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Old 19 October 2016, 06:20   #1
TroyWilkins
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EHB, HAM6 and HAM8 demonstration pictures?

Hi everyone.

I'm trying to find examples of pictures to use to demonstrate the differences between the different capabilities of the various Amiga models display output for my web site.

My aim is to have an original 24-bit picture, and then convert that to the best that could be displayed in each mode. So say 640x400 Ham8, 640x400 256 colour, 320x200 Ham6, 320x200 EHB, etc. I'm choosing 400 and 200 as those were possible on NTSC and PAL amigas.

It seems to me that the best way to do this and have it look accurate, would be to use WinUAE to utilise the 'Save screenshot' option within Host-> Output, and to use say Photogenics or ImageFX to load the original picture and save it out as a Amiga file in the required screenmode, then view the picture, tkae a screenshot, and then crop that screenshot as needed.

Does anyone have any better ideas?

Does anyone have any good images to use for this, or should I just go and take some photos myself to use?
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Old 19 October 2016, 08:51   #2
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Here's my effort, from a picture I took in my own backyard:


The original (reduced in resolution to 468x400)


AGA HAM8


OCS/ECS HAM


AGA 256 colour


OCS/ECS EHB

And yes, I know, I should have reduced the resolution further, but I wanted to not have them all postage stamp sized on a modern display device, without doubling their size. The intention is to show the colour depth differences, hence choosing an original image with the many shades of blue in the sky.

Any feedback would be very much appreciated.
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Old 19 October 2016, 09:01   #3
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AGA HAM8 should be barley distinguishable in quality to the original at that size.
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Old 19 October 2016, 09:03   #4
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Well it looks pretty good to me
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Old 19 October 2016, 09:04   #5
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With proper dithering the banding that you get (in the sky, especially) could be mitigated a lot. For example Personal Paint can do a really good job of reducing a full-colour image down to 256 (or less). I'm however not sure how well it deals with HAM images, I never really used them much.

HAM modes are somewhat special in how they work, so any converter needs to be crafted with the limitations in mind. There have been discussions here on the forum regarding the best algorithm for the job. See here, for example.
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Old 19 October 2016, 09:08   #6
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Agreed, I was torn as to if I should use dithering, given that the OCS/ECS images are in a higher resolution than would usually be used, which could lead to an impression that it's a better picture than it really is - unless I halve the resolution before converting to the correct display mode and then double the size of the picture? What do we think? Or should I do that for ALL the pictures?
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Old 19 October 2016, 09:36   #7
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OCS cannot do hires with more than 4 bitplanes, so HAM is not possible in this resolution. For HAM6 you should therefore reduce the horizontal resolution to 320 (and then double each pixel to get the aspect ratio back).

Likewise it cannot do 400 lines without interlace.

Conclusion is that to display a HAM or EHB image without flicker on an A500 or A2000 you should reduce the resolution to 320x200.
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Old 19 October 2016, 09:36   #8
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How about these? I've dropped the resolution for all the Amiga images and added Floyd dithering, images are being processed in ImageFX 1.5


Original (double x and y resolution of the Amiga images below).


HAM8


HAM


256 Colour

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Old 19 October 2016, 09:38   #9
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Quote:
Originally Posted by thomas View Post
OCS cannot do hires with more than 4 bitplanes, so HAM is not possible in this resolution. For HAM6 you should therefore reduce the horizontal resolution to 320 (and then double each pixel to get the aspect ratio back).

Likewise it cannot do 400 lines without interlace.

Conclusion is that to display a HAM or EHB image without flicker on an A500 or A2000 you should reduce the resolution to 320x200.
Yeah, I've now done that and added dithering, all Amiga images are now in low resolution modes.
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Old 19 October 2016, 09:44   #10
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Quote:
Originally Posted by TroyWilkins View Post
all Amiga images are now in low resolution modes.
That's not the right way, either. An A1200 or A4000 can indeed output 640x400 with 8 bitplanes without flicker.

And with a properly choosen palette you could even remove the compression artifacts appearing on the wall on the right of the HAM8 image in your fist post.
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Old 19 October 2016, 09:49   #11
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Quote:
Originally Posted by thomas View Post
That's not the right way, either. An A1200 or A4000 can indeed output 640x400 with 8 bitplanes without flicker.
Indeed, the aim is to show the display differences, although you do have a good point, perhaps the AGA images should remain in the source resolution, although to be fair, on a 15khz screen, in interlaced mode they'd flicker badly, and I don't think I can easily simulate that, nor do I really want to, hahaha
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Old 19 October 2016, 10:05   #12
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Is this a better representation of the video output capabilities and differences between OCS/ECS and AGA?


Original.


High resolution interlaced HAM8


HAM


High resolution interlaced 256 Colour


EHB
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Old 19 October 2016, 10:10   #13
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Yes, those would be a pretty good demonstration of how a photograph can be displayed on an OCS and AGA Amiga.
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Old 19 October 2016, 10:19   #14
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Quote:
Originally Posted by TroyWilkins View Post
Is this a better representation of the video output capabilities and differences between OCS/ECS and AGA?
I still think the Ham8 image is not a realistic representation of what is possible.

I will try to show you.
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Old 19 October 2016, 10:24   #15
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Quote:
Originally Posted by mihcael View Post
I still think the Ham8 image is not a realistic representation of what is possible.

I will try to show you.
It may not be, but to get that I have used WinUAE setup as an A1200, used ImageFX 1.5 to load the original JPG, then set it to render on screen as HAM8 in hires interlaced, then taken a snapshot of the screen using WinUAE. Same for all the other screen captures, using appropriate display options, only for the OCS/ECS images I halved the resolution and chose the Amiga1.3 render module, before choosing HAM or EHB - both in low res.




Last edited by TroyWilkins; 19 October 2016 at 10:30.
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Old 19 October 2016, 10:49   #16
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There is my prog for converting to ham6/ham8 to a good quality
http://aminet.net/package/gfx/conv/DatatypeToHam

Alain Thellier
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Old 19 October 2016, 11:07   #17
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This is what it's all for, and before you go looking at the other pages there, I still have a LOT of work to do, so many pages only have placeholder pages, if anything, and others have a lot more work to do: http://theamigamuseum.com/the-hardware/the-aga-chipset/

Thank you everyone for your input!
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Old 19 October 2016, 16:54   #18
Minuous
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The claim on that page that HAM8 only supports 262144 colours is incorrect.
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Old 19 October 2016, 17:14   #19
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Quote:
Originally Posted by Minuous View Post
The claim on that page that HAM8 only supports 262144 colours is incorrect.
Indeed
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Old 19 October 2016, 22:56   #20
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there is also sliced ham on OCS i think? as well as overscan and interlace to increase the resolution.
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