Yesterday, I managed to linearise my CRT monitor. I was not impressed by it, things looked awkward and the gamma value was way off the normal range. When I wrote my post yesterday, I went home thinking about an ageing triode: as I said before, the characteristics shift towards lower currents (luminance!), with some pretty bad non-linear distortion. So I plotted my measured gamma values against the driving signal. Bingo. Gamma was around 4 on 6% brightness and 2.5 at 96%. Whoa.

So I had to change the bias on the valve (monitor: increase brightness to around 80% from the factory-set 50), until I could perceive a 1% patch with respect to the black background. Yes, and I re-did all 300 of my measurements as well… this time it worked as expected: gamma varies from 2.3 to 2.8. A bit too hefty on the red, but I don’t need to worry about that, as I am now interested in luminance only.

Yes, I managed to linearise the monitor with both settings. However, there are moments when ‘things work, but they don’t feel right’, and this was one like that.

I assembled my experiment setup, and tested myself to obtain preliminary data. Well, I’m not blind :). But my vision surely doesn’t know how to solve an integral!

Today I implemented the data format, and calibrated the monitor (that is, three hundred individual measurements, by hand, the old-school way). Been away to see adapting boundary techniques as well.

The monitor is today’s wierd one: Normally, the triode gamma value should be around 2.5 for a CRT (1.1 for an LCD). This old fellow does 2.94. And not just that, it barely does 70% of its original spec in brightness.

If I remember right, the cathode ‘vanishes’ with age, and therefore the distance between the grid and cathode increases. This means that gradient (transconductance) of the valve decreases, so the nice x^2-like graph gets distorted. It took me 6 hours to make the measurement properly. Needed to be in complete and utter darkness, and had to read the photometer by hand.

It was fun, even made a notice on the lab door 🙂

The adaptive boundary setting will have to depend on the luminance level. Tomorrow, I will be able to get more data, and can see the emerging pattern. Need to plot dy/y.

The computer booted up today without any major hassle. I had display. I am impressed!

Finished the first version of tests. What caused the flicker wasn’t by Windows, it was Matlab writing to the console. By suppressing the messages, I managed to provide the appropriate stimulus (Thanks Jenny!).

The code works, it may be worthwhile cleaning up, as now they operate as functions that access pre-defined and pre-set global variables. For some reason, this is a major no-no in matlab. Probably because they don’t have nice mutexes implemented for variables, and because functions are there to make software workspace-independent (which I intend to do, but needs more integration!).

Both tests appear to be working now, interestingly I got some weird results. Of course the dispay is not calibrated yet, so anything could happen, the wackiest result is just as inaccurate as the most sensible one.

I couldn’t do much with the photometer (still couldn’t get oscilloscope probes), I have two options:

1., Do the calibration by hand, which is a lengthy, painful procedure.
2., Try to borrow (beg! :)) an other one, from an other lab, and try making a software to automate the calibration.

Buying an other one is not an option, as the cost is about 3000 pounds for a device that was designed in 1987.

Anyway, when calibration has finished I just need to surround the brightness/contrast/gain control buttons of the monitor with an electric fence and not to update the driver.

This day started as a problematic one: almost the whole day passed when I finally got my admin account for the computer. And that’s when the steamroller started!

When I am in a project, I make sub-units in order to achieve goals and measure progress. I think I have two out of three done. The three sub-units are the following:

1., Eyesight alignment and relaxing stimulus (95% done)

2., Brightness control for the patch (70% done)

3., Frame alternator

The fist one is practically ready. I am using a randomly organised, static binary starfield, which will give a reasonable overall brightness, and won’t set off the monitor to full blast, which is very unpleasant in a completely dark room.

The second one I struggled with: It seems that Windows and libusb doesn’t really mix: I managed to crash the entire OS (yes, not just matlab itself!) many times. And every crash caused a good 10 minutes downtime to allow booting. So, I re-mapped shade control to the following:

Absolute mouse Y coordinate (with respect to the screen resolution)
Sublte control is done with the left and right mouse keys. Quitting is done by pressing the scroll wheel.

Originally, scroll wheel + derivated mouse Y coordinated would have been the solution.

I am concerned about the performace: Will I have enough ‘horsepower’ to render four patches at 140 frames per second? I will have to check UI at every 4-5 frames only, so I can have some relief there.

Also, by declaring and setting variables before loops, I could save more computational time. We will see.

I have fiddled with the photometer as well: it doesn’t appear to behave how the protocol is described: it regulary sends garbage, which is randomly mixed with data. Not good. Will take a look at the outgoing signal with an oscilloscope. Last time I had this problem with and old kit was due to inadequate smoothing on the power rail. Also the poor thing wasn’t calibrated in two years!

Having been doing some recruitment recently, I thought I’d share these thoughts prompted by the experience.

1. Find out the name of the scientist you are applying to work with, and address your letter “Dear Dr Read” or whoever. If you just write “Dear Professor” or “Dear Sir/Madam”, I’ll know you haven’t bothered to look up the name of the PI recruiting, still less looked at my website, and your subsequent avowals of profound interest in my research will sound … unconvincing.

2. Don’t say anything that sounds like it has been cut and pasted. If you tell me “I am fascinated by your research”, I’ll know you just say that to all the PIs. Something like “I am fascinated by your work on computational modelling of the neuronal mechanisms underlying stereopsis” will flatter me much more effectively.

3. Similarly, rather than saying something generic like “I have read your publications with great interest”, it would be better to explain why you like a specific paper. It probably is a good idea to look through some key publications of your prospective PI before coming to interview; after all, you want to find out if they are any good or not. Definitely don’t claim on the cover letter to have read all my work with great interest, and then be unable to describe even a single paper at interview, not even at “the one about vertical disparity” level of detail.

4. Referees should be academic. Don’t bother to give me a referee’s contact details and describe them simply as “an old friend”.

5. Similarly, if you’re applying for a postdoc, I’m not too interested in your hobbies unless they are clearly relevant. If you do public speaking as a hobby, I’ll imagine you must have good oral communication skills. Foreign languages could be useful in networking at conferences. But I’m not too fussed whether you play the guitar or kayak. As a general rule, scientific PIs aren’t really bothered about whether you are a well-rounded individual with a life. If you are, great, but we mainly want to be sure you’ll produce data and write papers.

6. Newcastle University has a space on the online application form: “Please confirm how you meet the essential criteria as set out in the person specification for the position, and address any gaps. Please describe how, and to what extent, you meet the desirable criteria.” How it works is that I am going to sit down with a matrix and score every applicant for the essential and desirable criteria. This is your opportunity to help me out. Yes, I can probably infer stuff from your CV, but I may miss something. So help me out and tell me how you meet the relevant criteria. I understand it’s time-consuming, but if you really want the job I think it’s worth it.

7. In general I’m a big fan of the “nothing ventured nothing gained” approach to life, but you can overdo this. If I’m advertising for a postdoctoral research assistant, have listed “science PhD” as essential, and you have neither already got a PhD nor are working on one, then it’s a waste of both our time for you to apply. If you think you have some special skills which might make me consider you anyway, drop me an email to ask before applying formally.