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Old 21 October 2016, 11:39   #41
pandy71
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Well this has been very interesting, thank you everyone! I appreciate all the input. That's a good point about RAM usage, can anyone let us know what the ram usage for a 320x200 ham8 screen? I'm not entirely sure how to calculate it to be honest, is it an 8-bitplane screenmode?
8 bitplanes means 1 byte - number of pixels (320x200) directly can be used for number of bytes, for less bit-planes i.e. less bits per pixel you can use formula like: ((X*Y)*n)/8 (where n is number of bitplanes).
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Old 21 October 2016, 12:53   #42
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8 bitplanes means 1 byte - number of pixels (320x200) directly can be used for number of bytes, for less bit-planes i.e. less bits per pixel you can use formula like: ((X*Y)*n)/8 (where n is number of bitplanes).
Yeah, I understand that, I just wasn't sure if HAM8 used 8 bit planes, or more or less. I guess I should have had a better think about it. Seems to me that HAM8 gives close enough to a true colour capable screen, while using the same amount of memory as a 256 colour screen of the same resolution, with the restrictions mentioned earlier in this thread. Even with the restrictions and the need to choose the indexed colours carefully to match the picture, this still strikes me as a fantastic technical achievement.

Unless I'm doing this incorrectly, it seems to me a 320x200 HAM8 screen would only require 64,000 bytes of Chip RAM?

So a 1280x512 HAM8 screen would require 666,360 bytes of Chip RAM, while for the same resolution if it were using a full 24-bit for each pixel would require 3 times as much, a whopping 1,999,080 bytes, and if the indexed colours are chosen well, it would be hard to tell apart the two colours with the naked eye. Or am I far off here?
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Old 21 October 2016, 13:04   #43
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Or am I far off here?
No, you're not... In fact, you're spot on..
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Old 21 October 2016, 13:12   #44
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Or am I far off here?
Nope - all is correct - think about HAM as very crude, simplistic lossy compression (with few exceptions where it is lossless) - some form of adaptive delta where at once only one of three video signal components can be modified.
This is one of the first (but not first) HW compressed framebuffers.
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Old 21 October 2016, 13:39   #45
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And, once again, I could be wrong here, but the maximum displayable colours on that 1280x512 screen would be 666,360, as that is how many pixels there would be on that screen, with it being possible to have even more with overscan, correct?

In any case, even on a 1920x1080 screen you still couldn't show every possible 24-bit colour, as you'd only have 2,073,600 pixels, far short of the 16,777,216 colours available in the full 24-bit palette, although in practice a number of the darker shades would be close enough to black to make no real difference? I mean, 0x010100, 0x000101, 0x010001, 0x000001, 0x010000 and 0x000100 would all be practically the same as 0x000000, correct, as they'd all be so dark as to be practically black?

I find this tricky, as I'm somewhat colourblind - I have moderate deutans (“doo-tans”), which means I have a moderate form of red-green color blindness. So there are a number of shades of colours that I can't tell apart, that others can. So I accept that I could very well be wrong on perceptions of colours.
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Old 21 October 2016, 14:02   #46
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Perception is highly individual also related to training, equipment and ambient conditions, also content related - i assume single pixels will be extremely difficult to evaluate single bit difference however for large areas and all optimal conditions human eye may distinguish between 10 and 12 bits (depend on individuals and their practice) of luminance yet our colour perception is limited - some scientists saying on around 10 million unique perceived colours... i think this is underrated... and we are in close to 30 - 36 bits per component.
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Old 26 October 2016, 11:45   #47
Jack Burton
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Just out of curiosity I made a test on ImageFX 2.6 with an image representing the 24bit full color palette. Of course as it was expected my A1200 couldn't display a 4096x4096 image, I got some memory errors.
Well, at least I could load the picture since I've 128MB of RAM on my A1200. So I cropped the image to 1280x1280 wich was the absolute limit before getting some memory errors again.
Then I rendered it in HAM8 (HiRes HAM laced), saved the pic and loaded it to count the colors from the buffer. I repeated the test cropping the image to 1024x1024 and 512x512.

Here are the results :

1280 x 1280 -> 41082
1024 x 1024 -> 16775
512 x 512 -> 12296

In my case I was far from 262144 colors here...

Oh, the croped zone was simply the upper left corner. As the image is divided in 256x256 squares, the max I could crop was 5x5 squares (1280x1280 pixels).

If someone want to make the experiment, I put the original 16MP image in the zone.
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Old 28 October 2016, 10:05   #48
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Hello

@Jack Burton
just tried with your example picture using my own DatatypeToHam program
(in WinUAE with lots of ram)

DatatypeToHam 144 Full_24bit_RGB_palette.png 4096 4096

I have obtained an iff ham file but too big for any classic amiga (but for info it load on a Sam460 +OS4.1fe)

Then I load it in XnView for PC (that have nice ham8 loading support) ==> 258304 colors
PaintShopPro give same result once converted to BMP

So the message is : DatatypeToHam CAN generate a REAL 258304 colors HAM8 picture

:-)

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Old 28 October 2016, 22:52   #49
Jack Burton
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OK, thanks Alain !

