Photo Image file formats, TIF, JPG, PNG, GIF. Which to use?
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Image File Formats - JPG, TIF, PNG, GIF
Which to use?
The most common image file formats, the most important for cameras,
printing, scanning, and internet use, are JPG, TIF, PNG, and GIF.
JPG is the most used image file format. JPG is the file extension for
JPEG files (Joint Photographic Experts Group, committee of ISO and
ITU). Digital cameras and web pages normally use JPG files - because
JPG heroically compresses the data to be very much smaller in the
file. However JPG uses lossy compression to accomplish this feat, which
is a strong downside. A smaller file, yes, there is nothing like JPG for
small, but this is at the cost of image quality. This degree is selectable
(with an option setting named JPG Quality), to be lower quality smaller
files, or to be higher quality larger files. In general today, JPG is rather
unique in this regard, using lossy compression allowing very small files
of lower quality, whereas almost any other file type uses lossless
compression (and is larger). The meaning of Lossy is discussed Below.
Frankly, JPG is used when small file size is more important than
maximum image quality (web pages, email, memory cards, etc). But
JPG is good enough in many cases, if we don't overdo the compression.
Perhaps good enough for some uses even if we do overdo it (web
pages, etc). But if you are concerned with maximum quality for
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archiving your important images, then you do need to know two things: 1) JPG should always
choose higher Quality and a larger file, and 2) do NOT keep editing and saving your JPG images
repeatedly, because more quality is lost every time you save it as JPG (in the form of added JPG
artifacts... pixels become colors they ought not to be - lossy). More at the JPG link at page
bottom.
TIF is lossless (including LZW compression option), which is considered the highest quality format
for commercial work. The TIF format is not necessarily any "higher quality" per se (the same RGB
image pixels, they are what they are), and most formats other than JPG are lossless too. TIF
simply has no JPG artifacts, no additional losses or JPG artifacts to degrade and detract from the
original. And TIF is the most versatile, except that web pages don't show TIF files. For other
purposes however, TIF does most of anything you might want, from 1-bit to 48-bit color, RGB,
CMYK, LAB, or Indexed color. Most any of the "special" file types (for example, camera RAW files,
fax files, or multipage documents) are based on TIF format, but with unique proprietary data tags
- making these incompatible unless expected by their special software.
GIF was designed by CompuServe in the early days of computer 8-bit video, before JPG, for video
display at dial up modem speeds. GIF discards all Exif data, and because GIF was designed for
video screen purposes, GIF does Not retain printing resolution values. GIF always uses lossless
LZW compression, but it is always an indexed color file (1 to 8-bits per pixel). GIF can have a
palette of 24-bit colors, but only 256 of them maximum (which colors depend on your image
colors). GIF is rather limited colors for color photos, but is generally great for graphics. Repeating,
don't use indexed color for color photos today, the color is too limited. GIF offers transparency
and animation. PNG and TIF files can also optionally handle the same indexed color mode that GIF
uses, but they are more versatile with other choices too (can be RGB or 16 bits, etc). But GIF is
still very good for web graphics (i.e., with a limited number of colors). For graphics of only a few
colors, GIF can be much smaller than JPG, with more clear pure colors than JPG). Indexed Color is
described at Color Palettes (second page of GIF link below).
PNG can replace GIF today (web browsers show both), and PNG also offers many options of TIF
too (indexed or RGB, 1 to 48-bits, etc). PNG was invented more recently than the others,
designed to bypass possible LZW compression patent issues with GIF (which never actually
became any issue). And since PNG was more modern, it offers other options too (RGB color
modes, 16 bits, etc). One additional feature of PNG is transparency for 24 bit RGB images.
Normally PNG files are a little smaller than LZW compression in TIF or GIF (all of these use
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lossless compression, of different types), but PNG is a bit slower to read or write. That patent
situation has gone away now, but PNG remains excellent lossless compression. Less used than TIF
or JPG, but PNG is another good choice for lossless quality work.
Camera RAW files are very important of course, but RAW files must be processed to regular
formats (JPG, TIF, etc) to be viewable and usable in any way. However, the point is that RAW
offers substantial benefit in doing that, one of which is we can choose our settings AFTER we can
see the image, and what it needs, and what helps it. The debate goes on, some cannot imagine
NOT taking advantage of the greater opportunities of RAW. Others think any extra step is too
much trouble, and are satisfied with JPG - my own biased opinion is they just don't know yet. :)
More detail Below.
We could argue that there really is no concept of RAW files from the scanner (scanners are RGB).
