Support for Inky Impression - 7.3” (2025 Edition) PIM773

[Cironic]

on the new Version the missing color makes pictures looking odd.
Is there any way to adjust the way the pictures are displayed?

[helgibbons]

It might be worth trying reducing the saturation level if you've not done that already?

inky_display.set_image(image, saturation=0.5)

When I was playing with comics, values between 0.0 and 0.2 seemed to work better with lighter images. The default value (0.5) sometimes over-dithered the highlights into white oblivion.

This issue contains some interesting information (and comparison photos) showing how the saturation value effects how colours are displayed on the new Spectra 6 display.

[phattmatt]

It was confusing to me that reducing the saturation value increased the number of colours that ended up being rendered on the screen.

I've run some tests on my "Inky Impression - 7.3” (2025 Edition)" and I'm a little confused how the saturation is working.

I used the 'image.py' example with the inky library (version 2.2.1) to show a colour chart on the screen. I added an 'image.save' to the 'inky/inky_e673.py' file to take copies of the images just before they are sent to the screen.

These are some of the results (I've attached a zip file with images from 0.0 to 1.0 saturation values):

Original Colour Chart

Saturation 0.0 (renders the most colours)

Saturation 0.5 (default value , some colours are blown out to grey/white)

Saturation 0.9

The images above are representative of what I'm seeing on the Inky Impression.

As can be seen, decreasing the saturation value seems to actually increase the saturation.

Increasing the saturation value results in a washed out appearance, and less colours being rendered.

Am I misunderstanding something? Or, is this expected?

All the test images (from 0.0 to 1.0 saturation values)
spectra73_test.zip

[Gadgetoid]

Saturation is, perhaps, a little misleading since it's normally understood as you're expecting. However it's not attempting to control the saturation of the final image (somewhat difficult since the colours of the display are immutable) but rather the saturation of the palette to which an image is dithered to.

So a saturation of 1.0 would use a red value of 255,0,0 whereas a saturation of 0.0 would use our "take a photo of the screen in neutral lighting and use a colour dropper tool" value of 156, 72, 75. You can see these two palettes here:

https://github.com/pimoroni/inky/blob/fcf264372fa41b07e37ca4b41198d5cd4a5ad026/inky/inky_el133uf1.py#L20-L36C21

As such the "saturation" value is more a compensation for the saturation of the source image, helping to coax the dithering algorithm toward selecting the closest "green" rather than simply the mathematically closest colour under some circumstances.

This is discussed and explored a bit more here: #115 (comment)

The TLDR is that true-to-colour dithering on the e-ink display often results in pretty underwhelming colours, especially where there are bright, saturated colours involved in the source image, and this is an effort to give some control over compensating for that.

[phattmatt]

Hi @Gadgetoid,

Thanks for the reply, I appreciate the explanation and links.