Digital BW, The Print

Roy Harrington wrote:
...
>> I mentioned to you that, at least at 2880dpi, the QTR 100% ink limit 
>> calibration test produced an anomalous result at the 50% step with the 
>> density being less than at 45%. It was therefore necessary to 
>> interpolate this density. As you surmised this appeared to be a specific 
>> dithering problem that only occurred at this step.
>> 
>> If you then chose an ink limit of 70% say and reprinted the 21-step you 
>> wouldn't notice it because none of the steps would be at 71.4% (50/70).
>> 
>> The theory was therefore that the series of bands in Graham's test image 
>> were caused by each ink (for which you had different ink limits) going 
>> across it's own 50% mark.
>> 
>> If it is caused by this you should be able to work out where each band 
>> will occur by looking at each ink's limit and calculating where it 
>> crosses the 50% mark.
>> 
>> There is contrary evidence to this. For example, at 2880dpi my ink 
>> limits are often beneath 50% yet when I printed the test image I also 
>> saw banding. Also you would think that the phenomenon would have been 
>> frequently noticed in images with gentle gradations at which these ink 
>> limit boundaries are crossed. On the other hand these bands are 
>> particularly noticeable in Graham's test but not on a linear ramp so 
>> maybe we wouldn't notice them anyway.
>> 
>> So, inconclusive but I'd be interested to hear if any other QTR users 
>> have noticed these odd readings during the calibration test.
>> 
>> Howard
>>
> 
> Howard,
> 
> I'm not sure what printer you are using.  The one thing that gives anomalies
> is too much ink. I can't imagine much else especially at 2880dpi.  But if you 
> have some other than that I'd like to see what it is.
> 
> Roy

Roy

I'm using a 2100. This happens with the 100% ink calibration at the 50%
step for all ink positions. For example these are the density readings
for the latest ink/paper combination I've been making curves for:

	K	C	M	Y	LC	LM	LK
0	0.04	0.04	0.04	0.04	0.04	0.04	0.04
5	0.42	0.32	0.27	0.08	0.17	0.15	0.08
10	0.72	0.53	0.44	0.12	0.27	0.24	0.11
15	1.01	0.74	0.61	0.16	0.38	0.33	0.15
20	1.23	0.91	0.75	0.2	0.47	0.42	0.19
25	1.4	1.03	0.86	0.23	0.55	0.49	0.22
30	1.51	1.13	0.96	0.27	0.63	0.56	0.26
35	1.58	1.2	1.02	0.3	0.69	0.61	0.29
40	1.63	1.25	1.08	0.33	0.74	0.66	0.31
45	1.68	1.3	1.14	0.36	0.8	0.72	0.34
50	1.68	1.31	1.13	0.36	0.8	0.71	0.33
55	1.72	1.35	1.23	0.41	0.87	0.8	0.39
60	1.73	1.37	1.26	0.43	0.9	0.82	0.4
65	1.74	1.38	1.29	0.45	0.93	0.85	0.42
70	1.75	1.39	1.3	0.47	0.95	0.87	0.43
75	1.75	1.39	1.31	0.48	0.98	0.89	0.45
80	1.75	1.4	1.33	0.5	1	0.92	0.46
85	1.76	1.4	1.33	0.51	1.02	0.94	0.48
90	1.75	1.4	1.34	0.52	1.05	0.95	0.49
95	1.75	1.4	1.34	0.54	1.07	0.97	0.5
100	1.75	1.4	1.34	0.56	1.08	0.99	0.52

I'm sure I've read other posts about this in the past but for the moment 
can only find message 69526 which relates to a R200 and 1440dpi and may 
or may not be related:

http://tech.groups.yahoo.com/group/DigitalBlackandWhiteThePrint/message/69526

The exact settings I use are 2880dpi, Better, Adaptive Hybrid.

It's not a big deal - as I said, I've never noticed the effect in an 
actual image and its easy enough to interpolate the 50% step at the 
calibration stage. I just thought this might account for the bands that 
are apparent in the circular test image.

Howard