Hi-DPI and bitmaps (was Re: Large progress indicators in Leopard)

FROM : Chris Hanson
DATE : Sat Nov 24 07:30:07 2007

On Nov 23, 2007, at 1:41 PM, Ricky Sharp wrote:

> As John pointing out, the control could have been already modified 
> to support Hi-DPI (aka resolution independence).  My guess is that 
> Apple is using bitmapped images and are just providing multi-res 
> flavors (72 dpi and 288 dpi).
>
> But, IMO, that's bad!  If I were implementing the control, I would 
> allow any size and would either vector-based images (e.g. PDF) or 
> drawing primitives for the content.


Really, whether a control supports high DPI and whether it is 
implemented using vectors/primitives or using bitmaps is largely 
irrelevant.  A bitmap sized for 72 DPI can serve just fine for higher 
resolutions, as if the *interface* is running at a higher resolution 
it will still be appropriately sized.

One thing to think about is how newspapers and magazines do it.  In 
publishing, the "line work" plate files -- black & white text, 
typically -- are typically high-resolution, 1200 to 2400 DPI depending 
on the medium.  The "continuous tone" plate files -- photographs, 
charts, etc. -- are however typically 75 DPI to 300 DPI depending on 
the medium.

This is partly because rasterizing color images in print involves 
halftone patterns, and you don't need a 2400 DPI color image to 
generate a 2400 DPI color halftone.  (In fact, you really don't want 
one.)  On the other hand, you also often don't need as high a 
resolution continuous-tone color image as you think you need to get 
the effect you're looking for.

The reason some software doesn't look so great when run at 200% 
scaling is not because it uses bitmapped art, but because it's running 
at 200% scaling on a 72-110 DPI screen.  If it were running at 100% on 
a 144-220 DPI display, it would likely look pretty decent as the 
"chunkiness" wouldn't be any more apparent than it is on current 
displays.

So, don't automatically assume that using bitmaps is bad for hi-DPI 
controls.  It's not always great, but it's not automatically a fail. 
Try printing your images at half scale on a high-resolution printer 
and see how they look first...

  -- Chris