DSC-F55, DSC-F55E (serv.man2) - Sony Digital Camera Service Manual (repair manual). Page 24

The picture data from MS is written into the SDRAM in the form of Y, CR,
CB digital data having 2,000,000 pixels after expanded by the CAMERA
DSP (IC251).  This size of picture data is too large to be displayed on LCD.
Therefore, the picture data is processed of its signal by the CAMERA DSP
so that it is reduced to the VGA size, then it is again written into the SDRAM.
The Y, CR, CB digital data is sent to the CAMERA DSP again, D/A con-
verted and displayed on LCD.

When a specific area is sampled from the digital data that is stored in the
SDRAM, by operating the +/– button and the control button, the digital
data of the selected area is processed of its signal by the CAMERA DSP so
that size of the selected area is adjusted for the VGA size, and is written
again into the SDRAM.  The Y, CR, CB digital data of the selected area is
D/A converted by the SDRAM and is sent to the LCD for display.
Trimming is the function of writing the above described data into MS after
is it is compressed by the CAMERA DSP and writing into the SDRAM
(IC455.)