greg
On Dec 24, 2003, at 12:30 AM, Roger Johnstone wrote:
On Wednesday, December 24, 2003, at 06:21 PM, Greg Koelpien wrote:
I am perplexed by an issue with Mac OS 8.1's "Desktop Picture" control panel on my modded Color Classic. The problem is that I can have a perfectly smooth image scaled at 640x480 that looks great in Photoshop. However, when I set it as the background image, it looks a lot worse, and there's this weird banding effect. I've tried high quality JPG, 256-color GIF, PICT files, and it still looks bad. The screen resolution of 640x480 with thousands of colors should render these perfectly. These same images look fine when opened in Photoshop 4 on the same machine. Any explanation as to why these images don't look their best as background images but fine in PS?
Greg Koelpien
I used to have the exact same problem with an iMac running 8.1! It too was running in 16-bit colour mode. I came to the conclusion that the Destop Picture control panel just reduced the colours in the picture from 24-bit to 16-bit with no attempt at dithering, which caused the banding. When viewing the picture in other programs, they did a decent job of reducing the colours and the pictures looked fine.
It's been a few years, so I can't remember exactly how I solved the problem. Later I got the video RAM upgrade which let me use 24-bit colour, so maybe I didn't solve it! Something to try (if you haven't already), is to open the picture in Photoshop and reduce the colours to 16-bits. Then save the picture as a TIFF or PICT. If you save in JPEG format it will convert it back to 24-bit colour since JPEG only supports 8-bit grey and 24-bit colour, although it shouldn't "undo" the dithering.
-- Roger Johnstone, Invercargill, New Zealand
PS/2 Mouse Adapter for vintage Apple II or Mac order at http://vintageware.orcon.net.nz
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