Projects that can be performed by FPGA based signal processing, have no border and no end. With the advancement of technology, field of FPGA applications is rapidly expanding. There are many new fields to work with FPGA such as :

MIMO detection in digital receivers, ICA, matched filter, sonar applications, Blind channel equalization, image and audio processing, DVB, Advanced channel coding techniques, Pattern recognition, and ... .

In Image Processing which is current hot research field?

There are many research areas in image/video processing that need FPGA implementation for real-time applications:

1. Super resolution

2. Image enhancement methods

3. Compressive sensing

4. Object identification and tracking 

5. Optical and Infrared/Thermal image fusion

6. Motion vector analysis

7. Camera calibration 

I'd suggest to also look into GPU processing using CUDA. The implementation time is much shorter and testing is much easier than FPGA. 

In addition to the topics proposed by Mohammed Mobien, I suggest you to check out related articles about FPGA implementation of Image Encryption methods.

THANKS sir for your Suggestions 

Good Luck.

My supervisor says, FPGA based implementation of existing technique may be good project but not research topic since it lacks novelty.

Example RCM, DWT implemention in image processing on FPGA cannot be approved as someone thesis but dissertation report of UG or PG Project.