I have seen your tech support case escalation, and I have looked at the file you sent to MathWorks.
The MATLAB function imread never compresses image data when reading image files.
Here's everything I was able to find out about your CR2 file.
The file is (mostly) in TIFF format. It contains 4 IFDs (Image File Directories).
The image described by IFD #1 is 4480x6720, 3 samples per pixel, stored in the file using OJPEG compression (indicated by TIFF compression type 6). OJEG stands for "old-style JPEG compression" and has been considered obsolete since TIFF Technical Note 2, 1995. The first image can be read using:
A = imread('IMG_0042.CR2',1);
When displaying it using imshow, a star field is visible. This is the image you get when you call imread using only one input argument, like this:
A = imread('IMG_0042.CR2');
The pixel data for image #1 uses 1,313,151 bytes in the file, for an average of 0.044 bits per pixel, suggesting the data is heavily compressed.
IFD #2 is not a valid Image File Directory. It contains only two tags: a JPEG Interchange Format tag, and a JPEG Interchange Format Length tag. Both are obsolete.
The image described by IFD #3 is small, only 284x430. It is uncompressed (TIFF compression type = 1). The image from IFD #3 can be read using:
C = imread('IMG_0042.CR2',3);
Displaying it requires scaling, however, because the pixel data type is uint16 and the maximum pixel value is much less than 65535.
The image described by IFD #4 is puzzling. It is 4544x6880, with old-style JPEG compression (TIFF compression type = 6). It has four proprietary vendor tags used for Canon CR2 files. The pixel data uses 29,740,944 bytes in the file. However, reading it in using:
D = imread('IMG_0042.CR2',4);
produces an all-green image, with the red channel pixels = 0, the green channel pixels = 135, and the blue channel pixels = 0.
I speculate that compression type 6 (OJPEG) stored in the file is actually a lie. Based on the number of bytes used in the file to store this image, I guess that it is losslessly compressed using some proprietary scheme.