So to reach ~262144 colors we need a 16M pixels image, which can't be displayed on a standard Amiga. So finally these HAM8 256K colors are nothing more than a theoretical number... I remember having read on the web that the Amiga could display up to 655000 colors, go figure !

Anyway, I downloaded on some landscape pics and rendered them with ImageFX in the HAM8 SuperHiRes modes (normal and laced), and I must admit that the result were very good, sharp and still very colored, so it's OK for me as it is. HAM8 rocks !
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Old 29 October 2016, 01:18   #50
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So to reach ~262144 colors we need a 16M pixels image, which can't be displayed on a standard Amiga. So finally these HAM8 256K colors are nothing more than a theoretical number...
Not really, it's just that your particular test image doesn't cover the RGB range very well when you crop out just a small part of it.
If you're taking the top left 5x5 squares then you're only going to be testing with 25 blue levels out of 256, and some of those will be mapped to the same blue level after colour-reduction to 18-bit, so you'd probably only have 10 unique blue levels out of 64 represented.

Therefore your potential colour range of 262144 colours is reduced to 262144*10/64 = 40960, which is pretty close to the result you got.
If instead of cropping you do a nearest-neighbour scaling on your test image to reduce it to 512x512 pixels, then repeat your test I think you'll get a result much closer to 262144.
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Old 29 October 2016, 06:15   #51
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Ok, I remember seeing plenty of programs back in the day which showed the entire 4096 OCS/ECS colour palette on screen at once. Now, of course, I can't find any. Can anyone help please?
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Old 31 October 2016, 19:49   #52
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Ok, I remember seeing plenty of programs back in the day which showed the entire 4096 OCS/ECS colour palette on screen at once. Now, of course, I can't find any. Can anyone help please?
12 bit RGB ICS/OCS/ECS compliant attached.
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Old 01 November 2016, 18:04   #53
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Hello

@Jack Burton
>the Amiga could display up to 655000 colors, go figure !
Certainly as I think the max number for ham8 is certainly 2097152 colors but my DatatypeToHam prog dont manage the palette smartly enough to go beyond the 262144 colors

> pics and rendered them with ImageFX
you can also use my (Aminet available) DatatypeToHam program for converting your pictures to Ham ...

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Old 02 November 2016, 11:37   #54
Jack Burton
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Not really, it's just that your particular test image doesn't cover the RGB range very well when you crop out just a small part of it.
If you're taking the top left 5x5 squares then you're only going to be testing with 25 blue levels out of 256, and some of those will be mapped to the same blue level after colour-reduction to 18-bit, so you'd probably only have 10 unique blue levels out of 64 represented.

Therefore your potential colour range of 262144 colours is reduced to 262144*10/64 = 40960, which is pretty close to the result you got.
If instead of cropping you do a nearest-neighbour scaling on your test image to reduce it to 512x512 pixels, then repeat your test I think you'll get a result much closer to 262144.
Yes, true, I didn't think about that.
I did some test again, I scaled the image to 512x512 as you advised me, and this time the color counting result was 63526 colors ! It's quite impressive because this time it's 4 times less colors than 262144 (from 24bit 512x512) whereas in my first test (1280x1280 -> 41082) it was 39 times less colors from the 24bit 1280x1280 source !
So you were right, in fact it really depends on the nature of the image displayed. For that matter landscapes give very good results, almost 24bit quality.
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Old 02 November 2016, 11:38   #55
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Hello

@Jack Burton
>the Amiga could display up to 655000 colors, go figure !
Certainly as I think the max number for ham8 is certainly 2097152 colors but my DatatypeToHam prog dont manage the palette smartly enough to go beyond the 262144 colors

> pics and rendered them with ImageFX
you can also use my (Aminet available) DatatypeToHam program for converting your pictures to Ham ...

Alain Thellier
I tried DatatypeToHam. I sent you a PM.
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Old 02 November 2016, 16:05   #56
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Wow, interesting thread. Would be very curious to see the image comparisons of the following formats:
  • HAM6 Interlaced
  • HAM8 Interlaced
  • Sliced-HAM
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Old 02 November 2016, 18:47   #57
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Slightly OT but i can't resist to warm this discussion a bit

Atari STE Medres (640x200) with: software Dynamic CLUT change, software Interlace and software Overscan... - this show how skilled developers are able to bend hardware beyond specification... sad that similar quality is not possible on Amiga - once again



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Old 02 November 2016, 19:09   #58
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sad that similar quality is not possible on Amiga - once again
And why would similar quality not be possible on Amiga?
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Old 02 November 2016, 20:02   #59
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And why would similar quality not be possible on Amiga?
Perhaps lack of sufficiently skilled developers?
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Old 02 November 2016, 20:40   #60
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Perhaps lack of sufficiently skilled developers?
Or maybe rather a lack of interest, getting excited about displaying lots of colors on the Amiga is so 1985
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