gallois wrote:
Many B+W films are not red sensitive
Stuff from 100 years ago yes, but most film stock for a camera is panchromatic.
Using what is call Hald CLUT (colour look up table) I took one of the ishari plates and simulated two b&w films, I intentionally did it at low resolution as seeing the image smaller makes it easier to see the numbers…
The original
A simulation of an orthochromatic film (no red, sort of thing used in the pre world war 2)
Next is kodak tri-x modern panchromatic film made famous from about the 1960’s I think 
finally a infrared film b&w film that was typically used aerial photographic applications
keep in mind this just a simulation, using real film, and real a ishihara plate correctly exposed to daylight, would likely get a subtlety different result.
At least for myself I can see number 74 when simulating a panchromatic black and white film (tri-x).
gallois wrote:
Many B+W films are not red sensitive which is why red lights tend to be used in B+W processing and printing.
That is not true: Except for some special films, B&W fils have actually been quite sensitive to red light – many of them even much more than the human Eye into the infrared spectrum so that there has been an easy way to do IR pictures by just using filters that block the visible spectrum. (With those filters the Viewfinder image was dark to the human eye but after processing the film you could see the image.
What is true is that many B&W papers used for making the prints from the negative have been not sensitive for red light so that you could use red light while creating the prints (but only after the film has been processed).
Peter wrote:
So, how do you fail Isihara, but pass a lantern test 100% ?
Because they test slightly different thing.
Laterns are actually very badly to not at all suitable as general test for color blindness (or to be more precise: color vision impairment). This is not what they are designed for. Their purpose is to check if color vision is good enough for a very specific task. That is also the reason why there are so many different lantern tests around – it is not, that different manufacturers had their own test but rather that they have been designed for specific tasks. To check if a train driver can differentiate between the green, red and yellow signals, there has been a lantern with exactly these colors (and different lanterns in Germany, UK, US as the colors of the signals have been different). You could be completely Blue/Yellow blind (tritanoptic) and still pass the train driver lantern test with ease as there simply is no reason to use a blue light in this test.
So Ishihara tells you if you have any color vision impairment. A lantern test tells you if your impairment is relevant for a specific task.
And there is btw. a major discussion which lantern tests are still adequate for flying. E.g. the Farnsworth test (FALANT) originally developed for the Navy has been regarded adequate also for aviation for quite a long time. It does, however, only test for the three colors red, green and (orange)yellow. That has obviously been enough also in aviation for a long time when the only signals one had to differentiate have been the green and red position lights or signals from the tower. With modern avionics more and more information is also coded in other colors and therefore one could argue that a 3 color test is no longer suitable.
I hate to disagree but I am not quite 100 years old yet and I remember using B+W film from Ilford in the 1950’s
But it is correct that most modern panchromatic films are red sensitive.
Well done Ted for doing the experiment. I am pretty sure that the result is reasonably accurate. Other colours will of course give different results.
So is it really a good CV test or something that triggers an AME to run further tests.
So the next question is could you pass the Ishihara (if you did have CV problems) by squinting/screwing your eyes up until nearly closed?
Once you look at this, start with the older one, you will look at “color vision” completely differently forever
Updated (also the guy)….
We cannot see color, it does not exist as such… we simulatecolor based on past experience.
gallois wrote:
So the next question is could you pass the Ishihara (if you did have CV problems) by squinting/screwing your eyes up until nearly closed?
That is exactly one of the reason why Ishihara uses this “funny” dot picture and not just a number in one color on a background in a different color. By just squinting your Eyes it gets closer to B&W but the visual resolution is also reduced so that you can no longer see the circles and hence identify the numbers.
It has been said before: If you really want to it is not so difficult to cheat Ishihara. If you are not completely color blind you might not be able to read the numbers, but looking at them carefully you will notice that not all plates look the same to you. Hence you can memorize the plates in a way like “The one where the big circle at 9 o’clock position is a bit lighter than the middle sized circle next to it is the 74.”
The only thing you need for doing so is a friend who does the test before you at the same physician to check which manufacturers cards they use (because in that sense the different card sets look differently).
It doesn’t surprise me that how we see colours is based on learning over the years. There is no “objective reference colour”; there cannot be because you can’t see inside somebody’s head.
And as the above videos show, we auto correct continually anyway so e.g. white paper looks white to us under almost any light, but every photographer knows the sky makes everything blue Different kinds of blue depending on the cloud cover, the sun, etc. I do manual white balance (in lightroom) on all flying photos, especially mountains, otherwise they look crap, especially with snow cover.
What does the Isihara measure? Bollox IMHO. As Pape (link posted earlier) demonstrates, CV is not needed for safe flight. And on a PFD, you need to clearly distinguish blue from brown The rest is just text and lines; could be monochrome.
Peter wrote:
What does the Isihara measure? Bollox IMHO
The eye is a receptor of light over a certain frequency band. Color is detected using 3 distinct cells tuned to a certain narrow frequencies. Obviously if one or more of those cells are lacking, then this receptor will have difficulties detecting and differentiating between certain colors compared with a normal eye. This is exactly what the Ishara test measures. If this really matter at all vs flying is another matter entirely. How the brain works is irrelevant IMO. If the eye cannot detect certain frequencies of light, then the brain has no clue either.
If two persons with identical eyes perceive color differently, then this is merely semantics IMO, like different languages, or perhaps similar to taste. If you are brought up on “meat and potatoes” exclusively, then fish tastes like shit Taste can be trained and so can vision. With patience anyone can acquire the exquisite taste for Rakfisk and Surströmming for instance (fermented and uncooked fish) But training your brain will not help all that much if your tongue cannot differentiate between salt and bitter to start with. Then I guess everything tastes like chicken
The problem is that this is a circular definition.
The Isihara plates do not test colour vision. They test the ability to identify a human-recognisable (i.e. totally subjective) pattern: a numeric character, constructed of dots of colours deliberately designed to be confusing. No real-world challenge is like that! This is what Pape (link above) challenged, successfully.
Real-world challenges are completely different, and much easier.
The altitude and speed tapes on a “EFIS” presentation are not made up of these stupid dots. A totally monochrome person (of which there are extremely few) can use an EFIS perfectly.
If there were indicator lamps which are red or green in the same lamp position then a completely monochrome viewer could not distinguish them. But this is never done in aircraft panels – AFAIK. It is a bit impractical with lamps, although easy with LEDs.
Peter wrote:
The Isihara plates do not test colour vision. They test the ability to identify a human-recognisable (i.e. totally subjective) pattern: a numeric character, constructed of dots of colours deliberately designed to be confusing. No real-world challenge is like that! This is what Pape (link above) challenged, successfully.
The ability to recognise these patterns depends on having normal colour vision. (And being able to read, but that’s taken for granted in our society.) You are of course right that in the real world you get other cues that can substitute for defective colour vision (like the arrangement of lights on traffic signals or EFIS symbols). But that doesn’t mean that “the Isihara plates do not test colour vision.”
They test CV allright but in a manner which is wholly tangential to the intended application.
So basically completely useless as a CV test for a pilot.
Accordingly, one could probably devise a test which depicts an EFIS display, with fake colours, which a pilot fails. That would also be “testing CV”
So much of aviation medicine is crazy.
