Question about time to write Data to IT8951 Framebuffer.

[tobiasaska]

Hello,
I am working with Raspberry Pi 3 and the 10.3" Epaper Display from Waveshare. The refresh rate is very fast but the time to write the data from host frame buffer to IT8951 Frame Buffer is about 10 seconds. This is way to long for my application. Is there any way to make this process faster? Or can write multible images to different Frame Buffers on the IT8951? Has this to do with SPI interface?

[JorgosCoenen]

From my experiences, the size and detail of the image seems to make a difference. Converting the image to a C-file before or using the IT8951 bmp-conversion function doesn't seem to make too much of a difference.
Experimenting with partial updates where you only have to push a select buffer size can also help.

For now, designing for e-ink screens still seems to require thinking around the limited refresh rate.

But curious if waveshare has any suggestions too!

[tobiasaska]

From my experiences, the size and detail of the image seems to make a difference. Converting the image to a C-file before or using the IT8951 bmp-conversion function doesn't seem to make too much of a difference.
Experimenting with partial updates where you only have to push a select buffer size can also help.

For now, designing for e-ink screens still seems to require thinking around the limited refresh rate.

But curious if waveshare has any suggestions too!

Thank you for your reply.
The problem does not seem to be the actual refresh rate which is around 450ms. The problem is the time to write the image from host frame buffer to IT8951 frame buffer. This takes 10 seconds using your demo code running on raspberry pi 3. For example when I use the demo program for windows providet by waveshare it doesnt take that long. How can I display a new image every 450ms or at least every second ?

[JorgosCoenen]

I'm not part of waveshare, so I'm not sure... We've also noticed that the Windows application seems faster.
Are you pushing full resolution bmp's? Don't small images or graphics from the other demo functions go faster?

[naluhh]

I made it ~10 times faster by not using LCDWriteData but writing my own function that internally send all the data in one call. I also switched to 4BPP instead of 8 and made it again 2x faster. @tobiasaska

[JorgosCoenen]

That sounds amazing @naluhh!
Any plans to share your changes? Would love to try them out!

[naluhh]

I made a quick test yesterday. I'm trying to make it even faster by extracting the picture directly into a 4bpp texture. I'm only planning on doing full screen updates. I'll share some code this week

[tobiasaska]

I made it ~10 times faster by not using LCDWriteData but writing my own function that internally send all the data in one call. I also switched to 4BPP instead of 8 and made it again 2x faster. @tobiasaska

@naluhh Thank you very much for this piece of information. Thats exacly what i was looking for. I am pretty new to coding. Would you mind sharing your code with me/us?

[naluhh]

#3

It's a work in progress. But you can try like this:

make
sudo ./IT8951 path_to_image.bmp

[tobiasaska]

#3

It's a work in progress. But you can try like this:

make
sudo ./IT8951 path_to_image.bmp

Thank you! I will try this 👍

[JorgosCoenen]

Tried it just now. Very noticeable speed boost! Awesome! Thank you!
I think you also managed to move to 4bpp? Anyway to also include 8bpp as an option? Or would that reduce the performance boost significantly? You mentioned that even with 8bpp your changes were much faster.
My application has some images that require the higher resolution...

[naluhh]

@JorgosCoenen 4BPP is the maximum these screens can do anyway. Right now it's decoding the BMP in 8bpp and I then translate it to 4bpp. It would be much faster (less allocation, smaller file etc) to have a 4bpp image (png support it). I'm sure other optimizations could be done.

[JorgosCoenen]

Aha! What could than be causing the loss of image quality, if it's always 4bpp anyway?
It kind if looks like anti-aliasing or interlacing. Just trying to understand :)

Here are some images: original, and update.

[naluhh]

Could you try to replace this line:

stLdImgInfo.usEndianType     = IT8951_LDIMG_B_ENDIAN;

by

stLdImgInfo.usEndianType     = IT8951_LDIMG_L_ENDIAN;

[JorgosCoenen]

Sure! Seems this makes the "interlacing" more pronounced.
An image.

[naluhh]

What's the resolution of your screen?