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Author Topic: Slight magenta cast on Canson Baryta Prestige - Canon Pro 4000  (Read 3389 times)

Mark D Segal

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Re: Slight magenta cast on Canson Baryta Prestige - Canon Pro 4000
« Reply #40 on: April 15, 2018, 04:28:00 PM »

Yes, than i1Pro which is 100; which is the OP using?

In the opening post OP says i1Pro2.
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Mark D Segal (formerly MarkDS)
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Mark D Segal

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Re: Slight magenta cast on Canson Baryta Prestige - Canon Pro 4000
« Reply #41 on: April 15, 2018, 04:34:47 PM »

One difference the I1P and I1Pro 2 have over the older I1Pro is that chart scanning is done with quadrature position sensing on the underside of the Spectro. The earlier one looked for contrast differences between adjacent patches because it didn't have the quadrature position info. The contrast info that matters is the white/black bars at each row end. This establishes the patch locations using the quadrature info. If it's anything like the iSis, it heavily weights middle samples that are 2 mm from the actual patch edges. This is actually testable and I've done that for the iSis. Might be interesting to do for the I1Pro 2.

If you checked it, would the answer inform the profiling process in any particular way? The only choices we have in regard to the scanning procedure are whether to scramble the patches and how slowly to scan them. Safest and most reliable option set is to scramble (even if not strictly necessary) and scan slower rather than faster. Typically with about 30 patches per row, if you think 100 samples + per patch is enough for good averaging (smothering outliers), spending about 20 seconds on a row would seem to do it appropriately. The larger the number of total samples per patch in theory the less important any weighting would be - do you think?
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Mark D Segal (formerly MarkDS)
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Doug Gray

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Re: Slight magenta cast on Canson Baryta Prestige - Canon Pro 4000
« Reply #42 on: April 15, 2018, 05:11:30 PM »

If you checked it, would the answer inform the profiling process in any particular way? The only choices we have in regard to the scanning procedure are whether to scramble the patches and how slowly to scan them. Safest and most reliable option set is to scramble (even if not strictly necessary) and scan slower rather than faster. Typically with about 30 patches per row, if you think 100 samples + per patch is enough for good averaging (smothering outliers), spending about 20 seconds on a row would seem to do it appropriately. The larger the number of total samples per patch in theory the less important any weighting would be - do you think?

The main advantage to the quadrature positioning info is that you don't have to be as careful to smoothly move the spectro across the patches. You can even briefly stop mid row without a problem. A secondary advantage is that the patches don't have to provide patch to patch contrast changes which is required by the older I1Pro.

I generally did a fairly  fast row scan with the I1Pro 2 of around 4 seconds. 2 seconds was too short.

The iSis doesn't use quadrature but rather a stepper motor with better precision. It also does not use adjacent patch contrast at all so one can layout patches any way desired.

I almost always scramble patches. It doesn't seem to affect the 9800 one way or the other but it does produce slightly worse profiles on my 9500II.
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Mark D Segal

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Re: Slight magenta cast on Canson Baryta Prestige - Canon Pro 4000
« Reply #43 on: April 15, 2018, 05:21:01 PM »

For positioning I can see that, but I was asking about the importance of knowing whether the spectro centre-weights the measurements - which I wonder whether an i1Pro 2 does. It knows where it is by virtue of the striped grid it is reading as it moves along and the patch it is reading in real time; its reading is timed as so many samples per second; to centre-weight the samples in time it would have to do complex calculations with instant feedback tracking the varying speed that the user deploys reading a row. Seems improbable. The iSis is a different animal - fixed and known speed so fewer variables in real time. 
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Mark D Segal (formerly MarkDS)
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Doug Gray

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Re: Slight magenta cast on Canson Baryta Prestige - Canon Pro 4000
« Reply #44 on: April 15, 2018, 06:35:39 PM »

For positioning I can see that, but I was asking about the importance of knowing whether the spectro centre-weights the measurements - which I wonder whether an i1Pro 2 does. It knows where it is by virtue of the striped grid it is reading as it moves along and the patch it is reading in real time; its reading is timed as so many samples per second; to centre-weight the samples in time it would have to do complex calculations with instant feedback tracking the varying speed that the user deploys reading a row. Seems improbable. The iSis is a different animal - fixed and known speed so fewer variables in real time.

Yes, the iSis does have those advantages. The I1Pro2 would have to window it's samples, excluding those where the 4mm aperture has potential for overlapping two patches plus accounting for error. A design approach would be quite straightforward. Include all samples in the window, add them, then divide by the number of samples in that window. It may, or may not, include some sort of window rolloff like the iSis which uses a Gaussian window giving the most weight to readings within 1mm of the patch center. I would think that part of the program code could be quite similar. The only reason I can think of for not using a rectangular window is that if registration errors occurred or the paper dried with a slightly uneven shrinkage then a Gaussian window would reduce those errors.

But there is a tradeoff. The Gaussian window images a narrower part of the patch and so paper irregularities are more likely to show up. It also increases the noise (less photons) but that effect is miniscule. The illuminant is so intense that the shot noise is vanishingly small when measuring reflectance spectra.
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Nickilford

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Re: Slight magenta cast on Canson Baryta Prestige - Canon Pro 4000
« Reply #45 on: April 17, 2018, 12:33:25 PM »

Thanks to all who have helped with this topic, I have managed to come up with a satisfactory result with the Canson Prestige and have learned quite a bit in this thread alone. Some of the info left by more seasoned users is going to take me a while to digest but will get around to it with a little more time.

Once again thanks a lot!
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Mark D Segal

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Re: Slight magenta cast on Canson Baryta Prestige - Canon Pro 4000
« Reply #46 on: April 17, 2018, 12:54:54 PM »

You are welcome. I'd be curious to know what you did, in the final analysis, to come up with a successful result. Would be interesting, given the variety of opinions and suggestions in this thread.
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Mark D Segal (formerly MarkDS)
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Nickilford

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Re: Slight magenta cast on Canson Baryta Prestige - Canon Pro 4000
« Reply #47 on: April 18, 2018, 01:03:37 PM »

You are welcome. I'd be curious to know what you did, in the final analysis, to come up with a successful result. Would be interesting, given the variety of opinions and suggestions in this thread.

For the most part I followed your advice Mark. I had a go trying the linear target route after I thought the scrambled target didn't improve all that much. But then ended up settling with the scrambled 2371 patch target. Also found better results with ACPU rather than PSP (Print Studio Pro) I would still say that I am not "as satisfied" with the Prestige profile as I am with all my other papers (Canson or not) but still feel pretty good with the prints. It seems I was thrown off a bit by the increased saturation with the prints on Prestige, probably mistaking the more intense colours with a colour shift instead. I'm really picky and can (un)fortunately pick up even the slightest colour shift.

Here was what I used:

target printed from ACPU (Adobe Color Printer Utility), didn't like the results when printed from PSP
2371 scrambled patch layout
target read speed about 5 sec/row (will decrease the speed in the future)
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Mark D Segal

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Re: Slight magenta cast on Canson Baryta Prestige - Canon Pro 4000
« Reply #48 on: April 18, 2018, 01:09:34 PM »

Thanks for the info. Interesting that you derived better results from using ACPU rather than PSP on the Pro-4000. But it is what it is.......whatever works best.
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Mark D Segal (formerly MarkDS)
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