Graphic Formats

Hello Experts:  What are the relative advantages and possibly disadvantages for the many different graphics file formats?  As an experiment, I just took a screen shot of part of a web page- nothing unusual about the visual characteristics or graphics contents- just a partial screen shot of a Face Book web page.  I then saved it over and over again, each time in a different file format.  They were: .bmp, .gif, .jpg, .pcx, .png, .tga, .tif, .pdf and two flavors of .webp: one at "100% quality" whatever that meant, and the other at "lossless."  I used IrfanView for some of the saves, as that had more formats to choose from. I noticed that IrfanView has an additional 13 formats that I could have saved in.  The app warned that saving a .webp file at lossless would be- to quote -"Slow!"  They weren't kidding.  It  must have taken a full 10 seconds for the file to save.  I have file sizes ranging from 135 KB for .gif, all the way up to 2,321 KB for .bmp.  I can see only tiny differences in the images when comparing one to the next- with the exception of some big changes in a part of the image that consists of splotches of color.  Boxes with solid color change very little, and other parts of the image change hardly at all when clicking from one to the next.  My question is: why would any particular format be preferred for something over another, when the image differences are for the most part so slight?  And why would .bmp be used for much, when the file size 4 to 17 times the size of the various other formats?  As usual, thanks in advance for your help.

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Dave BaldwinFixer of ProblemsCommented:
.bmp, .gif, .jpg, .pcx, .tga, and .tif were proprietary formats for different programs before the internet became common.  .png was created expressly to get around copyright and patent problems in both .gif and .jpg formats.  The copyrights and/or patent problems have since been resolved.  .gif is a more limited format than .jpg except that .gif can have transparency and .jpg can't.  And .png can do anything either one of them can do.

.pdf is not a graphic format but a document format that can contain both images and text including embedded fonts.  'Save to PDF' is probably saving the image in JPG format internally.

There are a lot of other formats that were/are proprietary for certain programs.  You can look all these formats up in Wikipedia to see what their characteristics are.
Dave BaldwinFixer of ProblemsCommented:
Here are some links.  Note that most of these date from the 1980's or earlier.  Note also that most of these are not just a single format but a range of formats.

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In short:


use mostly RAW (full data, no compression), later when editing, they can bring a lot of
details back from shadows or dark areas, during editing.
JPG, usually low compression to retain as much information possible while not degrading the quality of the picture. Later editing will not bring out "lost" detail from the shadows, because the important data from the RAW stage has been compressed and lost.

JPG, usually slightly higher compression rate, the make the pictures smaller in size.
PNG, lossless, supports transperancy, favored by more and more web developers
GIF, 256 color palette, supports sequence, favored for a quick way to show and repeat funny "movies" (the 256 colors will result in the visible graininess)

Mostly non-used:
TIF, usually black/white, mostly used to store faxes.
BMP, lossless, results in big files.
ChristopherNlsAuthor Commented:
Excellent and informative answers, both.  Just what I was looking for.  Thanks, Experts.

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Photos / Graphics Software

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