Converting RGB to CIE Lab

Hello,

I am wanting to obtain Lab colorspace values for some images that I have. I am using jpeg images and converting them from RGB to Lab using Image > Color > RGB to CIELAB in Fiji.

However, if I check the RGB values of one pixel in the RGB image and compare it to the Lab values of the same pixel in the CIELAB image and run it through a mathematical converter in Excel, the pixel values are off.

For example, in my RGB image I have a pixel at 112, 045, 078 for RGB values. According to a mathematical converter, the Lab values should be 29.09, 33.54, -5.58. However, the values I get from ImageJ are 39.3662, 41.3999, -7.3332 for the Lab pixel.

Is there a calibration that is needed for the conversion? Or is using a jpeg image causing an issue? I’m unsure as to how ImageJ is calculating the conversion values.

Any suggestions would be greatly appreciated.

Thanks!

I just tried Image>Type>Lab Stack instead of the RGB to CIELab conversion process and this seems to match the mathematical converter.