Vuescan does offer an output called RAW, which is 16 bit, but RGB, not raw. The difference is that
it defers gamma correction until a later pass. And it can include the scanners fourth Infrared noise
correction channel data if any. Vuescan itself is the only post-processor for these. But scanner
color images are already RGB color, instead of Bayer pattern raw data like from cameras.
Camera RAW images are not RGB, and must be converted to RGB for any use (our monitors and
printers expect RGB images). The idea and big advantage of camera raw is that all camera and
JPG processing options (such as white balance and contrast) are deferred until later, when we can
see the image to decide what it precisely needs without having to undo JPG processing. That
makes it better, and much easier to get it right. Then the converted RGB image can be saved only
one time as high quality JPG (no JPG artifact issues). When and if the image needs additional
processing, we discard that JPG copy and resume from the raw archive original.
I recommend always archiving your original unedited image from camera or scanner. Keep it forever,
whatever format it is, JPG, Raw, whatever. Your download folder should be your permanent archive
location of the unchanged original file. Then when editing that image, always save any change to a
different location, always. Never overwrite or delete your only original file. Always keep your pristine
original. There will be times you need some of them, especially the one really important one. If you
did update that original file a few times, for white balance, brightness, resampling or cropping,
quality suffers, and it is irreversible and the original image is lost. Don't destroy your original
image. Work on a copy. Beginners tend to worry about the disk space used by that archive, but this
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is just the nature of the game, JPGs are small anyway, and disks are
inexpensive (4 TB Western Digital USB 3.0 external, about $100
USD). Disk space becomes a trivial concern. Retaining your original
image is not trivial. Make a frequent backup too, on another disk. It's
a choice of being safe now, or sorry later.
Different color modes have different size data values, as shown.
Image Type
1 bit Line art
8 bit Indexed
Color
Bytes per pixel
1/
Possible colors
File
Types
(1 bit per pixel)
2 colors,
black or white
TIF,
PNG
Up to 1 byte per
pixel
256 colors maximum.
Graphics use today
TIF,
PNG,
GIF
8 byte per pixel
8 bit
Grayscale
1 byte per pixel
256 shades of gray
JPG,
TIF,
PNG
16 bit
Grayscale
2 bytes per pixel
65636 shades of gray
TIF,
PNG
24 bit RGB
3 bytes per pixel
(one byte for
each of R, G, B)
16.77 million colors.
The "Norm" for photos,
e.g., JPG
JPG,
TIF,
PNG
32 bit CMYK
4 bytes per pixel,
for Prepress
Varies, but low. One
guess has been approx
160,000 colors
TIF
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48 bit RGB
6 bytes per pixel
File Type Property
TIF,
PNG
2.81 trillion colors
TIF
PNG
GIF
Lossless compression
X
X
X
Uncompressed option
X
X
Lossy compression
JPG
X
Grayscale
X
X
X
RGB color
X
X
X
8 bit color (24 bit data)
X
X
X
16 bit color option
X
X
CMYK or LAB color
X
Indexed color option
X
Transparency option
Animation option
X
X
X
X
X
Image Type and Data Size Calculator
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Image Size:
x
pixels
Data Type:
If Printed at:
pixels per inch
Compute
Image Size
6000x4000 pixels, 24,000,000 pixels,
24 Megapixels, Aspect Ratio 3:2 (1.5:1)
Data Size
72,000,000 Bytes, 68.665 MB, 3 bytes per pixel
File Size
Varies with degree of data compression. These
are simple approximations, but perhaps roughly
TIF file uncompressed: 72.098 MB
TIF LZW: 41.199 MB (lossless)
PNG:
36.392 MB (lossless)
JPG of 1/4 size: 17.166 MB (fine)
JPG of 1/8 size: 8.583 MB (normal)
JPG of 1/16 size: 4.292 MB (basic)
Print Size
24 x 16 inches if printed at 250 pixels per inch
(61 x 40.6 centimeters)
Note that 24-bit RGB data (like JPG) is three bytes per pixel, regardless of image size. See more
detail.
Best file types for these general purposes:
Photographic Images
Graphics, including Logos or Line art
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Properties
Photos are continuous
tones, 24-bit color or 8-bit
Gray
Graphics are often solid colors, with few
colors, limited to 256 colors, with text or
lines and sharp edges
For Unquestionable
Best Image Quality
TIF LZW or PNG (lossless
compression,
and no JPG artifacts)
PNG or TIF LZW (lossless compression,
without JPG artifacts)
Smallest File Size
JPG with a higher Quality
factor can be both small
decent quality.
