🚀 go-pugleaf

In article <1993Jan22.235652.2826@cnplss5.cnps.philips.nl> schaik@cnplss5.cft.philips.nl (Willem van Schaik) writes:

>I need to convert some .ppm format pictures to any format
>which can be used for CD-I. The formats supported are
>
>	clut-7
>	clut-8
>	dyuv
>	rgb 5:5:5 
>	rl 3/7
>
>To be honest, I thought I knew already about a lot of graphics formats
>however, these are all new to me. 


Well lets see - clut is probably colour lookup table, in other words
indexed or pallette colour. I would guess that 7 and 8 are the number
of bits used to index the table, giving 128 or 256 entries. That would
mean each pixel fits in a byte. So to convert a PPM to one of these,
you need to quantize down to 128 or 256 colours. Various utilities -
URT, the JPEG stuff, and PBM+ for example - will let you do this.

You will need to find out how many bits you get for each clut entry.

dyuv - erm - possibly something to do with TV yuv encoding. It is just
possible that the d means differential, in other words each pixel
stores the change from the previous pixel. Then again I could be and
probably am way off on this one...

rgb 5:5:5 is clear enough - a true colour image with 5 bits each for
r,g and b - like 24 bit images have 8 bits each. So you need to round
off the 8 bit values to 5 bits or (quicker and less accurate) truncate
them to 5 bits by shifting.

Depending on how many colours are in the image and how many bits are
used in the clut modes, this could be better or worse than clut-8. For
example an image with lots (well, more than 256) of different colours
will likely be better in this rgb555 mode which can contain (32 =
2**5)*32*32 colours - 32768.

An image with fewer than 256 colours could look better in clut mode if
the clut entries are more than 15 bits wide.

rl 3/7 no idea - run length encoding of some sort?

Hope this is some help, anyway.



--
Chris Lilley
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Technical Author, ITTI Computer Graphics and Visualisation Training Project
Computer Graphics Unit, Manchester Computing Centre, Manchester, UK
Internet:   lilley@cgu.mcc.ac.uk        Janet:   lilley@uk.ac.mcc.cgu
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