Computer Novice

[Jean Jeanie]

Ididn't use my computer very much before I started on my family tree. I mainly used it for finding out info from the net.

Now I am using it all the time. However I do get a bit befuddled from time to time. Anyone care to help me?

When I have sent documents to people, I scan them in and save as jpg. and then send them.

Today I have received some docs from a fellow researcher and they are in the following formats:- tif, png. I have also seen bmp. at some point.

What are all these different formats and when should you use them?

Jean

[mesklin]

Jean

Picture formats.
BMP = bitmap. The basic picture format. Anything from 1 to 32 bits per pixel, depending on number of colours (and extras!). If, for example, your picture was 1000x1000 pixels, then file size for 24 bit colour (16 million colours) would be 24x1000x1000 bits or 3Megabyte (8 bits per byte). Not normally compressed.

TIF = very similar to BMP, except that the file is often compressed to make it smaller. Actual size depends on how much you can shrink it mathematically.

PNG = (according to my son, anyway) the future of Internet graphics. A very versatile file format designed for internet use, but usable almost anywhere. Compressible to small sizes, lots of extra features to enable animation, transparency, resizing, quick loading. So good that many IP sites and browsers won't work with it.

GIF = The forerunner of PNG. Designed for internet. Quick loading, small files. Limited (256) range of colours chosen from a large pallette (64,000) of colours.

JPG = Very small files. Loss of detail. Great for colour pictures. Absolutely dreadful if you want a detailed black and white picture.

Hope this helps.

Mesklin

[DavidWW]

A visit to www.scantips.com , www.scantips.com/basics09.html , and exploring that site will provide answers for both newbies and the more advanced!

I'd intended to reference the area on this site that provided the following info, in particular in relation to file compression techniques, but I can't find it, so repeat the previously downloaded info here ..............

TIFF - Tag Image File Format
===================

(.TIF file extension, pronounced Tiff) TIFF is the format of choice for archiving important images. TIFF is THE leading commercial and professional image standard. TIFF is the most universal and most widely supported format across all platforms, Mac, Windows, Unix. Data up to 48 bits is supported.

TIFF supports most color spaces, RGB, CMYK, YCbCr, etc. TIFF is a flexible format with many options. The data contains tags to declare what type of data follows. New types are easy to invent, and this versatility can cause incompatibly, but about any program anywhere will handle the standard TIFF types that we might encounter. TIFF can store data with bytes in either PC or Mac order (Intel or Motorola CPU chips differ in this way). This choice improves efficiency (speed), but all major programs today can read TIFF either way, and TIFF files can be exchanged without problem.

Several compression formats are used with TIF. TIF with G3 compression is the universal standard for fax and multi-page line art documents.
TIFF image files optionally use LZW lossless compression. Lossless means there is no quality loss due to compression. Lossless guarantees that you can always read back exactly what you thought you saved, bit-for-bit identical, without data corruption. This is very critical factor for archiving master copies of important images. Most image compression formats are lossless, with JPG and Kodak PhotoCD PCD files being the main exceptions.

Compression works by recognizing repeated identical strings in the data, and replacing the many instances with one instance, in a way that allows unambiguous decoding without loss. This is fairly intensive work, and any compression method makes files slower to save or open.

LZW is most effective when compressing solid indexed colors (graphics), and is less effective for 24 bit continuous photo images. Featureless areas compress better than detailed areas. LZW is more effective for grayscale images than color. It is often hardly effective at all for 48 bit images (VueScan 48 bit TIF LZW is an exception to this, using an efficient data type that not all others use ).

LZW is Lempel-Ziv-Welch, named for Israeli researchers Abraham Lempel and Jacob Zif who published IEEE papers in 1977 and 1978 (now called LZ77 and LZ78) which were the basis for most later work in compression. Terry Welch built on this, and published and patented a compression technique that is called LZW now. This is the 1984 Unisys patent (now Sperry) involved in TIF LZW and GIF (and V.42bis for modems). It expires in 2003. There was much controversy about a royalty for LZW for GIF, but royalty was always paid for LZW for TIF files and for v.42bis modems.

Image programs of any stature will provide LZW, but simple or free programs often do not pay LZW patent royalty to provide LZW, and then its absence can cause an incompatibility for compressed files.
It is not necessary to say much about TIF. It works, it's important, it's great, it's practical, it's the standard universal format for high quality images, it simply does the best job the best way. Give TIF very major consideration, both for photos and documents, especially for archiving anything where quality is important.

