iMechanica - digital image correlation - Comments

Analyzing images without speckle patterns.

Prabhakar Rao — Tue, 18 Jan 2011 18:17:54 -0500

Dear Chris, Dan and Rob:

I am trying to use your code to analyze a series of high-speed images obtained as part of a low-velcotiy impact test procedure. Due to the limitations of the available equipment, I am able to capture one image at 50 µs intervals. As such, I have a set of 10 useful images. These images were acquired without any speckle pattern on them. The deformations are rather large and change significantly from one frame to the next. Also, I have observed that the results vary appreciably depending on the algorithm I use for deleting badly tracked markers. Could you please suggest the 'best' algorithm for this purpose based on your experience? Given the above background, could I still use your code to correlate the images and compute strains?

Many thanks for your feedback.

Best,

Prabhakar

DIC software

Mohammad R.Yadegari — Wed, 29 Sep 2010 12:22:55 -0400

Dear Dr Eberl

I tryed to go to that site for downloading DIC code for my master of science thesis.But unfortunatly I couldnt find that.could you please help me or send it for me to my mail.

sincerely

M R Yadegari

m.yadegari@ut.ac.ir

Thanks for the software

Siva P V Nadimpalli — Fri, 23 Oct 2009 14:21:06 -0400

Dear Chris, Rob and Dan,

Thank you all for providing this software free of cost. It is a big help.

I have one question regarding rigidbody rotations. If the specimen rotates or translates significantly during testing (due to loading arrangements), how can this be taken into account while using this correlation software.

Thanks once again.

Siva

Qhullmx error

karthiab — Mon, 18 May 2009 16:47:02 -0400

Qhullmx error

Hi Hassan, do you have

chris — Thu, 11 Sep 2008 18:39:10 -0400

Hi Hassan,

do you have the image processing toolbox installed? Sounds like it is missing as all described errors are are connected to funtion which are part of it.

Cheers, Chris.

Dr. Christoph Eberl
Nachwuchsgruppenleiter (DFG gefördert)
Universität Karlsruhe (TH)
Institut für Zuverlässigkeit von Bauteilen und Systemen
Kaiserstr. 12
D-76131 Karlsruhe, Germany
Forschungszentrum Karlsruhe GmbH
Institut fuer Materialforsc

Hi Shafqat, I think it

chris — Thu, 11 Sep 2008 18:36:32 -0400

Hi Shafqat,

I think it could be that peak_labelling does not find any good peaks any more. What does the image look like during analysis? Where there still peaks marked?

Chris.

Automate_image error

chris — Thu, 11 Sep 2008 18:33:57 -0400

Hi Todd,

that's some historical code which is not supported by matlab any more. I took it out in the newest upload on the matlab server. Cheers, Chris.

problem with matlab file!

H.Ghadbeigi — Sat, 16 Aug 2008 07:28:47 -0400

Hi chris,

first of all, thank you for your generocity,

then i have got some problem when running your matlab code, would you please tell me what to do to solve them?

1- i couldnt find "cpcorr.m" file in the attached zip foldes

2 when i run grid_genrator i will get the following messages:

??? Undefined function or method 'imshow' for input arguments of type
'uint8'.

Error in ==> grid_generator>gridtypeselection at 46
imshow(im_grid,'truesize');

Error in ==> grid_generator at 35
[grid_x,grid_y,FileNameBase,PathNameBase] = gridtypeselection(FileNameBase,
PathNameBase, im_grid);

i have to mention that i am using MATLAB R2008 on my X64 windows workstation.

Regards

Hassan, Sheffield

peak_labelling.m

Shafqat — Fri, 09 May 2008 06:21:08 -0400

I am having a problem when running peak_labelling. The error message is

??? Undefined function or variable "cropxy".

Error in ==> peak_labelling at 127
fitcountertemp=size(cropxy); % number off peaks to cycle through

can any body help me....

automate_image error

todd.gross — Tue, 26 Feb 2008 10:38:27 -0500

Hi,

The timedim function in the statement

[h,m,s] = hms2mat(timedim(estimatedtime,'seconds','hms'));

gives the error:

??? Undefined command/function 'timedim'.

Error in ==> automate_image at 135
[h,m,s] = hms2mat(timedim(estimatedtime,'seconds','hms'));

Has anyone run into this? I am using large images that I have converted from jpeg to tif using irfanview

Thanks in advance!

Color image correlation

powerlanger — Tue, 11 Dec 2007 18:43:01 -0500

I've modified the above

John W. Parker — Thu, 27 Sep 2007 17:32:18 -0400

I've modified the above code in findpeak.m to:

    % return only one-hundredth of a pixel precision
    x_offset = round(1000*x_offset)/1000;
    y_offset = round(1000*y_offset)/1000;

And then undid the second change to cpcorr that Christoph described in the correlation_guide_2 document to lines 134 and 135 (the ones that start "input_fractional_offset=. . ." and "base_fractional_offset=. . ."

I did some correlations on computer generated sub-pixel movements and proved these modifications to vastly increase sub-pixel accuracy.

findpeak.m

John W. Parker — Mon, 17 Sep 2007 17:18:45 -0400

It's a part of the imaging toolbox I think. It fits a second order polynomial to the data and reports the peak. What seems strange to me is this portion of it:

    % return only one-tenth of a pixel precision
    x_offset = round(10*x_offset)/10;
    y_offset = round(10*y_offset)/10;

So it appears that this is limiting the precision of the correlation to 1/10th pixel, and since this function is what is called on by cpcorr.m the change suggested in the users guide to this software won't do anything more then carry the decimal points form the original grid positions through the corrletion.

Changing it to 1/100 produced some strange looking results with similar precision as before. I'm still working on figuring out why.

findpeak.m

vikasargod — Tue, 21 Aug 2007 18:45:03 -0400

I found that the package needs a private program called findpeak.m.. can you please tell me the way in which i can get this file?. without that, its not possible to get this working for me

thank you!

regards

Vikas

displacement calculation

vikasargod — Mon, 13 Aug 2007 16:22:13 -0400

i am using your code to get strain calculation.. i am running into problems with qhull precision. basically when i use displacement.m, it gives an error when it calls griddata. I am running for the same copies of images for understanding purpose. I am in Linux with matlab 7.4 in 64 bit. (error is meshplot in line 670).

i observed that if i use only two images (by commenting the code for loopimages), it gives an error that 'matirix exceeds dimensions' at validx(:,3:10) ...etc

can you please help me?

regards

Vikas