CurtPalme.com Home Theater Forum

[perisoft]

OK, gentlemen...

A thread popped up the other day discussing MTF detection using MS Paint.

Those of you who know me (at all) will know that I can't leave well enough alone; my first thought was, "I can automate that". My second thought was, "I can use that to focus my projector if I hook up a web cam or other video device and can provide realtime feedback."

So, first, I fired up a web cam, pointed it at a test pattern, and focused away. Hot damn! Projecting a hugely blown-up picture of the web cam output allowed me to adjust optical focus far better than I'd been able to before; so-encouraged, I decided to try doing the same thing with astig.

I'd had a hell of a time getting astig anywhere near reasonable on my red tube; seeing a huge version on-screen made a massive difference. It's nowhere near perfect, but far, far better than before.

The next thing, I figured, was to be able to do this without eyeballing it. First, if you're adjusting focus and astig, the focus of the window you're watching to do the adjustment gets messed with. You could mitigate this by using a separate screen for the webcam, but that can be tricky; your only other option is to use a laptop and try to put it somewhere that you can see easily while your hand is stuck inside your projector.

Given that, the obvious task is to find a way to look at the pixel readings directly.

So, I fired up mah Visual Basic and had at it. I now have a nifty app that lets you set two pixel positions and (will soon) tell you the RGB values of each one, plus, probably, the ratio between the two. It'll read anything on the desktop; the trick is that if your webcam display uses an overlay my app can't get the pixel colors. I actually haven't tested mine yet.

But, the nice thing about this method is that it lets you use any optical device to do your work. If you wanted, you could use a DSLR with a macro lens, and write a script to auto-display new images; set your crosshairs anywhere on the desktop and fire away. Not as much realtime feedback as a webcam but potentially better quality.

Back to feature creep.

Originally I'd intended this to be just a personal thing, but since I can't leave well enough alone, I started making the thing slicker and slicker, so now I figure maybe other people might want to try it out too. I thought I'd ping the forum before I go doing file menus and installers and all of that crap, though.

Second, regarding feature creep, I'm looking at directly-integrating webcam support and adding in an astig helper - say, you'd pick a point and it would sample 8 points around it. You could use the result to see how round your pattern is.

One of the holy grails for me would be some way to help with optical corner focus; scheimpflug has always been a bastard for me. Only catch? You need four webcams, or a really OBSCENELY high-resolution DSLR!

Any thoughts? Anything you guys think would be helpful? Am I just insane?

[Nashou66]

Sounds cool. And yes shiempflug is the worst, and moving the Camera for each corner would suck.

Id try it, I think my external iSight might even work on my Laptop while running windows since it runs the built in one.

How will it select which web cam to use? And would you be able to support the iSight? It think there is a driver set for windows out there somewhere.

PS, Were all Crazy Peri, were CRT'rs

Athanasios

[perisoft]

[David_Web]

You could use Roborealm http://www.roborealm.com/
It supports VB directly so you probably feel right at home.

Stacking average or any other filter is easy.
Think there is a histogram as well which would be useful.

[garyfritz]

[perisoft]

[tse]

Cool. You can absolutely do this. Your idea of looking at eight points around a spot to determine how round it is sounds great.

To do scheimpflug I think will take four cameras (or a real high res one, like you said). One looks at the top center, one at the left side at the center, yada yada. Focus is easily seen if you project a test pattern of alternating black and white lines. Look at the light profile and compare white level to black level. Best focus is when there is the greatest difference between the two. Adjust the side to side control so left and right patterns "peak" at the same setting. Same with the top and bottom. It is right when you adjust the lens and all four camera displays peak at the same lens setting.

Maybe five cameras with one in the center. Adjust center focus barrel for best center focus then the outside barrel for the best outside focus.

Get the cameras up close to the screen so they are looking at a small area. Put a lens spacer between lens and cam so it can focus up close.

It helps alot to have full horizontal size and full vertical size projected when you do this.

Go for it. This would be a great tool.


Scott

[dturco]

If you make it easy enough to use I'm in for it. Heck, I'll help you beta test it. If I can do it, well... you know, anyone can.

Oh, I think the cheap four camera option is best/cheapest, since I don't have a DSLR camera

[Nashou66]

[perisoft]

OK, here we go:



Current features:

• Catchy name
• Always-on-top crosshairs; you can move the image or use GUI elements in the webcam without losing your place
• Crosshair visibility selectable
• Huge-ass MTF readout that assumes you'll be showing Focus!Focus! on your projector and it'll get fuzzy when you change the focus
• Set test points with keyboard so the window doesn't switch as soon as you click
• '1' and '2' labels automatically swap to the position furthest away from each other so they don't obscure the selected pixel

Obvious to-do:

• Complex, overwrought splash screen
• Installer with onerous but probably unenforceable EULA
• Zoom window with internal crosshairs so you can see where the hell your cursor is
• Calculate MTF based on more than one pixel selectably
• Test on an actual webcam screen instead of a screenshot from somewhere on CurtPalme/forum

Not-so-obvious to-do:

• Auto-seek high or low luma pixels near the clicked area to avoid holding down the select key and dragging around until you see the highest/lowest luma value
• Use temporal averaging on selected pixel to avoid crazy-changing MTFs with flickering output
• Selectably-huge-ass MTF readout for different scenarios

...and then there's the Far More Complex stuff like astig support, internal support of webcams, etc...

Anyway, it's a start. If I can determine that it'll actually work on a real webcam, I'll prolly package it up and let you guys play with it.

[Spanky Ham]

Very interesting idea. Is there a big difference between webcams or are they all pretty much the same?

[Hdale85]

What about using HD web cams? Also what about things like those little X10 cams or something, they have some really cheap ones but they aren't the highest of resolution.

[tse]

[perisoft]

The limiting factor with webcams isn't resolution but color depth and post-processing. They're designed to show people 3' away and the software does everything it can to look good in that scenario.

Anything that has no option to turn off auto contrast or gain will be essentially unusable. I was just lucky that this logitech let me manually set gain/contrast.

If I can pull in data via windows maybe that'll give me the 'raw'(ish) sensor data, or maybe the wdm will suck the data through the webcam's software. Time will tell.

[ecrabb]

Feature Creep
apologies to Radiohead

When I was up the night before,
Couldn't focus on the screen
It's such an enigma,
The MTF makes me cry

You help with the sharpness
On a beautiful screen
I wish I was focused
You're so f*ck***' focused

But I'm feature creep,
I'm the solution
What the hell am I solvin' here?
I won't just stop here

SC

[perisoft]

[David_Web]

That sucks. Had no idea that roborealm turned into a pay app. Used to be free.


btw don't go for an installer, make it portable!
Anything else is just stupid these days.

[Ampro at home]

Menard's has a 3 Megapixel webcam for 5 dollars and 95 cents this week. If the computer has enough USB ports it'd be under $25 to buy the cams. You might need a port expander otherwise which increases the cost slightly.

Mike

[garyfritz]

FWIW $6 for a webcam is not that unusual. Google shopping shows 5Mpix cameras for $6. Of course you'll probably have to pay shipping, unless you wrap it in with a larger Amazon order for free shipping...

[perisoft]

As I just mentioned in another thread - I grabbed an app called YawCam (http://www.yawcam.com/) that snags webcams directly. It should work perfectly for the MTF detector.