Hi,
In some case it may indeed reduce the CPU load but this is not what should be expected when changing the color format.
Changing from 24 bits to 16 bits means that each pixel of the frame buffer will use 2 bytes instead of 3 thus reducing the memory area needed to store the frame buffer.
It will also reduce the general memory bandwidth, notably on the FMC bus.
On the display side the LTDC will transfer less data to update the display (if the display supports 16 bits data).
The CPU is not involved at all in the process of refreshing the display so no difference.
If the display still requires 24 bits data then only the frame buffer will be in 16-bits.
On the rendering side (frame buffer update) the ChromArt hardware accelerator is used for most of the pixel operations (copy, copy with transparency and pixel format conversion) so you may observe a CPU drop only if you use transformations such as scaling or rotation for example.
Again if you replace you input images by 16 bits versions you will save FLASH memory, but not CPU usage since the ChromArt is able to access these data without the help of the CPU.
So in short you should mostly expect to reduce the memory usage and memory bandwidth when changing the color format from 24 to 16 bits.
Best regards,
Nicolas
