OpenCV load CIE L*a*b* image - c++

Question

I'm trying to load a CIE Lab* image using openCV in C++.
Online I can find only examples that load an RGB image and convert it into a LAB image but I already have the LAB image so how can I load it and than access to the values of L, a and b?
The only way I find is to load the LAB image considering it an RGB image and convert it into a Lab image using:
cvtColor(source, destination, CV_BGR2Lab);
But I think this is not a good way to solve the problem because if I do this, the converted image looks very different from the original.
With a test image and the following code:
originalImage = imread(originalImagePath, CV_LOAD_IMAGE_UNCHANGED);
cout << originalImage.type() << endl;
Mat originalImageSplitted[3];
split(originalImage, originalImageSplitted);
cout << originalImageSplitted[0] << endl;
cout << originalImageSplitted[1] << endl;
cout << originalImageSplitted[2] << endl;
I get the result:
0
[]
[]
[]

Answer 1

Not really an answer, but too much for a comment.
You can make a Lab colourspace TIF file for testing like this with ImageMagick from the Terminal in Linux, macOS or Windows:
convert -depth 8 xc:black xc:white xc:red xc:lime xc:blue +append -colorspace Lab result.tif
That will look like this if I scale it up as it is currently only 5 pixels wide and 1 pixel tall:
You can then dump the pixels to see their values and hopefully work out what OpenCV is doing:
convert result.tif txt:
Sample Output
# ImageMagick pixel enumeration: 5,1,65535,cielab
0,0: (0,-0.5,-0.5) #000000 cielab(0%,-0.000762951%,-0.000762951%) <--- black pixel
1,0: (65535,-0.5,-0.5) #FF0000 cielab(100%,-0.000762951%,-0.000762951%) <--- white pixel
2,0: (34952,20559.5,17218.5) #885043 cielab(53.3333%,31.3718%,26.2737%) <--- red pixel
3,0: (57568,-22102.5,21330.5) #E00053 cielab(87.8431%,-33.7263%,32.5483%) <--- green pixel
4,0: (21074,20302.5,-27756.5) #524F00 cielab(32.1569%,30.9796%,-42.3537%) <--- blue pixel
Looking at the red pixel, you get:
L=53.33%
a=31.37% of 256, i.e. 80.3
b=26.27% of 256, i.e. 67.2

Answer 2

To keep the image unchanged you should read it into a Mat image similarly:
Mat image;
image = imread(<path_of_image>, CV_LOAD_IMAGE_UNCHANGED)
In this case the second argument should preserve your image color channels as is.

Answer 3

With #DanMašek using #MarkSetchell image we solved the problem.
Using imread function the image is automatically converted into an RGB image so it's needed to convert it into a Lab image again.
Another problem is releated to 8bit images. The resulted image has modified values of L,a and b following this rule:
L * 255/100
a as a+128
b as b+128
So I solved doing the following:
originalImage = imread(originalImagePath, CV_LOAD_IMAGE_UNCHANGED);
Mat originalImageLab;
cvtColor(originalImage, originalImageLab, COLOR_RGB2Lab);
Mat originalImageSplitted[3];
split(originalImageLab, originalImageSplitted);
Thank you all!