But TIF files for photo images are generally pretty large. Uncompressed TIFF files are about the same size in bytes as the image size in memory. Regardless of the novice view, this size is a plus, not a disadvantage. Large means lots of detail, and it's a good thing. 24 bit RGB image data is 3 bytes per pixel. That is simply how large the image data is, and TIF LZW stores it with recoverable full quality in a lossless format (and again, that's a good thing). $200 today buys BOTH a 60 GB 7200 RPM disk and 512 MB of memory so it is quite easy to plan for and deal with the size.
There are situations for less serious purposes when the full quality may not always be important or necessary. JPEG files are much smaller, and are suitable for non-archival purposes, like photos for read-only email and web page use, when small file size may be more important than maximum quality. JPG has its important uses, but be aware of the large price in quality that you must pay for the small size of JPG, it is not without cost.

PNG - Portable Network Graphics
=====================

(.PNG file extension, the pronunciation 'Ping' is specifically mentioned in the PNG Specification). PNG needs to be mentioned. PNG is not the number one file format, but you will want to know about it. PNG is not so popular yet, but it's appeal is growing as people discover what it can do.
PNG was designed recently, with the experience advantage of knowing all that went before. The original purpose of PNG was to be a royalty-free GIF and LZW replacement (see LZW next page). However PNG supports a large set of technical features, including superior lossless compression from LZ77. Compression in PNG is called the ZIP method, and is like the 'deflate" method in PKZIP (and is royalty free).

But the big deal is that PNG incorporates special preprocessing filters that can greatly improve the lossless compression efficiency, especially for typical gradient data found in 24 bit photographic images. This filter preprocessing causes PNG to be a little slower than other formats when reading or writing the file (but all types of compression require processing time).

Photoshop 7 and Elements 2.0 correct this now, but earlier Adobe versions did not store or read the ppi number to scale print size in PNG files (Adobe previously treated PNG like GIF in this respect, indicated 72 ppi regardless). The ppi number never matters on the video screen or web, but it was a serious usability flaw for printing purposes. Without that stored ppi number, we must scale the image again every time we print it. If we understand this, it should be no big deal, and at home, we probably automatically do that anyway (digital cameras do the same thing with their JPG files). But sending a potentially unsized image to a commercial printer is a mistake, and so TIF files should be used in that regard.
Most other programs do store and use the correct scaled resolution value in PNG files. PNG stores resolution internally as pixels per meter, so when calculating back to pixels per inch, some programs may show excessive decimal digits, perhaps 299.999 ppi instead of 300 ppi (no big deal).
PNG has additional unique features, like an Alpha channel for a variable transparency mask (any RGB or Grayscale pixel can be say 79% transparent and other pixels may individually have other transparency values). If indexed color, palette values may have similar variable transparency values. PNG files may also contain an embedded Gamma value so the image brightness can be viewed properly on both Windows and Macintosh screens. These should be wonderful features, but in many cases these extra features are not implemented properly (if at all) in many programs, and so these unique features must be ignored for web pages. However, this does not interfere with using the standard features, specifically for the effective and lossless compression.
Netscape 4.04 and MS IE 4.0 browsers added support for PNG files on web pages, not to replace JPG, but to replace GIF for graphics. For non-web and non-graphic use, PNG would compete with TIF. Most image programs support PNG, so basic compatibility is not an issue. You may really like PNG.

PNG may be of great interest, because it's lossless compression is well suited for master copy data, and because PNG is a noticeably smaller file than LZW TIF. Perhaps about 25% smaller than TIF LZW for 24 bit files, and perhaps about 10% to 30% smaller than GIF files for indexed data.
Different images will have varying compression sizes, but PNG is an excellent replacement for GIF and 24 bit TIFF LZW files. PNG does define 48 bit files, but I don't know of any programs that support 48 bit PNG (not too many support 48 bit in any form).
Here are some representative file sizes for a 9.9 megabyte 1943x1702 24-bit RGB color image:
File type File size
TIFF 9.9 megs
TIFF LZW 8.4 megs
PNG 6.5 megs
JPG 1.0 megs (1.0 / 9.9) is 10% file size
BMP 9.9 megs
Seems to me that PNG is an excellent replacement for TIFF too.
More PNG info at www.libpng.org/pub/png.

