37
0
43


36
38
38
38
0
44


37
39
39
39
0
45


38
40
40
40
0
47


39
41
41
41
0
48


40
42
42
42
0
49


41
43
43
43
0
50


42
45
45
45
0
52


43
46
46
46
0
54


44
47
47
47
0
55


45
48
48
48
0
56


46
49
49
49
0
57


47
50
50
50
0
58


48
51
51
51
0
60


49
52
52
52
0
61


50
53
53
53
0
62


51
54
54
54
0
63


52
55
55
55
0
64


53
56
56
56
0
65


54
57
57
57
0
67


55
58
58
58
0
68


56
59
59
59
0
69


57
60
60
60
0
70


58
61
61
61
0
71


59
63
63
63
0
74


60
64
64
64
0
75


61
65
65
65
0
76


62
66
66
66
0
77


63
67
67
67
0
78


64
68
68
68
0
80


65
69
69
69
0
81


66
70
70
70
0
82


67
71
71
71
0
83


68
72
72
72
0
84


69
73
73
73
1
86


70
74
74
74
1
87


71
75
75
75
2
89


72
75
75
75
3
89


73
76
76
76
3
90


74
77
77
77
4
92


75
77
77
77
5
92


76
78
78
78
5
93


77
79
79
79
6
95


78
80
80
80
7
96


79
80
80
80
8
97


80
81
81
81
8
98


81
82
82
82
9
100


82
82
82
82
10
100


83
83
83
83
10
101


84
84
84
84
11
103


85
85
85
85
12
104


86
85
85
85
14
105


87
85
85
85
15
105


88
85
85
85
17
106


89
85
85
85
19
107


90
85
85
85
21
108


91
85
85
85
23
109


92
85
85
85
25
109


93
85
85
85
27
110


94
85
85
85
29
111


95
86
86
86
31
113


96
86
86
86
33
114


97
86
86
86
35
114


98
86
86
86
37
115


99
86
86
86
38
116


100
86
86
86
40
116


101
86
86
86
42
117


102
86
86
86
44
118


103
86
86
86
46
119


104
86
86
86
49
120


105
86
86
86
51
121


106
86
86
86
53
121


107
85
85
85
55
121


108
85
85
85
58
122


109
85
85
85
60
123


110
85
85
85
62
124


111
85
85
85
64
125


112
85
85
85
67
126


113
84
84
84
69
125


114
84
84
84
71
126


115
84
84
84
73
127


116
84
84
84
76
128


117
84
84
84
78
129


118
84
84
84
80
130


119
83
83
83
82
129


120
83
83
83
85
130


121
83
83
83
87
131


122
82
82
82
90
131


123
82
82
82
92
132


124
81
81
81
95
132


125
81
81
81
97
133


126
81
81
81
100
134


127
80
80
80
102
134


128
80
80
80
104
134


129
79
79
79
107
134


130
79
79
79
109
135


131
79
79
79
112
136


132
78
78
78
114
136


133
78
78
78
117
137


134
77
77
77
119
137


135
77
77
77
122
138


136
76
76
76
124
138


137
75
75
75
126
137


138
74
74
74
128
137


139
73
73
73
130
136


140
72
72
72
132
136


141
71
71
71
135
136


142
70
70
70
137
136


143
69
69
69
139
135


144
68
68
68
141
135


145
67
67
67
143
134


146
66
66
66
145
134


147
65
65
65
147
134


148
64
64
64
149
133


149
63
63
63
151
133


150
61
61
61
153
131


151
60
60
60
156
131


152
59
59
59
158
131


153
58
58
58
160
130


154
57
57
57
161
130


155
57
57
57
162
130


156
56
56
56
164
130


157
55
55
55
165
129


158
54
54
54
166
128


159
53
53
53
168
128


160
52
52
52
169
127


161
51
51
51
170
126


162
51
51
51
172
127


163
50
50
50
173
126


164
49
49
49
174
125


165
48
48
48
176
125


166
47
47
47
177
124


167
46
46
46
178
123


168
46
46
46
180
124


169
45
45
45
181
123


170
44
44
44
182
123


171
43
43
43
184
122


172
42
42
42
185
121


173
42
42
42
186
122


174
41
41
41
187
121


175
40
40
40
188
120


176
39
39
39
189
120


177
39
39
39
190
120


178
38
38
38
191
119


179
37
37
37
193
119


180
36
36
36
194
118


181
36
36
36
195
118


182
35
35
35
196
118


183
34
34
34
197
117


184
34
34
34
198
117


185
33
33
33
199
116


186
32
32
32
200
116


187
31
31
31
202
115


188
31
31
31
203
116


189
30
30
30
204
115


190
30
30
30
205
115


191
29
29
29
206
114


192
28
28
28
207
114


193
28
28
28
208
114


194
27
27
27
209
113


195
26
26
26
210
112


196
26
26
26
210
112


197
25
25
25
211
112


198
25
25
25
212
112


199
24
24
24
213
111


200
23
23
23
214
110


201
23
23
23
215
111


202
22
22
22
216
110


203
22
22
22
217
110


204
21
21
21
218
110


205
20
20
20
220
109


206
20
20
20
221
110


207
19
19
19
222
109


208
19
19
19
223
109


209
18
18
18
224
109


210
17
17
17
225
108


211
17
17
17
226
108


212
16
16
16
227
107


213
16
16
16
228
108


214
15
15
15
229
107


215
14
14
14
230
106


216
14
14
14
232
107


217
13
13
13
233
106


218
13
13
13
234
107


219
12
12
12
235
106


220
11
11
11
236
105


221
11
11
11
237
105


222
10
10
10
238
105


223
10
10
10
239
105


224
9
9
9
240
104


225
9
9
9
241
105


226
8
8
8
241
103


227
8
8
8
242
104


228
7
7
7
243
103


229
7
7
7
244
103


230
6
6
6
245
103


231
6
6
6
246
103


232
5
5
5
247
102


233
5
5
5
248
103


234
4
4
4
249
102


235
4
4
4
249
102


236
3
3
3
250
101


237
3
3
3
251
101


238
2
2
2
252
101


239
2
2
2
252
101


240
2
2
2
252
101


241
2
2
2
253
101


242
2
2
2
253
101


243
1
1
1
253
100


244
1
1
1
253
100


245
1
1
1
253
100


246
1
1
1
253
100


247
1
1
1
253
100


248
1
1
1
254
100


249
1
1
1
254
100


250
1
1
1
254
100


251
0
0
0
254
99


252
0
0
0
254
99


