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Article: <5fa3k8$jj4@sjx-ixn6.ix.netcom.com>
From: saquo@ix.netcom.com(Nancy )
Subject: Re: Tholen Caught DOCTORING Hale-Bopp Images!
Date: 1 Mar 1997 20:30:00 GMT
In article <3316682A.4B08@acs.tamu.edu> Eric Kline
writes:
>> Dave, I went to your web site at ..
>> http://www.ifa.hawaii.edu/images/hale-bopp/tholen-sep1/
>> hb_ufo_tholen.html
>>
>> I downloaded a red, green, and blue named
>> ccd024_02.jpg, ccd025_02.jpg, and ccd026_02.jpg.
>> The whole area called Hale-Bopp was so bright that I
couldn't
>> make anything out, like a Sun in the center of the JPG.
>>
>> Going back to see if selecting another set would allow
better
>> analysis, I noticed an odd thing. When the page is first
>> coming in, these little thumbnails show DIFFERENT
>> STAGES of images, as though there were several overlays
>> coming in, each making certain areas brighter, etc. At
first,
>> the area where Hale-Bopp is supposed to be is almost
black,
>> but the stars in the plate are bright. Then the center
part
>> gets rapidly brighter, in successive passes.
>>
>> What's going on there? Is the image in fact SEVERAL
>> images, being overlaid? How come the background stars
>> don't increase in brightness, just the center part, as
this is
>> going on?
>> saquo@ix.netcom.com (Nancy)
>
> I'm taking a guess here, but are you using Netscape? You've
> described how Netscape loads images. No big mystery here.
> eric kline <emk9267@acs.tamu.edu>
In article <5f7ujq$m2s@news.Hawaii.Edu> David Tholen
writes:
> There is only one "overlay". Some web browsers
build up
> images, starting at lower resolution (obvious pixel
structure)
> to higher resolution, which might possibly create an
illusion.
> tholen@galileo.ifa.hawaii.edu
I neglected to mention that the images that show this odd behaviour are GIFs, gifs made into thumbnails for the selection page. Gifs have the option of loading top down, line by line filling in, or interlaced fill in which gives a blocky appearance which is unmistakeable. Gifs also have the ability to be a series of pages, a facility often used to produce animated graphics that page through the gif. Gif also have the ability to have their color codes indicate that a certain color is to be considered a transparency, showing any colors on a graphic underneath, should there be such a graphic on the web page beneath.
| 1. | This thumbnail gif from David Tholen is not showing Hale-Bopp as a dark place due to the way Netscape is loading the image. I picked the gifs out of the Netscape catche, after having stopped Netscape during the download of them, and they appear as perfect graphics as is, with the area where Hale-Bopp is essentially BLACK in the sky surrounded by bright stars! |
| 2. | Checking out these thumbnail gifs in Hijack I find they are NOT ENCODED AS INTERLACED, and didn't expect that I would. Interlaced gifs load in with a characteristic blocky look, as the gif is encoded with instructions to load by skipping lines, and going back in repeated passes to fill in the lines. A careful inspection of these partial thumbnail gifs, which have a lot of grayscale as well as black and white, shows that NO lines are skipped, nor are the lines duplicated. |
| 3. | Hijack does not report the gifs I retrieved from my Netscape catche as having more than one page, although there is a possibility that the full thumbnail WOULD have more than one page, but no animation was apparent on the selection web page where the thumbnails presented. Paging is a replacment, anyway, and this was more like a fill-in, where Hale-Bopp entered the picture AFTER the normal skyscape was popped up. |
| 4. | What you are suggesting, that high resolution and low resolution is treated differently by a browser, is nonsense. A gif is encoded with color codes, line by line, and browsers act like dummies, following instructions encoded in the graphic. No doubt the gif presents to the browser saying "I'm this wide and high, here's my color codes, I'm interlaced so am presenting the lines numbered for placment, I have x pages that are to repage x times at x speed for an animation." And no doubt the gif presents the lines to the browser saying "I'm line 1, go x pixtels with white, then put y pixtels of black, then go z pixtels of gray". |