JPEG - Joint Photographic Experts Group
==========================

(.JPG file extension, pronounced Jay Peg). This is the right format for those photo images which must be very small files, for example, for web sites or for email. The JPG file is wonderfully small, often compressed by 90%, or to only 1/10 of the size of the original data, which is very good when modems are involved. However, this fantastic compression efficiency comes with a high price. JPG uses lossy compression (lossy meaning "with losses"). Lossy means that some image quality is lost when the JPG data is compressed and saved, and this quality can never be recovered.

Most other file compression methods are lossless, which means "fully recoverable". Lossless compression always returns the original data, bit-for-bit identical without any question about differences (losses). We are used to saving data to a file, and getting it all back when we next open that file. Our Word and Excel documents, our Quicken data, any data at all, we cannot imagine NOT getting back exactly the original data. TIF, PNG, GIF, BMP and most other image file formats are lossless too. This integrity requirement does limit efficiency, limiting compression of photo image data to maybe only 10% to 40% reduction in practice (graphics can be smaller). But most compression methods have full lossless recoverability as the first requirement.

JPG files don't work that way. JPG is an exception. JPG compression is not lossless. JPG compression is lossy. Lossy means "with losses" to image quality. JPG compression has very high efficiency (relatively tiny files) because it is intentionally designed to be lossy, designed to give very small files without the requirement for full recoverability. JPG modifies the image pixel data (color values) to be more convenient for its compression method. Detail that doesn't compress well can be ignored (removed instead of retained). This allows amazing size reductions on the remainder, but when we open the file and expand the data to access it again, it is no longer the same data as before. This lost data is like lost purity or integrity. It can vary in degree, it can be fairly good, but it is always unrecoverable corruption of the data. This makes JPG be quite different from all the other usual file format choices.

There are times and places this compromise is an advantage. Web pages and email files need to be very small, to be fast through the modem, and some uses may not need maximum quality. In some cases, we are willing to compromise quality for size, sacrificing for the better good. And this is the purpose of JPG.

There is no magic answer providing both high compression and high quality. We don't get something for nothing, and the small size has a cost in quality. Still, mild quality losses may sometimes be acceptable for less critical purposes. The sample JPG images on next page show the kind of problem to expect from excessive compression.

Even worse, more quality is lost every time the JPG file is compressed and saved again, so ever editing a JPG image is a questionable decision. You should instead just discard the old JPG file and start over from your archived lossless TIF master, and save that change as the new JPG copy you need.

JPG compression can be adjusted to be better quality in a larger file, or to be lesser quality in a smaller file. When you save a JPG file, your FILE - SAVE AS dialog box should have an option for the degree of file compression. Some programs (Photoshop, PhotoImpact, PhotoDeluxe) call it JPG Quality. Other programs (Paint Shop Pro, Corel, Micrografx) call it JPG Compression. Same thing, but Quality runs numerically the opposite direction from Compression. High Quality corresponds to Low Compression. Typical values might be 80 Quality, or 20 Compression. These numbers are relative and have no absolute meaning. Compression in one program will vary from another even at the same number. The number is also not a percentage of anything, and Quality 100 does NOT mean no compression, it is just an arbitrary starting point. JPG will always compress, and Quality 90 is not so different from Quality 100 in practice. There's very little improvement over 95.

Individual image detail greatly affects compressibility. Large featureless areas (skies, walls, etc.) compress much better (smaller) than images containing much busy detail all over. Images with different content, all the same size in pixels and using the same JPG quality setting, may vary substantially in file size, half or perhaps even double the average size.
So the file size is only a very crude indicator of JPG quality, but for many images, file sizes smaller than 10% of the uncompressed image size often show excessive artifacts. A JPG file size only 10% of the bytes of that image's size in memory would be 10:1 compression, and this is the general ballpark for a fair tradeoff of quality vs. file size for color images of web page quality. Color compresses better than grayscale files, which must be larger, perhaps 20% of original size. These are very rough guidelines, your image, your photo program, your purpose, and your personal criteria or tolerance will all be different.

