What is Optecal?

Optecal is a digital image correlation (DIC) software. But unlike any other DIC software, you can use a conventional digital camera (DSLR from Canon,Nikon, Sony etc…). You can load your RAW files directly into the software, correct lens distortions using the lens database and perform analysis.

Is Optecal free and open source?

Yes. Git repo available here.

What is digital image correlation?

DIC technique consists of tracking very small regions of a picture called subsets. In order to work properly, these subsets need to have very high contrast, that is why we usually paint black speckles on a white background or vice-versa. Since each pixel can capture very subtle shades of gray, it is possible to track the subset displacements and deformations with sub-pixel accuracy (~1/100th pixel).

What size speckle do you recommend for my specimen?

Your speckles should be between 4 and 10 pixels wide. If your speckles appear very blurry, you may have a poor quality lens, or a poor focus. If the problem cannot be fixed, you may consider using larger speckles, and run your analysis with larger subset size.

What lens should I use for my experiment?

You should use the longest lens possible, ie. the one that magnifies the most. It will minimize the error caused by the out of plane motion of your specimen. Prime lenses are usually cheaper and sharper than zooms, and their distortion is easier to fix. So you should favor them over zoom lenses. When using a zoom, try to use the tele end. If your specimen is very small, you may need a macro lens.

Is my camera compatible?

Optecal uses the LibRAW library to unpack RAW images. It is compatible with most cameras. You can also use the Adobe RAW image standard called DNG.

Is my lens included in the lens distortion database?

Optecal uses the Lensfun database to correct lens distortions. You can check their website to see if your camera is in their list. Or better yet, you can simply download Optecal and check if your lens is in the database.

Why Optecal can perform DIC using a DSLR, I thought only expensive monochrome cameras could do it?

Once an image is captured with a DSLR, it is transformed by numerous algorithms such as gamma curve correction, image sharpening, etc.. When shooting RAW, these transformations are performed during post-processing. Optecal uses a unique algorithm to process the RAW file images. In particular, the debayering algorithm used by Optecal allows to recover very fine motions, even with a color sensor. Since high-end DSLR have a much better resolution and bit depth than most scientific cameras, you will usually obtain results far better than results obtained with a scientific camera.

Can I use Optecal with any image file?

Yes. It is recommended to convert RAW files with Optecal, but it is possible to load most image file formats. Compressed images such as JPEG will give very noisy results, TIFF or BMP files from scientific cameras will work very well.