W3C home > Mailing lists > Public > www-html@w3.org > February 2000

RE: Netscape and IE images

From: <rev-bob@gotc.com>
Date: 03 Feb 2000 09:47:33 -0500
To: www-html@w3.org
Message-Id: <200002030948810.SM01060@Unknown.>
> ** Original Sender: "Benjamin Randall" <barcop@beld.net>
> Saw your question posted, and I have an answer for you.

Unfortunately, you've got some bad data here.  I work in a prepress environment, so I see 
this sort of thing regularly:

> TIFF and PCX formats are coded for Print, or CMYK (Cyan, Magenta, Yellow, Black),

Commonly, sure - but by no means exclusively.  We deal with RGB-encoded TIFFs every 
day; our HP scanners generate RGB TIFF images, which we then have to convert to CMYK 
- and in doing so, we can tweak the color profile automatically.  Comes in handy.  As for 
PCX, have you ever played Quake 2?  The skins for those models are in PCX format - and 
somehow, I doubt those are intended for print.  ;)

> and JPG and GIF are coded for screen or RGB (Red, Green, Blue).

That's accurate, at least as far as I can attest.

> CMYK is good for print, because it only allows for up to 16+ thousand different colors,
> the maximum capability that printers today, even professional print presses can do.

You're off by a good bit.  CMYK stores eight bits per color - meaning a CMYK image 
stores 32 bits per pixel.  This is quite a bit more than the 24-bit color allowed in RGB.  
(Okay, so maybe I ought to mention that the K channel is pure grayscale, but gray is a color 
just the same....)

> RGB is almost limitless, but, allas its in the millions somewhere where the ammount of
> distiguishable colors it can allow.

You do have one thing right here - RGB's 24-bit depth translates to 16.7 million colors.  
Your assertion that this is more than CMYK can handle, though, is flat wrong.

> JPG and GIF are different though.  While GIF handles solid color, and solid color
> transitions better than JPG (this is why it does well with animations) and has a smaller file
> size, JPG handles, on the pixel level, a smoother transition between similar colors, thus the
> higher file size (usually used for photographs).

Okay, you've got a dangerous amount of misinformation here.  First up, JPGs are usually 
much smaller than GIFs given the same image - because JPG uses a lossy compression 
scheme which allows for really small files for fairly large images.  That lossy compression is 
also why JPG doesn't handle solid colors well; the compression is geared toward images that 
are photos as opposed to simple art. Second, GIF handles animations better than JPG 
because GIF allows for multiple image blocks - saying this is "better" handling is like saying 
that a monitor is better than a piece of cardboard for displaying a web page; JPG just doesn't 
have the tools to handle animation.
> As for BMP, it was actully created by microsoft, and never caught on, due to 2 things, its
> HUGE file size, and its poor image quality, especially with photographs.

A standard BMP is really not much different from an RGB-encoded TIFF - same data, just a 
little different format.  In fact, I think I've seen a few CMYK BMPs.  Thing is, BMP and 
TIFF are typically *uncompressed* formats (although there are compressed versions out 
there), which is why they're so big in comparison to GIF/JPG.

Of course, one file format is conspicuous in its absence here: PNG.  IMO, it's best explained 
by comparison to the other formats here, which makes for a nice little summary/wrapup:

RGB encoding: GIF, JPG, TIFF, BMP, and PNG.
CMYK encoding: TIFF, BMP (?), and PNG.
Palette-based color encoding: PNG (optional), GIF (mandatory).
True animation (multiple frames): GIF and PNG, but not TIFF, BMP, or JPG.
Lossless data storage: All but JPG.
High color range: All but GIF, which is limited to 256 different colors at most.
Simple transparency (one color): GIF and PNG only.
Complex transparency (shades): Multi-channel PNG only, map stored in alpha channel.
Smallest image size (complex image): JPG.
Largest image size (any image): TIFF/BMP.
Endorsed for Web use: JPG, PNG, GIF (discouraged in favor of PNG).
Safe for open Web use: JPG, GIF.  (Old browsers don't support PNG, most current ones 

Have I missed anything?

 Rev. Robert L. Hood  | http://rev-bob.gotc.com/
  Get Off The Cross!  | http://www.gotc.com/
Received on Thursday, 3 February 2000 09:46:52 UTC

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