JPG is mathematically complex and requires considerable CPU processing power to decompress an image. JPG also allows several parameters, and programs don't all use the same JPG rules. Programs vary, some programs take shortcuts to load JPG faster but with less quality (browsers for example), and other programs load JPG slower with better quality. Final image quality can depend on the image details, on the degree of compression, on the method used by the compressing JPG program, and on the method used by the viewing JPG program.

I am sent many JPG images with questions why they appear "bad" and very "unclear", when the only problem is excessive JPG compression, too much, or saved too many times, or both. Too little Quality or too much Compression will affect JPG image quality visibly. It can be awful.
Learn to recognize JPG artifacts

You can and should learn to recognize this bad effect easily yourself. It's extremly important, but almost trivial to recognize, after you've seen it once. Scan a new image (you cannot salvage an old JPG image) and save it as a TIF file. Then, following that, also save the same image as a JPG file using a bit more than usual compression, a lower quality setting this time to help learn to see it. Then (very important) close that JPG image, and reopen that file to be sure you are viewing the contents of the file image you actually wrote (instead of the uncompressed image left on the screen that you thought you wrote).

Examine both images (TIF and JPG) on the same screen side by side, by zooming in to about 4 times size (400%, huge) on both. You will have to scroll around on them, but the 400% is to help you learn to recognize the artifacts this first time. The differences you see are the JPG artifacts of compression.

These JPG artifacts stand out clearly when compared to the uncompressed image. In general, the visible signs of excessive JPG compression are JPG artifacts, and which include:
· Areas of similar colors become blocky, like very large pixels. JPG compression merges similar colors into 8x8 pixel blocks of the same one color (this compresses well) and you see the 8x8 squares like big pixels. The enlargement also shows the actual small pixels which helps recognize the 8x8 block size.
· The sharp contrasting edges in the image will have vague dark smudges surrounding them. Excessive JPG compression is rough on all sharp edges in the image (especially so for text and graphic images). This is very counterproductive to apparent sharpness and fine detail.
· Some false color or color changes.
Here is a sample (135 KB) showing JPG artifacts in a photo image.
You can learn to recognize this easier the first time if you zoom in to about 400% size, and compare to a TIF file side-by-side. But the image can still be very usable at 100% size if the compression is mild. And now you know what to look for, and how to look for it, and how to judge if you want it.

Use a higher JPG Quality factor to minimize these effects (or better, don't use JPG at all if maximum quality is important). Less JPG Quality is more JPG compression, and worse artifacts. Normally you can always detect some artifacts even at high Quality factors.

JPG normally should not be used for text or graphic images. It blurs the sharp edges too much, and the results are typically poor. TIF, PNG, and GIF are vastly better for line art or graphic images, and these cases (solid colors instead of continuous tones) normally compress to a smaller file than JPG. JPG cannot contain line art or indexed color anyway. JPG requires 8 bit grayscale or 24 bit color. However for continuous tone photo images, as opposed to text or graphics, then files with high JPG Quality (low compression) are normally acceptable for viewing (read-only purposes), and the small file size is extremely desirable for modems.
But due to quality concerns, JPG compression is generally NOT suitable for archiving the important master copy of your image. With only mild compression, it might view OK, but you should grit your teeth, hold your breath, and cross your fingers for luck, if you ever have the need to modify and save a JPG file again. Because this will lower the quality of that image even more, every time you save the file. By "save", I mean to select the FILE - SAVE or FILE - SAVEAS menu with JPG format from an image program. That step does the JPG compression.

Note that opening and viewing JPG files is no problem at all. This does not save the file again, it does not alter the file in any way, and it does not create more artifacts. You can open and view a JPG file a jillion times without any concern (a web page for example). The artifacts are created only when the data is compressed for saving it as a JPG file. This happens only at the menus FILE - SAVE or FILE - SAVE AS when you select JPG format. Downloading or a simple file copy to another location also does not affect nor harm the JPG data in any way, as these steps involve no JPG compression step, they simply copy.

Archive your important master copy images in a non-lossy format (TIF, PNG, BMP), and then also make a JPG copy if needed for view-only purposes that need it to be smaller, like email and web pages.
You wont gain any quality by converting JPG to TIF now, because that image copy will still contain the JPG artifacts it had before. It is part of the image now, there is no way to improve it again. However, if you do need to edit a JPG, then saving it as TIF will prevent adding more artifacts by not doing another JPG Save, so TIF would be a good plan then.
If you find that you must edit the JPG image and must save it as JPG again, at least try to use the same program and same value of Quality or Compression every time you save the file. Using different values will use different parameters that will aggravate the damage due the lossy compression. I am certainly not suggesting repeated saving of JPG files with the same parameters is a good thing, but only that there are even worse ways to do it.

