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Old 03 February 2020, 18:08   #1
Retro1234
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Two Identical 16 colour Images?

I don't have access to a decent computer or I would test myself

We have a 16 colour IFF we save it in HAM format but it is only 16 colours what Image/File will have the larger size? Or will they be the same file size?

Why I ask, HAM is Supposed to have some lossy compression.
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Old 03 February 2020, 19:33   #2
DanScott
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A 16 colour image is 4 bitplanes... a HAM image would use 6 bitplanes... so the HAM image would be bigger.

There is no compression with HAM, other than the way it uses the bitplane data to either read a colour from the palette, or to modify one of the previous pixels R,G or B values
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Old 03 February 2020, 19:49   #3
Retro1234
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Thank you for your reply sir
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Old 03 February 2020, 23:57   #4
DamienD
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What exactly does this thread have to do with Creation > Graphics > Graphics. Work In Progress?

...moved accordingly.
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Old 12 February 2020, 00:19   #5
Retro1234
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What compression type does IFF use for instance we have Two images 320*256 one is a very detailed image the other is just A box, both images are the same size and amount of pixels but the one of the box has a much smaller file size.
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Old 12 February 2020, 07:51   #6
Solo Kazuki
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IFF-ILBM could be optionally compressed (which is probably in Your case) with RLE compression.
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Old 12 February 2020, 09:09   #7
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Just to add to Solo Kazuki, RLE compression is lossless.

Normally uncompressed images save pixel info as: pixel # is value #, next pixel # is value #, etc. For NLE compression, If pixels of common colour are next to each other the info is saved as follows: pixel # to pixel # is colour value.

So images with lots of fine detail won’t see a huge saving, but images with lots of solid areas of colour will.
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Old 12 February 2020, 12:56   #8
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What I'm think is if we can have a transparent colour in CDXL

Like MPEG we can Compare each frame by frame and only update the parts needed
[ Show youtube player ]
On stuff not moving much we save alot and could get a lot more smaller file size.
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Old 17 March 2020, 15:46   #9
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I think you're thinking about delta compression that yafa already uses.
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Old 17 March 2020, 16:06   #10
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I think it's called I frame or something but simpler I don't know much it would save a test could be done with ImageMagic.
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Old 17 March 2020, 22:14   #11
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Quote:
Originally Posted by DanScott View Post
A 16 colour image is 4 bitplanes... a HAM image would use 6 bitplanes... so the HAM image would be bigger.

There is no compression with HAM, other than the way it uses the bitplane data to either read a colour from the palette, or to modify one of the previous pixels R,G or B values
This is effectively (mathematically) a lossy compression format, in that it compresses a 12-bit image down to 6 bits by throwing away 2 of the 3 RGB channels for a given pixel. It's crude and simple but it's definitely compression (akin to the subsampling compression used in MPEG where they throw away 3 out of every 4 chroma samples -- in fact this is more like how HAM was originally supposed to work back when it was intended to operate on a YUV space).
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Old 23 March 2020, 23:37   #12
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Does yafa compare images like static backgrounds?

presumably applying compression like xpk to them wont increase FPS etc because the player doesn't know the overall file is smaller

it would require a new player so instead of just streaming frame by frame it could look at the file size and decide ok instead of just streaming 1 frame it can stream such amount and such amount of data like 1 and half frames with my limit of 300kb transfer.

I still think comparing frames could work especially if you remove noise and make an allowance for say a 10% difference of each 16*and 16 square of the image - wouldnt require any extra CPU to decompress, it would already be decompressed etc.
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Old 24 March 2020, 12:09   #13
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Now you got me thinking. I thought that yafa compares frames but it probably compares just certain selected consecutive run of bits byte, word or long.
Maybe xpk cant help on 020 but on 030 I'm pretty sure it could.
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