DTP 70 repeatability

[Jeff-Grant]

Having received the DTP70, i have been measuring and comparing results. What I have found is that my old i1Pro in th IO has better repeatability. On a TC 918 target, the i1 combo gives me a delta e of about 0.5. The DTP is beter than that for most patches but consistently has one patch between 3 and 4 and a dozen or so above one. These patches are all dark ones. My understanding is that the DTP should be more consistent so I'm wondering what could be going on. Is this what happens to old spectros?

[Jeff-Grant]

Answering my own question, it would appear that the DTP 70 is sensitive to patch size. The 7mm default produces a lot less consistent result than a 9mm patch size. At 9mm, I get an average de of 0.07, with only one patch above 1, and at 1.15, I can live with it.

[Jeff-Grant]

I just tried a 9.5mm patch set. It just gets better. I now get an average DE of 0.09 with one patch of 0.72, and an average of 0.22 in the worst 10%. Th worst patch is the 0,0,0.

[Rhossydd]

That's an interesting observation and what you would generally expect. Having done a fair bit of testing on the DTP-70 myself, I'd say that increasing patch width improves reliability of measurement for the testing I've done.

Once you start looking at comparing very low dE values there are a lot of variables to consider.

Have the prints had time to fully dry out ? [4 days is a sensible minimum]
Have many times are you measuring each sheet ? [I used 5 sets of measurements, so 10 results to compare]
Does the accuracy of the spectro change with time powered up (heat) ? [possibly]

There are also significant differences between the reliability of reading different paper types and I'd say you can go further and you should assume that different printer models and resolutions will also give other issues with reliability of measurement.

Then a final consideration is does it actually matter when the  dE values are so low, especially the errors are measured in very dark values ?
Are the final prints made from the profiles built with such minor improvements in measurement accuracy any better ?

Is this what happens to old spectros?

I doubt it is much to do with the age of spectro, but more modern designs may be better at reading low values.

[Jeff-Grant]

Many thanks. That gives me more to ponder. My testing to date has been far more basic. I acquired the DTP 70 from a friend recently and wanted to test it for myself to find what worked best. It had only been used occasionally for a few years so it was a bit of a voyage of discovery. My first surprise that Colorport on El Cap just works. I know that Xrite has a lot to answer for but I was really pleased to find it still supported.

My testing was simple. I didn't bother with overnight drying, but did give it a couple of hours. I thought that two passes one after the other would do the trick. I started off with the default Colorport patch size of 7mm. That gave very good overall results with a couple of wild ones each time. I then started increasing patch size and watched the results getting closer. At 9.5mm it's close enough for me.

I agree that, at that low level, I should just build some profiles and start printing. I can't see a lot of point in multiple passes and averaging.

[Rhossydd]

I know that Xrite has a lot to answer for but I was really pleased to find it still supported.

To be pedantic, it works, no one will offer any support.

My testing was simple. I didn't bother with overnight drying, but did give it a couple of hours.

Depending on the printer/ink/paper, colours are unlikely to be stable enough for these sorts of measurements for at least 36 hours, sometimes even longer.

I thought that two passes one after the other would do the trick.

Try multiple passes, results WILL vary and that variation will change again with different factors like paper surface.
Once you've done some rigorous testing to establish the error level that's likely in your machine, move on and do some testing of how colours change when they dry, that's interesting.

I agree that, at that low level, I should just build some profiles and start printing. I can't see a lot of point in multiple passes and averaging.

The point of testing these sorts of issues is to find out when multiple passes and averaging might be advantageous. However there's little point testing unless you use sound methodology and understand all the issues that might effect your results.

[Jeff-Grant]

My best people are working on it.