First of all, sorry for digging up a relatively stale thread...
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Given the terrible rendering of covers in sleep mode, I quickly enabled the "B&W Covers" setting, but when that didn't help much, I took a look at the code: it basically just does what's on the tin, without dithering it down to the eInk 16 shades of grey palette.
Since I was in a hurry, I took a very dirty approach and applied this simple patch to the Calibre sources:
Code:
diff --git a/src/calibre/utils/magick/draw.py b/src/calibre/utils/magick/draw.py
index 73832a1..d0793c4 100644
--- a/src/calibre/utils/magick/draw.py
+++ b/src/calibre/utils/magick/draw.py
@@ -75,6 +75,7 @@ def save_cover_data_to(data, path, bgcolor='#ffffff', resize_to=None,
if grayscale:
img.type = "GrayscaleType"
+ img.quantize(number_colors=16, dither=1)
changed = True
if resize_to is not None:
It's dirty as hell, but it appears to be doing the job just fine. (Granted, the quantization step is expensive and appears to block the GUI, but, it works, I can now look at book covers without making my eyes bleed ;p).
I'm basically just throwing the idea out there to see if there's a way to handle that more gracefully
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[Granted, my opinionated position on this issue most likely stems from the pains I took to do it right with the Kindle's ScreenSavers hack
]