Digital BW, The Print

Joost Horsten wrote:
> --- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Kevin Bradford" 
> <bradford@...> wrote:
>>
>> --- In DigitalBlackandWhiteThePrint@yahoogroups.com, Howard Shaw
>> <glassman@> wrote:
>> > I'd be interested to know if you also see this banding with ABW for 
>> > example or does it only occur with QTR?
>> > 
>> > Howard
>> >
>> 
>> The ABW print did not show any banding, it was very smooth. 
>> 
>> Kevin
>>
> 
> 
> Howard,
> 
> This seems to support your theory we discussed off-line. Perhaps you 
> could elaborate here?
> 

Joost

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