Can I use Multiple DSLR cameras with my LCD application

[NA_Skins]

Hello, 

I am new with vision systems so please be patient with my questions.  We are trying to introduce a vision inspection system with our LCD products.  We would like to define pixel defects on a screen that is about 6.3" by 8.3" with a resolution of 1024x768.  We do not need anything that has high speeds since the test screens on the product will not change that fast.  Like everything else in business, we would like to keep this project cost to a minimum, especially since this is our first run at it.  Therefore, since we do not need high speed cameras like everything I see from machine vision manufacturers, can we use commercial digital SLR cameras.  They are relatively cheap, ~$1000, have high resolutions, >12MP, and can change lens' so that I can use these cameras with products that have different screen sizes and product depth.  We would need to inspect 6 cameras(6 UUTs) at a time and be able to have total control over all of them (focus, zoom, ISO, etc).  To do this, I found the following software:

http://www.breezesys.com/MultiCamera/index.htm

I believe that this can be called from labview because this software has DLL and exe files included.  The following is quoted out of their support manual:  "DSLR Remote Pro includes an interface library called DSLRRemoteLib.dll which can be used by other applications to control DSLR Remote Pro. Also included is a simple command line application called DSLRRemoteTest.exe which can be used to control DSLR Remote Pro from a command prompt or a batch file. For example a batch file could be written to take a series of photos using different apertures and shutter speeds to bracket the exposure.” 

Is this ok to use?  It has total control over multiple Canon DSLR cameras.  Am I going down the wrong path to inspect our products?  I didnt find any "regular" machine vision cameras with high resolution that are as "economically feasible."  Most are in the $4k-6k range which is much more than allowed.  Any help/comment from anyone is greatly appreciated!

Cheers,

Nick

[BruceAmmons]

Technically, you could probably do it with DSLRs, but I would not recommend it.  DSLRs are not designed for industrial use and are lacking a lot of features that can be found in machine vision cameras.

You would get better image quality using a grayscale camera.  You have to divide the resolution of the standard color DSLR in half (both axis) to get the equivalent grayscale resolution, roughly.

Moving images around will be more difficult with a DSLR.  It depends on the features of the driver.

In the long run, machine vision cameras may work out better.  Which ever way you decide to go, I would buy one camera and try it out before buying all six cameras.

Bruce

[NA_Skins]

What features would I be missing out on? As long as I get a good picture, isnt that all that matters. The only concern I have with DSLRs is that there might be some problems with post picture processing.  Do these cameras process the picture to make it look better, making the pictures inconsistant?

[Robert_Eastlund]

What you will probably find is that the 12 MP color camera is insufficient for single pixel defect inspection on a 1024 x 768 display.  You would be much better off with a monochrome camera for single pixel defect checks.    Unless the display is significantly oversampled by a color camera, the result of imaging a display with a color camera is an image processing nightmare.

I suggest inspecting the Red, Green and Blue pixels of the display separately by activating the R, G and B pixels of the display in sequence and using a monochrome camera with at least 4 camera pixels per display pixel.  You will also want to be at a relatively high focal length lens, so the further the camera can be away from the display the better.  This is because the light exits from the display's pixels at an angle and the camera lens has an acceptance angle.  If the acceptance angle of the camera lens is wide and the exit angle from the display's pixels is narrow, then the result is that in the middle of the camera image the display's pixels will appear to be dramatically brighter than the pixels at the edge of the display.

Given that the project has budgetary constraints, I would agree with Bruce's suggestion of purchasing the DSLR camera and taking the project as far as you can with it.  Assuming that you overcome the interfacing issues, you will be able to do a great deal of learning with the DSLR.  You will want to disable or have manual control of all of the camera's features, including exposure time, gain, gamma...  What you will be able to control depends on the DSLR that you purchase.  This is one of the differences that separates the consumer, professional and industrial cameras.  The industrial cameras allow you complete control of the camera's features.  There are also differences in the quality of the sensors used in the various cameras.

Good luck with the project!

-Robert