EHB, HAM6 and HAM8 demonstration pictures?

TroyWilkins · 19 October 2016, 05:20

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?

TroyWilkins · 19 October 2016, 07:51

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.

mihcael · 19 October 2016, 08:01

AGA HAM8 should be barley distinguishable in quality to the original at that size.

TroyWilkins · 19 October 2016, 08:03

Well it looks pretty good to me

ajk · 19 October 2016, 08:04

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.

TroyWilkins · 19 October 2016, 08:08

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?

thomas · 19 October 2016, 08:36

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.

TroyWilkins · 19 October 2016, 08:36

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

TroyWilkins · 19 October 2016, 08:38

Quote:

Originally Posted by thomas

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.

thomas · 19 October 2016, 08:44

Quote:

Originally Posted by TroyWilkins

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.

TroyWilkins · 19 October 2016, 08:49

Quote:

Originally Posted by thomas

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

TroyWilkins · 19 October 2016, 09:05

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

ajk · 19 October 2016, 09:10

Yes, those would be a pretty good demonstration of how a photograph can be displayed on an OCS and AGA Amiga.

mihcael · 19 October 2016, 09:19

Quote:

Originally Posted by TroyWilkins

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.

TroyWilkins · 19 October 2016, 09:24

Quote:

Originally Posted by mihcael

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.

thellier · 19 October 2016, 09:49

There is my prog for converting to ham6/ham8 to a good quality
http://aminet.net/package/gfx/conv/DatatypeToHam

Alain Thellier

TroyWilkins · 19 October 2016, 10:07

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!

Minuous · 19 October 2016, 15:54

The claim on that page that HAM8 only supports 262144 colours is incorrect.

Thorham · 19 October 2016, 16:14

Quote:

Originally Posted by Minuous

The claim on that page that HAM8 only supports 262144 colours is incorrect.

Indeed

khph_re · 19 October 2016, 21:56

there is also sliced ham on OCS i think? as well as overscan and interlace to increase the resolution.

19 October 2016, 05:20	#1
TroyWilkins Registered User Join Date: Jan 2015 Location: Melbourne, Australia Posts: 548	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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19 October 2016, 07:51	#2
TroyWilkins Registered User Join Date: Jan 2015 Location: Melbourne, Australia Posts: 548	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.

19 October 2016, 08:01	#3
mihcael Zone Friend Join Date: Jan 2006 Location: Aussie Posts: 1,144	AGA HAM8 should be barley distinguishable in quality to the original at that size.

19 October 2016, 08:03	#4
TroyWilkins Registered User Join Date: Jan 2015 Location: Melbourne, Australia Posts: 548	Well it looks pretty good to me

19 October 2016, 08:04	#5
ajk Registered User Join Date: May 2010 Location: Helsinki, Finland Posts: 1,341	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.

19 October 2016, 08:08	#6
TroyWilkins Registered User Join Date: Jan 2015 Location: Melbourne, Australia Posts: 548	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?

19 October 2016, 08:36	#7
thomas Registered User Join Date: Jan 2002 Location: Germany Posts: 7,002	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.

19 October 2016, 09:05	#12
TroyWilkins Registered User Join Date: Jan 2015 Location: Melbourne, Australia Posts: 548	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

19 October 2016, 09:10	#13
ajk Registered User Join Date: May 2010 Location: Helsinki, Finland Posts: 1,341	Yes, those would be a pretty good demonstration of how a photograph can be displayed on an OCS and AGA Amiga.

19 October 2016, 09:49	#16
thellier Registered User Join Date: Sep 2011 Location: Paris/France Posts: 274	There is my prog for converting to ham6/ham8 to a good quality http://aminet.net/package/gfx/conv/DatatypeToHam Alain Thellier

19 October 2016, 10:07	#17
TroyWilkins Registered User Join Date: Jan 2015 Location: Melbourne, Australia Posts: 548	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!

19 October 2016, 15:54	#18
Minuous Coder/webmaster/gamer Join Date: Oct 2001 Location: Canberra/Australia Posts: 2,642	The claim on that page that HAM8 only supports 262144 colours is incorrect.

19 October 2016, 21:56	#20
khph_re Registered User Join Date: Feb 2008 Location: Northampton/UK Posts: 525	there is also sliced ham on OCS i think? as well as overscan and interlace to increase the resolution.

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