Most digital cameras have an
anti-aliasing filter in front of the image sensor to control
moiré.
That filter diminishes image
sharpness.
Consequently, most digital photographs need to be sharpened post process.
The best results are obtained by sharpening in a 3 stage process:
Light global sharpening of a Raw file - global meaning the entire image file is sharpened equally.
Local sharpening - local meaning only sharpening areas of a photo, like just the t-shirt in the photo and not the background.
And lastly output sharpening according to how the photo will be used. Photos for online display cannot be sharpened as much as photos that will be printed.
The worst place to do that sharpening is in the camera because the in the camera sharpening controls are very crude and are global.
If you are recording the t-shirt photos as JPEG files the camera is applying sharpening to the entire photograph.
The JPEG file type was designed to be a final ready-to-print file type that won't be edited any further.
Consequently JPEG files are limited to being 8-
bit depth files. 8-bit depth files have little editing headroom, and many 8-bit depth files have no editing headroom.
Most DSLR cameras today make Raw files that have a 12-bit or 14-bit depth.
The additional bit depth provides lots more editing headroom.
Once the editing is done, then the image file can be converted to the JPEG file type.
Photo Editing Tutorials
Note that the ins-and-outs of digital photograph sharpening is a book length subject:
Real World Image Sharpening with Adobe Photoshop, Camera Raw, and Lightroom (2nd Edition)