Re: PNG? [was Re: ANNC: PortaCello3]

From: Kenny Tilton (ktilton_at_nyc.rr.com)
Date: 04/21/04 

Date: Wed, 21 Apr 2004 03:15:47 GMT

Simon Alexander wrote:

> Kenny Tilton <ktilton@nyc.rr.com> writes:
>
>>Whoa, I just now told ImageMagick to write it out as PNG instead of JPG and
>>it came out five times bigger, twice as big as GIF. Do those numbers sound
>>right? Oh, OK, a BMP comes out five times /bigger/ than the PNG, and I know
>>the GIF is controversial for the compression algorithm.
>
>
> Kenny, you have just discovered the difference between lossless and lossy
> compression. Meaning that lossless compression will encode exactly the same
> image you started with....

I had never heard of PNG, just assumed it was some FSF alternative to
something. I didn't know GIF was lossy, tho. That explains a
long-standing mystery about why PhotoShop would not allow GIF saves of
certain color modes.

>
> JPEG - lossy, with 'quality' parameter
> GIF - lossy, pallete based colour
> PNG - lossless, with 'compression' parameter (just like gzip, higher is
> more compression but will cost more CPU to decompress
> BMP - lossless, no compression, windows standard
>
> Out of all these options, PNG is the best if you care about image fidelity
> more than bandwidth, JPEG is probably best if your priorities are the
> other way around.

Yeah, I'll stick with PNG for screen shots. The Savages of CLIM really
hate my eye-candy, so I want to rub it in as much as possible. :)

I must say, I had been surprised at how bad the JPGs looked, but I never
put two and two together. I have played a lot with JPGs to see what
difference various qualities made and always thought JPG compression was
splendid. Probably it breaks down more noticeably because of the small
type and antialiasing.

Thx for the info.

kenny 

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