JPG format has a magic status for us, JPG is wonderful when the purpose is right, but we need to understand we pay a cost in quality. I know you surely will consider using JPG for master copies, everyone does at first, because the JPG file is so small, and the idea is frightfully appealing. But it's a high price paid in lost quality, and you will eventually come around to appreciate the quality of TIF files. I hope you will not have damaged important images that you cannot scan again. Some people argue that high quality JPG masters are not so bad. That's OK with me, it's your file, but the file size is one property of an image, and quality is another. You can choose either way. My goal is that you understand the effects of your choice in regard to your valuable master copies.

If you simply must use JPG for masters (if file size is the most important property of this image), then at least use the best Quality you can. Aim for a file size at least as large as 20% of memory size. For web images, size is indeed important, and a JPG file size 10% of uncompressed size is often a good tradeoff of quality for size for color images, but that is too extreme for any notion of a master copy. Grayscale images do not compress as much as color at the same settings, should be twice this percentage.

Then keep a master copy that you never rewrite. For any purpose, always start with a copy of that JPG master and never modify that JPG master itself. Saving that JPG master image again causes even more loss, permanent loss, so simply don't do it. If you simply need to flip it to vertical, or to scale it for printing, consider not saving that simple change at all, it is trivial to do again. But regardless, save any change to a different file, and never make your one master copy worse. You could of course just use a TIF master instead, and sleep better at night. And be aware that lowering scan resolution to reasonable values for the purpose is often the best size reduction you can make.

Judge your own common sense periodically. Why can't we see that a decent JPG image compressed to be only 20% of original size (still amazingly small, and still with artifacts), is more useful, and a much better deal, than one at 5% that is simply too awful to use? I know, the macho types are saying "but I can get it down to 2%". Then go for it man! <grin>

Note again that MOST other file formats (TIF, PNG, GIF, BMP) use lossless compression. These files are larger than JPG because they use milder, fully recoverable (lossless) compression to carefully preserve all of the original image data. It is a matter of data integrity instead of compression efficiency, and these other file formats remain full quality at all times, no matter how many times we might save them to a file. So we can save those as many times as we wish, and it always saves the full lossless quality. This is what we want for a master copy of the image.
The small JPG file size is great in its place, but it has a big price of reduced quality. There are proper times and places one would use it, and also major reasons one would not. There's nothing wrong with creating a JPG image using a moderate to high Quality factor to put a photo image on a web page or to send it via email. It's the only practical way. However there is an additional quality loss when we try to edit and save that JPG file a second time, so JPG is usually inappropriate for important archived master copies. The risk if you make this mistake now is that you cannot undo it in the future, so now is the best time to understand the situation.

A new JPEG 2000 file format is coming soon, available now but still rare. It uses wavelet compression, quite different but still lossy (said to be better quality). It is appearing now in some of the newest program versions, with various file extensions like .jp2, .jpx, .jpc, but web browsers will have to add support for it before it can become very popular. See the very worthwhile JPG FAQ by Tom Lane

Graphic Interchange Format (GIF)
======================

(.GIF file extension) There have been raging debates about the pronunciation. The designers of GIF say it is correctly pronounced to sound like Jiff. But that seems counter-intuitive, and up in my hills, we say it sounding like Gift (without the t).

GIF was developed by CompuServe to show images online (in 1987 for 8 bit video boards, before JPG and 24 bit color was in use). GIF uses indexed color, which is limited to a palette of only 256 colors (next page). GIF was a great match for the old 8 bit 256 color video boards, but is inappropriate for today's 24 bit photo images.

GIF files do NOT store the image's scaled resolution ppi number, so scaling is necessary every time one is printed. This is of no importance for screen or web images. GIF file format was designed for CompuServe screens, and screens don't use ppi for any purpose. Our printers didn't print images in 1987, so it was useless information, and CompuServe simply didn't bother to store the printing resolution in GIF files.

GIF is still an excellent format for graphics, and this is its purpose today, especially on the web. Graphic images (like logos or dialog boxes) use few colors. Being limited to 256 colors is not important for a 3 color logo. A 16 color GIF is a very small file, much smaller, and more clear than any JPG, and ideal for graphics on the web.

