Compact Canon CDHK RAW & Lens Distortion

[chadfx]

I don't think this specific question has been answered before, apologies if it's been covered already.

If I am using CDHK with a Canon compact camera (A3300 IS) and shoot in DNG raw, it does not automatically correct for the lens distortion...so it appears different from the JPGs coming out of the camera. With most cameras this is the expected behavior, aside from some cameras that bake in the distortion correction into their RAWs as well.

Will Photoscan still calibrate correctly for these DNG versions from this camera? I would assume that I would not want to apply any distortion correction in another program before sending it to Photoscan, right?

I know Photoscan should normally handle this as expected, I just wasn't sure in this case, since this camera normally can't shoot RAW.

I'm attaching jpg/dng versions at 28 and 51mm to show the difference between the two versions. Thanks for any info. I imagine it will probably be fairly obvious when I test it out anyway.

-Chad

[chadfx]

In case anyone was wondering, the DNG RAW files from the little Canon A3300 w/CDHK kit worked out just fine. The images are MUCH cleaner than the highest quality JPGs the camera spits out. There's still some noise and other issues that go with small/cheap cameras like this, but it certainly is a way to put together a poor man's Infinite Realities. ;-)

This was a quick test with eight of them synced together with a hand built USB trigger.

http://sketchfab.com/show/cAaq3BTHjX26MCZvJijJwyKsjTS

[chrisd]

That is excellent!

I've been wanting to do something like this myself ...

What did you use for a rig to hold the cameras?


Chris

[chadfx]

Hi Chris,

I used a bit of a hacked together rig, since I've been also testing a multicam setup for other uses and didn't want to set up something permanent just yet. I'm also still trying to find a layout which will help me get the most out of the 8 cameras. I'm using a couple of light stands with super clamps holding two strong flexible arms horizontally. Then each camera is mounted to that with a smaller clamp with a mini ball head, so it makes it relatively easy to move the cameras around in orient them in whatever direction/layout is needed. With all of it on flexible arms, I can expand or contract the arc of cameras as well if I am close or far away from the subject.

The main problems I am running into are trying to get a good build of the geometry under the jaw and near the ears, which are both not seen by as many cameras. So in this rig I placed one camera much lower, which seems to help a bit. I will likely try to get the outer cameras a farther out to the sides next time. I've also been experimenting with different focal lengths and distances from camera. But it all takes time to test out and I haven't figured out how to squeeze more hours out of my day. ;-)

I hope this helps a bit. I can send links to specific pieces of equipment if you are interested. There are some brands sold here in the US (eg. Cowboy Studio) which are sold on Amazon or other online sites that generally have a lot of equipment which mimic the more expensive brands (Manfrotto, etc). It is a bit of a 'you get what you pay for' thing, where they are not as durable or well made; but for some uses (like these small/lightweight cameras) they can save quite a bit of cost.

Here's a pic of a similar camera setup (the two end cameras are usually oriented vertically like the others, not as shown here)  and also the camera/geom solve in PS (for those of you curious about the build quality).

Cheers, -Chad

[jerry]

cool, any new scans? how have you made the camera sync?s?

[chadfx]

nothing new just yet...I still want to try expanding the spread of the cameras a bit to get better coverage near the sides of the face. a more even lighting spread also might help. I'll be sure to post better results if I get them.

the cameras are synced well via a USB trigger I built that has a simple button switch connected to all 8 USB ports of the cameras and controlled via the CDHK firmware kit. there is a bit of a delay/lag while they all acquire focus/metering, but once they are all ready/locked, they seem to fire off at about the same time when I release the button. I haven't really tested it with a moving subject, and I have a feeling the sync is not exact enough to pull off something like that. there are sync delay adjustments in the CDHK remote controls, so maybe they can be dialed in fairly close.

[EMULAT3D]

Hey Chad,

Very cool setup! We are actually using the Canon A1400's in our camera rig, but haven't tried the DNG format due to the lens distortion. Have you found that Photoscan works around it nicely? Or do you tend to just do full zoom to reduce the effect?

Thanks!

[chadfx]

Hey Emulat3d, I've been converting the DNGs with ACR in Adobe Bridge and it seems to leave the lens distortion in the resulting converted JPGs (as I mention at the top of the post). I never got an official answer if this was a good or a bad thing. ;-)

But I can tell you that PS doesn't seem to mind these DNG-JPGs at all...as it seems to still align the cameras and build the geom without problems. The images certainly have much more image detail than the JPGs coming straight out of the camera. One thing to note is that the cameras are VERY slow to write out the DNGs (2-3secs)...so be patient when you're shooting. =)

It would be great if you gave it a try to see if it works in your situation as well. Good luck!

