Thread View: alt.graphics.pixutils
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Started by Willem van Schaik
Fri, 22 Jan 1993 23:56
PPM to CD-I formats (clut-8,dyuv,rgb 5:5:5,rl 3/7)
Author: Willem van Schaik
Date: Fri, 22 Jan 1993 23:56
Date: Fri, 22 Jan 1993 23:56
24 lines
1255 bytes
1255 bytes
Hi pix-land, 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. Also PBMPLUS couldn't help me out. Therefore my request to net-land is if anybody has a utility that can generate one or more of these formats. The specifications of these formats would also be handy, because then I will write the converter myself. And ofcourse you can find it then in a while posted overhere. Please, please, help me ... Willem van Schaik schaik@cnplss5.cnps.philips.nl
Re: PPM to CD-I formats (clut-8,dyuv,rgb 5:5:5,rl 3/7)
Author: Chris Lilley
Date: Tue, 26 Jan 1993 16:31
Date: Tue, 26 Jan 1993 16:31
57 lines
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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 --------------------------------------------------------------------------- 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 Voice: +44 (0)61 275 6095 Fax: +44 (0)61 275 6040 ---------------------------------------------------------------------------
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