Gray value analysis - Histogramm - Curve inside of the curve

hope one of you guys can help me out. For my master thesis I have to evaluate the homogenisation of blown film.
I scan the film, change it to a gray value image (with gimp, paint shop pro or ImageJ) load it into ImageJ, select my area and open the histogram.
For some reason there is always a 2nd curve inside the curve. Every 2nd value changes drastically in respect to the value before. Below I uploaded the same scan with how the histogram should looke like on the left and how it always looks like on the right. I don’t know what difference exists between those 2 images.
Hope someone gets me and knows how to solve that. Thank you! :slight_smile:

Hi @PhilE,

JPGs are known to contain artifacts, so if you can save your scan in RAW or TIFF format it would be better for quantitative analysis.

To figure out the answer to your question, a little more detail would be helpful:

  • What is the original format of the scan?
  • How do you “change it to a gray value image”? (what command in ImageJ do you use?)
  • If the image on the left is how it should look, how did you get that one?

It would also help if you could upload a small sample image before and after conversion.



thank you for your reply. I change it with a makro to an 8-bit image in ImageJ.
I kind of found the solution. The file size differed a lot so I checked my scanner.
Don’t really know what I changed but it works now! :slight_smile: