[IMPROVEMENT] Modify -quant 0 option

[thealphadollar]

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This pull request aims at simplifying and making the -quant 0 parameter faster. It does so by reducing the number of distinct color shades available in the palette of the PNG image under processing.

An example would be, say a palette color is (248, 187, 027). The new algorithm reduces this image to (224, 160, 0). This is one quantised value amongst the (888) which can be formed under this algorithm. Since the color palette is reduced and our rect bitmap structures point to palette for their pixel color value; in a way this algorithm decreases the color value to the nearest multiple of 32 for R,G,B; effectively quantising it without much reduction in the actual image visibility.

As can be seen in the below screenshot, this method improves the time taken (92 seconds vs 100 seconds) and also gives a better result than no quantisation.

As is marked in the below screenshot (with no quant algorithm at all), a dialogue is read as "Are you off the deck". This is a mistake which does not happen and is read as "Are you off the clock" with the improved algorithm. The video is provided along with the timestamp to check for authenticity.

At last below is a diff between the two files to see the other error corrections that the method provides, (for example it correctly reads "I" (capital "i") which were read as "|")

For video file, refer issue #929

Minor Addition: Added below line which can be uncommented to output debug.png from ocr_bitmap() function
save_spupng("debug.png", indata, w, h, palette, alpha, 16);

[cfsmp3]

• case 0 means "pass the image unchanged to tessearact", so it cannot do any kind of processing.
• You can add that new code to case 2 (but test that it actually helps in some cases, otherwise no point in adding it)
• Remember that the help text needs to be updated as well.

[thealphadollar]

The proposed algorithm improves speed and gives slightly better results as is shown in the PR content.

Updated help and made it case 2 :)