Graphics generally use solid colors instead of graduated shades, which limits their color count drastically, which is ideal for GIF's indexed color. GIF uses lossless LZW compression for relatively small file size, as compared to uncompressed data. GIF files offer optimum compression (smallest files) for solid color graphics, because objects of one exact color compress very efficiently in LZW. The LZW compression is lossless, but of course the conversion to only 256 colors may be a great loss. JPG is much better for 24 bit photographic images on the web. For those continuous tone images, the JPG file is also very much smaller (although lossy). But for graphics, GIF files will be smaller, and better quality, and (assuming no dithering) pure and clear without JPG artifacts.
If GIF is used for continuous tone photo images, the limited color can be poor, and the 256 color file is quite large as compared to JPG compression, even though it is 8 bit data instead of 24 bits. Photos might typically contain 100,000 different color values, so the image quality of photos is normally rather poor when limited to 256 colors. 24 bit JPG is a much better choice today. The GIF format may not even be offered as a save choice until you have reduced the image to 256 colors or less.
So for graphic art or screen captures or line art, GIF is the format of choice for graphic images on the web. Images like a company logo or screen shots of a dialog box should be reduced to 16 colors if possible and saved as a GIF for smallest size on the web. A complex graphics image that may look bad at 16 colors might look very good at say 48 colors (or it may require 256 colors if photo-like). But often 16 colors is fine for graphics, with the significance that the fewer number of colors, the smaller the file, which is extremely important for web pages.
GIF optionally offers transparent backgrounds, where one palette color is declared transparent, so that the background can show through it. The GIF File - Save As dialog box usually has an Option Button to specify which one GIF palette index color is to be transparent.
Interlacing is an option that quickly shows the entire image in low quality, and the quality sharpens as the file download completes. Good for web images, but it makes the file slightly larger.

GIF files use a palette of indexed colors, and if you thought 24 bit RGB color was kinda complicated, then you ain't seen nuthin' yet (next page).
For GIF files, a 24 bit RGB image requires conversion to indexed color. More specifically, this means conversion to 256 colors, or less. Indexed Color can only have 256 colors maximum. There are however selections of different ways to convert to 256 colors.

Davie

[Jean Jeanie]

Thanks. I'm now going for a quick lie down with a couple of paracetemol

Jean

[Dz]

Wow. Thanks, guys - but much contained in the above posts has been eclipsed by the realities of time, actual use/acceptance, and advancements in the art (and politics!) of image processing.
Some of it is just plain wrong.

ALL of the major image formats you are likely to encounter have some things in common: they are available in different qualities of color, grayscale, or 2-color black-and-white; they are available in different qualities of size compression; and most have readily-available free means of displaying them, editing them, and converting them between formats.

ALL of them stem from the need to include a "header" in the file which identifies the particular format used to save the image, whether or not a particular palette of colors/gray shades should be used, and certain parameters (image size, perhaps dots per inch - DPI, number of colors, etc.) necessary to recreate the photo as closely as possible. Some are in widespread use across many computer platforms, but some computer operating systems limit the types which are "natively" displayable, because of hardware design.

TIF - widely-used for PROFESSIONAL PRINTING (such as in the color photos used for large-format glossy calendars and magazines), extremely high-resolution color, large DPI and absolutely huge file sizes are the norm.

However, the TIF (Actually, TIFF - the "Tagged Image File Format") specification is flexible; intermediate levels of resolution can be used, and multiple forms of compression are available, so that file sizes begin to become manageable for a home computer. TIF Plug-ins for most internet browsers are readily available, if the browser doesn't natively display TIFs. If at all possible, NEVER use a website's special "file-viewer"; most come with network security problems you wouldn't want to invite, and none will warn you of the potential hazards. Instead, do a "direct" download of the file, saving it to your hard disk - or directly displaying it, then saving the image into a file (which need not be the TIF format!).

Since the mid- to late-1990s, the TIFF Group 4 ("G4") specification has been the international standard for fax transmissions of black-and-white pages. (The old "G3" spec is rarely used anymore.) The reason is simple: G4 Fax compression can boil down a 3 MB B/W image into a 50K-70K file size for transmission - and faithfully recreate every single dot in the original image when de-compressed. This G4 Fax format is precisely the one used for document images available from most government-operated websites: ScotlandsPeople, US Patent Office, and many, many other local-government sites.

