X-Rite i1iO and a B&W test image
X-Rite i1iO and a B&W test image
Measuring black and white print linearity
Some time ago Keith reviewed the i1iO scanning table, for automating the measurement of printer profiling targets.
Our original iO has just been updated to work with the current i1Pro 2 spectrophotometer, and with i1Profiler software.
We’ll have a review of the new iO in due course, but Keith has been looking at using the iO to both speed up and increase the accuracy of measurements from his popular black and white test image.
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The i1iO table is available from B&H | Adorama
A new version of the test image is available along with the i1Profiler target files.
The step target is used as part of Keith’s testing process during for his printer reviews, such as the Canon PRO-2000 seen in some of the photos below.
The targets are often used to build QTR linearising profiles, there is more about the (non automated) process at:
Adapting the test image for the iO
I’ve used my standard test image, but with the greyscale ramp changed from one for manual measurement with ColorPort software, to one that works with i1Profiler.
- Just in case the i1iO is a bit excessive for your needs, remember that the original (V2) version of the test image just needs a basic spectrophotometer. There are also test charts for the ColorMunki and SpyderPrint.
All the various parts of the image are explained in the main article about it.
I’m printing the image from within Photoshop, using the Printer’s B&W print mode.
There are sections covering this in almost all my printer reviews.
The print is printed on a sheet of A3 paper, from a box of Innova IFA-59. A bright ‘glazed’ glossy paper I tested a while ago (IFA-58,59 review)
You can see some of the other (colour) target types I was testing for a more detailed i1iO review.
The iO robot arm
The iO has been updated with a new mechanism that holds both the original i1Pro and the newer i1Pro2
Here it is with our fleet of i1Pro spectrophotometers
Our eye one iO was an original test version from GretagMacbeth – this has had a major overhaul by X-Rite and is now effectively the current (2016) version with the exception of colour scheme and decals…
The sheet can run off beyond the measuring area – it’s just the target we’re interested in.
The table has an electrostatic hold, which easily keeps the paper in place.
Using the iO with i1Profiler
The updated test image download includes a patch information file that you can load, as part of the ‘Measure Reference Chart’ function.
i1Profiler offers measurement options like I’m using here, even in its ‘demo’ (unlicensed) mode. For full profiling though, you need an appropriate license for the software.
Note that even if you’re using an RGB printer (such as the PRO-2000) you need to load the target in CMYK mode (the chart is a single set of ‘K’ values).
As you can see, it’s a simple 51 step grey ramp, going in 2% steps from paper white, to full black.
The test image is supplied in the Grey Gamma 2.2 colour space, to make it more like printing a B&W photo, which might well be in a gamma 2.2 space (such as Adobe98) anyway. If you need to change things, the download comes with a 16 bit TIFF version.
Since I’m using the newer i1Pro 2 device, I have the choice of M0,M1 or M2 measurement types (of which more later).
Spot reading is slower, but gives me the chance to average multiple readings for each patch (I’ve set it to 3).
The iO needs to be told where the chart is positioned (it’s not -that- smart).
You need to move its sighting aid over three corners of the target.
Then down
Here’s a view of the crosshairs, from when I was testing a colour target
Finally over to the opposite corner.
At this point the software asks if you wish to proceed.
The i1iO arm still impresses me as much as when I first got it ;-)
The progress of measurements is shown.
After some five minutes (remember I’ve set it to average readings, which slows things down a bit), I can save a data file from the measurements.
If I’m using QuadToneRIP software, then simple LAB values are all I need.
I include paper info. and settings in the name (highest quality with CO coating set to Auto).
The measurements
After dropping the data files (one each for M0,M1 and M2) on to the QTR RGB icc profile application, I get the following graphs (and linearising ICC profiles).
The paper is a bright one with some optical brightener (OBA).
M0 – some UV.
M1 – Approximately D50 (known amount of UV)
See how the ‘b’ curve is further to the right, until blacks are above 70%
Finally M2 – what is also known as ‘UV Cut’
Comparing charts, you can see how the OBA was contributing to the readings right up to ~90% black.
Before getting too worried about the different measurement modes, note the very similar ‘L’ curves.
The main ways I make use of this information is to decide whether, for a particular printer/paper/ink combination I need to linearise my print output before printing. See the articles about making the curves for more about this.
Suffice to say, that the B&W print modes of the larger Epson and Canon printers I’ve looked at of late show a general improvement in linearity, such that I’ll often not use any correction profiles I’ve made.
The OBA differences here suggest that the prints will look somewhat different in daylight and tungsten lighting. I deliberately chose this bright and heavy glossy paper for some other testing connected with the Canon PRO-2000. It works well for some photos (colour and B&W) but I’m not generally a fan of high gloss.
Colour tints in B&W prints under some lighting is a recurring problem, which I’ve looked at in more detail:
X-Rite have a PDF that discusses some aspects of the measurement modes.
A couple of diagrams from the document show the differences quite well.
First, three measured curves from a non OBA paper, such as one of the cotton rag papers I like for many of my B&W photos
Secondly, the difference that a lot of OBA makes
Conclusions
The i1iO table lets me quickly measure embedded test charts within a larger image.
In terms of convenience, it also saves me cutting sheets of paper to make the measurement manually.
In terms of accuracy, it allows me to average up to 5 sets of measurements for each patch – I could have done this by manually measuring the target five times, but let’s be realistic, I’d never get round to it…
The i1iO table is available from B&H | Adorama
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For information about other printers, paper reviews and profiling (colour management) see the Printing section of the main Articles and Reviews page, or use the search box at the top of any page. There are also specific index pages for any articles connected with the following topics:
- Digital Black and White
- Tutorials and 'How to' articles
- Colour Management
- Printer test images
- Why do your prints look wrong?
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