253
0
0
0
255
100


254
0
0
0
255
100


255
0
0
0
255
100









Referring to FIG. 4 and Table III, for the input values of C1, M1, Y1, K1 the output values Cout, Mout, Yout, Kout are obtained in the graph or table and these values of color space coordinates inputted to the print engine as, for example, to a raster image processor.











TABLE III






C
M
Y
K



















0
0
0
0
0


1
1
1
1
1


2
3
3
2
3


3
4
4
3
4


4
5
5
4
5


5
7
6
5
6


6
8
7
5
8


7
9
8
6
9


8
11
10
7
10


9
12
11
8
11


10
13
12
9
13


11
14
13
10
14


12
15
14
11
15


13
17
15
12
17


14
18
16
13
18


15
19
17
13
19


16
21
19
14
20


17
22
20
15
22


18
23
21
16
23


19
24
22
17
24


20
25
23
18
25


21
26
24
19
27


22
27
25
20
28


23
29
27
21
29


24
30
28
22
31


25
31
29
23
32


26
33
30
24
33


27
34
31
25
34


28
35
32
26
35


29
36
33
27
37


30
37
34
28
38


31
38
35
29
39


32
39
36
30
40


33
41
38
31
41


34
42
39
32
42


35
43
40
33
43


36
44
41
34
45


37
46
42
35
46


38
47
43
36
47


39
48
44
37
48


40
50
46
38
49


41
51
47
39
50


42
52
48
40
51


43
53
49
41
53


44
55
51
42
54


45
56
52
43
55


46
58
54
44
56


47
60
55
46
57


48
61
57
47
59


49
63
58
48
60


50
65
60
49
61


51
66
61
51
62


52
68
63
52
64


53
69
64
53
65


54
71
66
54
66


55
73
68
55
67


56
74
69
57
69


57
76
71
58
70


58
78
72
59
71


59
80
74
60
73


60
82
76
62
74


61
83
77
63
75


62
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The system may also include a user input command for disabling the operations of steps 12, 14, 16 and 18 and printing the image monochromatically with black ink or black toner.
The system 10 may also have provision for user inputting or selecting different parameters for any one of the steps 12, 16, 18 such as different marking resolution, color mode or service type e.g. print or copy job.
The gray component replacement at step 16 may also employ a strategy of no black ink/toner in highlight area, (i.e., CMY ink/toner only in highlight) and delaying the use of black ink/toner as late as possible, for example, until mid-tone is reached.
The gray component replacement at step 16 may also employ a strategy of limiting total CMYK ink coverage.
Although the method of the present disclosure has been described for clarity with respect to the use of separate look-up tables (LUT) I, II and III for Lightness adjustment, GCR and Gray Balance adjustment, it will be understood that digitally electronically these tables may be combined into a single look-up table.
The present disclosure thus describes a unique method for converting monochromatic black printing to composite black in a color print engine to provide improved quality of the black print job.
It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.

## Claims

1. A method of converting black to composite black in digital print comprising:
(a) providing a digital color print engine;
(b) using the color print engine for establishing a lightness adjustment factor Ko from black (0, 0, 0 Kin) for the input image;
(c) using the print engine for setting initial values of cyan (Co), magenta (Mo), and yellow (Yo) equal to Ko;
(d) using the print engine for converting Co, Mo, Yo to values of C1, M1, Y1, K1 by GCR strategy;
(e) using the print engine for determining corresponding values of Gray Balance Adjustment Cout, Mout, Yout, Kout for values of Ci, M1, Y1, K1; and,
(f) inputting the values of Cout, Mout, Yout, Kout to the digital color print engine.

2. The method defined in claim 1, wherein the step of establishing a lightness adjustment includes determining Ko from a look-up table of values of black (Kin) versus Ko.

3. The method defined in claim 1, further comprising limiting the ink coverage in the step of converting by GCR strategy.

4. The method of converting black to composite black in digital printing defined in claim 1, wherein the step of converting by GCR strategy includes delaying the output of K1 until mid-tone.

5. The method defined in claim 1, wherein the step of determining Gray Balance Adjustment includes obtaining values of Cout, Mout, Yout, Kout from a look-up table.

6. The method defined in claim 1, wherein the step of converting Co, Mo, Yo to values of C1, M1, Y1, K1, includes obtaining values of C1, M1, Y1, K1 from a look-up table.

7. The method defined in claim 1, further comprising providing for user selection of Kin=255 for printing in black ink/toner only.

8. The method defined in claim 1, further comprising user inputting different parameters for one of Lightness Adjustment, GCR Strategy and Gray Balance Adjustment based upon one of marking resolution, color mode, service type.