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Author Topic: Expectations distinguishing gray levels  (Read 2446 times)

robest

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Expectations distinguishing gray levels
« on: February 28, 2012, 05:09:56 pm »

I've just started printing on Gold Fibre Silk with a iPF6100. Initially I used the stock Ilford profile (Semi-gloss photo media type) but I've now had a custom profile made (I don't have a profiler myself so I printed the targets and sent them off). On the recommendation of the canon wiki I used The Special 5 media type.

I printed a test image (from Outback Print) with both profiles and whilst the stock profile wasn't bad the custom profile was a definite improvement especially on the red and blue ramps (fixing an inversion and purple tint respectively), and the saturated reds of the second strawberry. However, one possible? negative was that with the stock profile I could distinguish down to gray level 4 and up to level 252, whereas with the custom one this reduced to level 6 to level 251. This is quite a minor change (I think) but I wanted to gauge what other people's expectations would be. I'm not sure whether the change is a limitation in the profiling or is due to the switch in media types. But before I go to the effort/expense of possibly re-profiling with different media types and/or running some printing tests I thought I'd ask on here. I'm printing quite a lot of high contrast B&W images at the moment, so maybe it does matter??

Thanks for any advice!
Rob
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Mark D Segal

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Re: Expectations distinguishing gray levels
« Reply #1 on: February 28, 2012, 05:17:38 pm »

It's really hard to pinpoint what the cause of a change is when more than one change occurs at a time. My guess would be that the media type has the more critical influence. Personally, I would not look upon a change from 4 to 6 as anything to be concerned about. It would be difficult to distinguish between those two levels on paper, and even if you could, there aren't many images where there's much to be distinguished between those levels of blackness.
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Mark D Segal (formerly MarkDS)
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robest

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Re: Expectations distinguishing gray levels
« Reply #2 on: February 28, 2012, 05:24:43 pm »

Yes, I realised that changing two variables was not ideal - just a shortcut really given I don't have a spectrometer and am a bit miserly with expensive paper.  ;)

But thanks for the reassurance - I'm just not experienced enough to have a feel for whether that slight change would actually be visible / something to worry about...
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Alan Goldhammer

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Re: Expectations distinguishing gray levels
« Reply #3 on: February 29, 2012, 09:33:34 am »

One other thing that may have happened is that the profiling service may not have included a grey scale as part of the target so you lost a little bit as you noticed.  When I profile for myself or others, I always include a set of B/W patches that addresses that issue.  On an Epson 3880 the Ilford stock profile is pretty bad and my profile was far superior in a number of ways.  I could distinguish down to 4 and up to 252 but as Mark says the profile you have is just fine.  It's really hard in an actual photo to detect any difference in those shades (unless of course you happen upon an actual grey scale ramp in nature ;D).
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Mark D Segal

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Re: Expectations distinguishing gray levels
« Reply #4 on: February 29, 2012, 10:18:05 am »

Alan - yes agreed, from my experience with the 3800, Ilford's profile for this paper is easy to improve upon. As for the tonal range of grey patches in the profiling target, I don't know of a professional-grade target that doesn't have them - maybe not laid out as a ramp, but definitely in the matrix to be calculated from.

One other point - depending on the quality of display one has and its profiling, it is possible to see on the display a subtle tonal difference between L4 and L6 (in the L*a*b* scale) - however this is much less likely to be as visible on paper, if at all.
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Mark D Segal (formerly MarkDS)
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MHMG

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Re: Expectations distinguishing gray levels
« Reply #5 on: March 14, 2012, 08:43:29 am »

sRGB and aRGB color space both use gamma 2.2 tone ramps which for RGB neutral values of 1,1,1 through 5,5,5, round to L*=1 while RGB values of 6,6,6 through 9,9,9 round to L*=2 in the CIELAB color model (note: RGB 0,0,0 = 0L*).  A difference between 1 and 2 L*  translates to delta E= 1.0 between the two gray ramps you generated in this deep shadow value. Delta E theory suggests the typical human observer can see delta E =1 increments as "just noticeable", ie. a very small visually discernible difference. At the high end for RGB = 251,251,251 versus 252,252,252, both sets round to L* = 99 (100L = pure diffuse white = RGB 256,256,256). Hence, I think as long as your new profile generates otherwise more well behaved tonal ramps and color fidelity over the full scale, your new custom profile is actually better overall. Even though it loses out in shadow detail by a very tiny amount, the amount is so small that you should have no trouble extracting good shadow detail with appropriate image edits when needed.

I have a monitor checker target that uses the step-off in the low L* values from 0 - 9 and also the highlight L* values 91-100 to help evaluate monitor calibration accuracy. I don't usually print this target since it was designed for verifying monitor performance. That said, if the gray ramps in this target look good on your monitor (ie. your monitor is well calibrated) then a print of this target using appropriate printer profile and Relcol/w BPC might be a good way for you to check how much highlight and shadow detail you are losing when printing straight through the profile with no additional corrections.

Here's the direct link to the MonitorChecker target: http://www.aardenburg-imaging.com/cgi-bin/mrk/_4448ZGxkLzBeMTAwMDAwMDAwMTIzNDU2Nzg5LyoxMDM=


cheers,
Mark
http://www.aardenburg-imaging.com
« Last Edit: March 14, 2012, 03:36:13 pm by MHMG »
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Alan Goldhammer

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Re: Expectations distinguishing gray levels
« Reply #6 on: March 14, 2012, 11:08:39 am »

Thanks Mark, this is quite useful.

Alan
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Geraldo Garcia

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Re: Expectations distinguishing gray levels
« Reply #7 on: March 15, 2012, 12:29:51 am »

Useful indeed!
Thanks Mark.
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