TIF Hazards: Aside from the "extensible" nature of TIFF (which permits proprietary "extensions" which your program may not know how to handle), the only real hazard comes from high-end editing/display programs which offer "enhancement" of the saved images. DON'T BE TEMPTED to "enhance" the image - because all it will do is introduce "noise" that wasn't present in the original. (Such "enhancement" can make the image look prettier to your eyes, by adding subtle gray-shading to text or handwriting. But doing so can easily quadruple the size of the file, making it impossible to be converted back to the small 2-color original format without making it unreadable.) Some clearly black-and-white images here in the TS gallery have been "enhanced" in this way - and can no longer be "down-converted" and remain readable.

BMP - a truly bizarre creation of Microsoft, which intentionally does everything backwards from every other image file type. Nearly useless as a storage format (files are much too big, and take up oodles of memory), most microsoft-written programs internally convert all other available formats to BMP before use by windows. No browser bothers to display this exclusionary format natively - and I don't think anyone has written a plug-in for this true "orphan" format.
Convert BMP images to something else at your first opportunity; you'll save plenty of hard-disk space. BMP was *NEVER* a "basic picture format".

PCX - the first format to support up to 24-bit color imaging with moderate compression always built in, it faithfully reproduced every pixel in the original image. No browser displays PCXs natively, even though the format was quickly published in the public domain. An Intel-only (no Macs) product, it is still a very useful, compact format, though showing its age.

GIF - Compuserve's proprietary format for compressed 256-color, 64-color grayscale, and b/w images used the proprietary LZW compression format, and demanded royalties from software developers using the GIF standards. (There are two: GIF87, and GIF89. The latter offers the choice of a "transparent" color - very useful to permit the background on a webpage to show through.) For a lot of years, GIF images were considered THE standard for bulletin boards and early internet websites. However, the demand for LZW royalties knocked GIF from that throne - and led to creation of the PNG format and more widespread use of JPGs. Compressed GIFs are "lossless"; nothing is lost during compression. Imaging "snobs" may turn up their nose to GIF's 256-color images as "lacking color definition" but most people can't see a visual difference between a GIF and a JPG or TIF.

JPG - (Or more correctly, JPEG, with JFIF, the most-common variety) is today the most common form of image on the internet. With compression quality figures of 70% - 85%, losses of image quality simply aren't visible to the eye. Quality figures over 85% usually just make the new file larger than the original, without noticeably increasing image quality. Excellent-quality JPGs can be made with as few as 2-colors (b/w) - but your browser may not be capable of saving it as anything other than the larger (standard) 24-bit color.

PNG - So much promise, so little use. Most browsers can readily display PNG images (and those that don't can obtain plug-ins for the purpose... with the possible exception of Internet Exploder). The bright future promised so long ago for PNGs never really materialized. It is an excellent format, capable of everything any of the others can do (including very highly-compressed b/w images just 1-2% larger than TIF's Group 4 Fax format) - but seriously under-used.

I compiled a nice TIF2PNG executable program (which could readily eliminate those dangerous website TIF "viewers", if your browser displays PNGs) - but it would require websites (such as ScotlandsPeople) to run the conversion immediately prior to sending the image to you. Anyone desiring a copy can email me at f4wcs@yahoo.com - as long as it is NOT used commercially. It can make your Grp 4 TIFs shareable with others who do not possess a TIF reader.

.

[mesklin]

Please note that the first post was headed 'Computer Novice'

Jean's second post mentioned 'Paracetamol'

So much detail, and so, so little reading of post.

I believe that a simple explanation was called for.

Yes, you can kill ants with an anvil, but there are simpler ways.

Dave

[ellenavon]

Oh my giddy aunt! Jean I'm with you on this one!

Ellen.

[Jean Jeanie]

More paracetamol please. I feel another lie down coming on

Jean

[Laura]

Jean and Ellen,

Average ability twelve year olds are expected to learn this stuff if they wish to take computer classes in our local schools.

Good Luck,
Laura

[ellenavon]

Yes, but I'm not 12!!!

However, I am determined - and these minor (!) gaps in my knowledge (either the genealogy or the computer "stuff") will not beat me - I will learn.

Ellen.