I'm taking tshirt pictures with my phone, but even with 2 softboxes, the plain white shirt is a darker gray in some area. Do I only do it in a dark room with no light coming in or is it because the phone's camera makes it darker, or should I use a DSLR instead? thank you so much (:
This sounds like the same problem people encounter when trying to photograph snow on automatic exposure. The camera will adjust the overall light value in your image to approximate middle grey. When the image is dominantly white, as in your case, the camera darkens the image, and I expect your smartphone is doing the same thing.
In a DSLR, you can compensate for this by opening up your aperture beyond what your light meter advises (keeping an eye on the histogram to avoid blowing out the highs). Try changing the exposure on your cell phone to see if that helps. If not, then you have the DSLR option.
There are two things probably going on here...
The first is a metering issue...Cameras are smart, but they're not people. The meters assume a scene that is middle of the road, not super contrasty.
So, if you hold a perfectly white board up in front of your camera and take a photo, then you'll get a photo of a grey card.
Likewise, if you hold a perfectly black board up in front of your camera and take a photo, then you'll get a photo of a ... you guess it ... grey card.
This is the reason why images taken in bright environments (think snow) are often underexposed while images taken in very dark environments often blow the exposure for those elements receiving more light.
In order to solve for this, you need to override your camera. If shooting a white object, then expose more! Tweak the exposure settings to use either a higher ISO or a longer shutter speed, or both. (Do a longer shutter first, if you max it, then pursue ISO changes).
The best image is the one where there are whites just on the verge of blowing out. Some blown highlight marks are okay.
More info on this topic can be found here: https://www.slrlounge.com/when-your-camera-meter-is-wrong-and-what-to-do-about-it/
The second is a reality check...Take a look at the shirt below:
Notice that the left side armpit is completely blown out along with the left side collar. The line where the collar ends is still visible and you can still tell it is a collar...but the fact that all detail is gone from it deters from the photo. Lessening the exposure so that only the top-most hard edge blew out as a highlight and texture on the collar remained would have been better.
Note that the left side being blown out has stripped all detail from a large chunk of the left side of the shirt. This is blown out - not a highlight. The exposure should have been lowered or lights moved further out for this shot.
But, notice that where there is detail on this white shirt, you perceive it due to the interplay of highlights and shadows.
Your white shirt photograph will never be perfect white all across the board. Indeed, the best image of a white shirt for product sale will be one that has highlights just on the edge with nothing blown out on the actual shirt. If you want to trick the viewer's eye into thinking things are whiter than they are, then photograph a white shirt on a black background to make it pop more.