Apple IIgs largest raster

[vol]

I am curious about the controversy surrounding the IIgs graphic modes.  Most sources claim that the IIgs maximum raster is 640x200 but there is also information that it is 640x400, for example, this page and this.  Would anyone like to help find the truth?

Edited December 17, 2023 by vol

[potatohead]

640x400 would require either an interlaced display (no way Apple would do that), or a VGA type horizontal sweep.

 

Neither are in the GS.

 

The raster is 640x200

[Iamgroot]

Those are typos.  3200 colors can only be displayed in 320 mode.  640 mode is only 4 color, but colors can be dithered to 16 colors, and there is no ability to produce more than 200 lines in 640 mode.

 

Kegs now supports the VOC card which can display 320x400 interlaced.  But 3200 colors is very processor intensive and can only be viewed on the 320x200 screen.

 

But technically speaking, there is no liimit to the size of graphics file.  With the correct software, pictures of up to 4096 x 4096 can be displayed.  But I don't even know why it is limited to that since moving the cursor to display the next area of a graphic wouldn't be hindered in any way.  The max file size is 16 Mb, meaning one should be able to get about 900 (320x200) screen-sized chunks in one file.  Meaning a file could potentially hold up to 30 screens wide and 30 screens high.  The max graphic size then would be roughly 9600x6000 pixels.

 

Edit:  I just remembered, the 4096 x 4096 limit is part of QuickDraw routines, which can be bypassed to view larger screens.

Edited December 18, 2023 by Iamgroot

[vol]

Thank you very much.  Can anyone help me a little more?  I want to get a color photo on the IIgs.  It seems tohgr does what I need.  But it just doesn't seem to work with the -3200 option for my pictures. I tried different images and I always failed to get a proper conversion. It seems that the utility requires somehow preprocessed images and I don't know what should be preprocessed.  I surfed the net about the tohdr peculiarities for the -3200 mode but I found nothing. 
Maybe there are other options besides tohgr to get 3200 colors?

[Iamgroot]

What do you mean by proper conversion?  How are you viewing the final result?

 

You can only view a3200 color picture on a IIGS and only with the software meant to view 3200 colors.  A standard super-hires-viewer will only use the first palette of the picture.  It won't look right on the machine you are running tohgr from or even on a IIGS unless you have a 3200 color viewing program.

[potatohead]

What is the VOC card?

[nick3092]

11 hours ago, potatohead said:

What is the VOC card?

Video Overlay Card

[vol]

14 hours ago, Iamgroot said:

What do you mean by proper conversion?  How are you viewing the final result?

 

You can only view a3200 color picture on a IIGS and only with the software meant to view 3200 colors.  A standard super-hires-viewer will only use the first palette of the picture.  It won't look right on the machine you are running tohgr from or even on a IIGS unless you have a 3200 color viewing program.

The tohgr converter produces a preview file in the png-format so it is quite easy to check the result.  I haven't still tried the tohgr results on a IIgs.  However is it true that there is no a viewer?!  I can only hope that if I put the image file content at $C0000 it will do the trick.

I have an assumption that tohgr doesn't work if the source image has more than 16 different colors in a line.

Edited December 19, 2023 by vol

[Duhast]

Resize the picture to something reasonable for the //gs, and then Convert3200 or SHRconvert are your friends.  SHRview is also nice for viewing large pictures as you can "scroll" around the screen.

[Iamgroot]

I wouldn't bother with 3200 color conversion as it is kind of a misnomer.  The IIGS can only display 16 colors per line no matter what graphics is used.  Pretty much all the time, a graphics will look just as good with 256 colors.  Just reduce your graphics size down to 320x200 and transfer that over to the IIGS in .png, .bmp or .tif format.  SHRConvert does a pretty decent job to convert to 16 or 256 colors.

[vol]

Let me report a few things:
   1) Super Convert 4 (formerly SHRCONVERT) works rather very poorly for photos.  It can only give some quality when it uses 16 colors per image.  Its multi-palette conversion quality is just very bad.
   2) Convert 3200 works much better for photos.  It can actually use several hundred colors per image!  However the IIgs power can't support complex extensive search algos.  So IMHO a cross-platform converter can make better quality.
   3) Cross-platform tool TOHDR often doesn't just work for unknown reasons.  It's sad that the community didn't test this great utility thoroughly and didn't give proper feedback to the author.
I have attached the original image and the best conversion result to this post.  It would be great if somebody could get a better conversion result.

On 12/19/2023 at 6:50 PM, Iamgroot said:

I wouldn't bother with 3200 color conversion as it is kind of a misnomer.  The IIGS can only display 16 colors per line no matter what graphics is used.  Pretty much all the time, a graphics will look just as good with 256 colors.

It sounds just rather oddly to me.  The Apple IIgs can actually show 3200 colors on an image.  So it is not clear why someone would call this a misnomer.

Edited December 22, 2023 by vol

[Iamgroot]

The misnomer is that the number of colors is not 3200 on the screen.  Many of the palettes use the same colors.  And the bottom line is that the IIGS can still only view 16 colors per scanline.  That is why you get banding, like on the girls forehead, flower and teapot.  Usually 3200 conversions are worse than a 16 palette dither.  And it will also take 100% of the cpu power to view a 3200 picture.  Very hard to do anything with it.  And the compressed file size is also much larger, for the extra effort for very little extra quality.  Not realistic when working on a IIGS.  But each to his own.

 

As per photos, for me dark photos look better in grayscale than have a few bright colors against a dark background.  I captured your top photo and converted it to 256-color grayscale, then used the multi-palette conversion using SuperConvert.  Also used a graphic convertor to reduce the colors to 32, then used SuperConvert multi-palette mode.  Here are the results.

 

 

 

 

Edited December 23, 2023 by Iamgroot

[vol]

On 12/23/2023 at 8:38 PM, Iamgroot said:

The misnomer is that the number of colors is not 3200 on the screen.

You can display a gamut that shows exactly 3200 colors on your GS.

On 12/23/2023 at 8:38 PM, Iamgroot said:

Usually 3200 conversions are worse than a 16 palette dither. 

I can't agree.  The problem is in the quality of the converters. Super Convert works just very badly for this.  3200 Convert is much better but it is far from perfect.  I can repeat that this type of conversion requires a lot of CPU power that the IIgs can't provide.  I remember that an image converter for the Amiga can work tens minutes on a modern PC!
I can confirm my words with examples on the page - Super Hires conversions are much better than dithering on the Double Hires pictures.  The image of the Alps there contains 253 colors.  And I can again express my sadness that this great tool was not developed further.  
My picture for the IIgs contains 112 colors and IMHO it looks much more colorful that your dithering.  Dithering is available in 3200 color mode too.  

On 12/23/2023 at 8:38 PM, Iamgroot said:

And it will also take 100% of the cpu power to view a 3200 picture.

I know nothing about this.  It seems rather implausible for me.  Could you provide a link to some material that confirms this?  IMHO the video can stop the CPU when it reads the palette information each visible line but the CPU is free on the overscan area so we must have at least 30% of the CPU power for this mode.  It is not too much but it is still faster than the IIc.

Edited December 25, 2023 by vol

[Iamgroot]

https://groups.google.com/g/comp.sys.apple2/c/Wvt80cc4tp8/m/VpU8Ekls4SEJ