-Chad

[andy_s]

Hi Chad - apologies if you have already commented about this somewhere else [since it's the weekend i'm even lazier than usual to check the record] .

I do remember briefly looking at reyalp's 'alternative ptp client' topic on chdk a few months ago but hadn't really figured out how to trigger multi cams [via usb] and also transfer images using [another switch ?] the same usb connections before I was distracted.

http://chdk.setepontos.com/index.php?topic=6231.0

Any experience you might share ?

PS: to clarify, I think I had worked out how to trigger multi-cams but not how to transfer images [if possible] using the same usb network...

[chadfx]

Hi Andy,

I haven't really explored the alternative CDHK variants out there, but I see exactly why you'd love to have a trigger & transfer USB option. Sort of a cheap Breeze remote system?

Have you looked into SDM? I've seen some chatter about it in the past, and it seems it might have more sophisticated options than what CDHK provides. I think it might do what you want...but I'm not sure how well they are keeping it updated for newer cameras...the web pages appear circa 1998. ;-)

http://www.achillies.com/SDM/Docs/
http://www.achillies.com/SDM/Docs/eng/sdm/upload.htm

I probably would be inclined to explore this option eventually. Right now I'm manually copying images off the cards the old fashioned way...pull card out of camera, stick in computer, copy, eject....repeat x 8  (ugh!)

Please keep us posted on your progress!  -C

[chadfx]

and it looks like there might be some of this functionality directly (or a close spinoff) in the CDHK kit:

http://chdk.wikia.com/wiki/PtpCamGui

seems to be a bit less techy to implement at least.

[andy_s]

Thanks for this Chad.

I just reviewed where I had been trying to go with CHDK - that now a few months ago. It was really to try and develop a very large mixed point&shoot / DSLR system.

While I got some level of understanding I got sidetracked and now [just after having read my post on the chdk forum] can't even remember what some of my own post meant 

However, if we keep it simply focused on a total point&shoot / CHDK solution I wonder if [within a powered USB hub network] a first switch [say SWITCH1] could be inserted in the final USB connection to the computer and a second switch [SWITCH2] be inserted in between mains supply and the USB hubs.

CHDK Shutter Operation would then require: 

(i) initial conditions - SWITCH1  and SWITCH2 OPEN
(ii) CLOSE SWITCH2
(iii) Wait a second [or so] for all camera's LED lights to say they're ready to shoot
(iii) OPEN SWITCH2 [i.e capture the images]

What I don't understand is whether large propogation time delays are created throughout a USB hub network via hub transfomers etc

(iv) CLOSE SWITCH1 and SWITCH2...use reyalp's alternative ptp client to transfer the images [but since that's a 40 page 392 post topic i'm sure there's a few things to be aware of  ]

I got involved at post #12 here but quickly got distracted and left it in mid-air...

http://chdk.setepontos.com/index.php?topic=9420.0 

And as a ref:

http://www.flickr.com/groups/stereo/discuss/72157603947882001/

"The way it [SDM] works is that the camera loads software from the card that adds some new camera menus and controls. one of which is a "sync mode." When this mode is activated, it enters a loop that constantly checks for a voltage on the USB port. When you press and hold the momentary contact switch, it's wired to just deliver power from the battery to the USB's regular power and ground pins. When the software in each camera detects that voltage, it executes the camera's built-in programs to focus, set preflash, etc., and then it executes another loop that just keeps checking for the power to drop. When it detects the power drop, it triggers the final firing sequence. So, you just press the button, wait a second or so for both camera's LED lights to say they're ready to shoot, and release the button to fire both cameras. The sync is very good because that "tight" loop means both cameras detect the voltage drop at very close to the same time, and the firing process after that is fairly "deterministic" (not subject to a lot of randomness), so it happens in both cameras very nearly simultaneously."
 

[EMULAT3D]

Hey Guys,

What we did was create a trigger that would just simply interrupt the power supply on a standard usb hub. This way any cameras plugged in to the hub would be triggered simultaneously by the push of the switch. By default the hub is off until the button is pressed.

Then to pull the images off (still a pain and not ideal) we would just disable remote trigger on the cameras, then connect the hub to the PC to retrieve images (via Windows Picture Import). This is nice because you can then tag the images to a specific camera number.

Hope this helps!

[andy_s]

Thanks for the info EMULAT3D !

[chadfx]

Andy, the description from that flickr group post about SDM sounds exactly the way the CDHK switch works as well. The sync varies a bit while all the cameras acquire focus, etc...and then they wait for the voltage drop from the trigger and they stay fairly close in sync.

Emulat3d's solution to switch the power on a USB hub as the trigger (brilliant!) I 'think' should work fine with the basic CDHK remote software as well. Looks like I might have to give this a try!