• Fix LRF
It was noticed by many Sony Reader users that quality of images and text on the PRS-500 and PRS-505 screens depend on the file type. I personally was always surprised by grayish look of PDF documents and their significant improvement after transferring to LRF files ("LRF pictures") even if no filtering was applied.
Here I prove the following:
1. PRS-505 uses 8-level gray scale for images and font rendering in LRF files (in contrast to 4-level palette in PRS-500).
All the following is about frame buffer content. How this content will look on a real e-ink screen is another subject. Sony does special care on palette mapping only in LRF files.
LRF font rendering
Fig 1a and Fig. 1b show magnified area of 2 characters. We can see that pallets used for font rendering are different. The 4-gray pallet and 8-gray palette were tested over integration of the full screen area. The pallets correspond to the pallets discussed below in 256-gray color experiment.
RTF and TXT font rendering
TXt and RTF font antialiasing uses 256-level palette in both PRS-500 and PRS-505, this was checked over the full screen area. Have a look how "o" differs from the "o" in LRF files.
Fig. 4 and Fig. 5 show PDF file, gray background is clearly seen on PC screen. You can also see this background on PRS screen, though less noticeable. This background is always part of any PDF file (independent on the program used for PDF creation).
The pictures in LRF files are treated differently for PRS500 and PRS-505, you may see different dithering algorithm in the above example. Images in PRS-500 are converted to 4-level palette, images in PRS-505 are converted to 8-level palette. The pallete mapping is discussed below. While "wrapping" PDF to LRF file pictures, the PDF's 256-level palette is being converted to 4, or 8 level pallets correspondingly.
To check pallets mapping some test LRF file was created. This files includes 256 objects of the "line" type, each of 1 pixel thickness. Every 5 and 10 line is a little bit longer to produce "ticks" for the counting. The colors in LRF files are in the 0x00RRGGBB format, the color of the each individual line was 0x00iii, where i=0; i<256.
Here is how this file looks like in the "Ebook Library" (or "Connect") programs (screen capture), in PRS-500 and PRS-505 (screen bitmap).
The mapping is not uniform, the "gravity center" is shifted toward darker colors.