TIF LZW or GIF or PNG (graphics/logos
without gradients normally permit indexed
color of 2 to 16 colors for smallest file
size)
Maximum
Compatibility:
Windows, Mac, Unix
TIF or JPG
TIF or GIF
Worst Choice
256 color GIF is very limited
color, and is a larger file
than 24 -bit JPG
JPG compression adds artifacts, smears
text and lines and edges
These are not the only choices, but they are good and reasonable choices.
More information:
PNG Format
TIF Format
JPG Format
GIF Format
Major considerations to choose the necessary file type include:
Compression quality - Lossy type for smallest files (JPG), or Lossless type for best quality images
(TIF, PNG). Compression varies with type of compression, but degree of compression also varies
with the image content (bland areas with sparse detail, like walls or sky, compress very
effectively, But high detail areas compress less effectively).
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Full RGB color is for photos (TIF, PNG, JPG),
or Indexed Color is for graphics (PNG, GIF, TIF).
16-bit color (48-bit RGB data) is sometimes desired (TIF and PNG). Wide-range tonal shifts
(gamma and white balance) in the initial editing processing can benefit from more than 8-bits.
Scanners and cameras are at least 12-bits for this reason.
However our monitors and printers expect 8-bit data. And JPG is only 8-bits.
Type PNG-24 is 24-bit RGB color for photos, PNG-8 is Indexed color for graphics.
GIF is indexed color only, but indexed is an option in TIF and PNG.
Transparency or Animation is used in graphics (GIF and PNG).
Documents - graphics and text - line art, multi-page, fax, etc - this will be TIF, typically with LZW
compression.
Commercial prepress wants CMYK color (TIF files).
See Properties chart above. We select the file type that supports the properties we need.
The only reason for using lossy compression is for smaller file size, usually for internet transmission
speed or storage space. Web pages require JPG or GIF or PNG image types, because some browsers
do not show TIF files. On the web, JPG is the clear choice for photo images (smallest file, with image
quality being less important than file size), and GIF is common for graphic images, but indexed color
is not normally used for color photos (PNG can do either on the web).
Other than the web, TIF file format has been the undisputed leader when best quality is desired,
largely because TIF is so important in commercial printing environments. High Quality JPG can be
pretty good too, but don't ruin them by making the files too small. If the goal is high quality, you
don't want small. Only consider making JPG large instead, and plan your work so you can only save
them as JPG only one or two times. Adobe RGB color space may be OK for your home printer and
profiles, but if you send your pictures out to be printed, the mass market printing labs normally only
accept JPG files, and only process sRGB color space.
What does JPG Quality Losses mean?
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What are JPG artifacts?
Something we all need to know, but it takes more to show this, so it
was placed on its own page.
Difference in photo and graphics images
Photo images have continuous tones, meaning that adjacent pixels
often have very similar colors, for example, a blue sky might have
many shades of blue in it. Normally this is 24-bit RGB color, or 8-bit
grayscale, and a typical color photo may contain perhaps a hundred
thousand RGB colors, out of the possible set of 16 million colors in 24bit RGB color.
Graphic images are normally not continuous tone (gradients are possible in graphics, but are seen
less often). Graphics are drawings, not photos, and they use relatively few colors, maybe only two or
three, often less than 16 colors in the entire image. In a color graphic cartoon, the entire sky will be
only one shade of blue where a photo might have dozens of shades. A map for example is graphics,
maybe 4 or 5 map colors plus 2 or 3 colors of text, plus blue water and white paper, often less than
16 colors overall. These few colors are well suited for Indexed Color, which can re-purify the colors.
Don't cut your color count too short though - there will be more colors than you count. Every edge
between two solid colors likely has maybe six shades of anti-aliasing smoothing the jaggies (examine
it at maybe 500% size). Insufficient colors can rough up the edges. Scanners have three modes to
create the image: color (for all color work), grayscale (like B&W photos), and lineart. Line art is a
special case, only two colors (black or white, with no gray), for example clip art, fax, and of course
text. Low resolution line art (like cartoons on the web) is often better as grayscale, to add antialiasing to hide the jaggies.
JPG files are very small files for continuous tone photo images, but JPG is poor for graphics, without
a high Quality setting. JPG requires 24-bit color or 8-bit grayscale, and the JPG artifacts are most
noticeable in the hard edges of graphics or text. GIF files (and other indexed color files) are good for
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graphics, but are poor for photos (too few colors possible). However, graphics are normally not many
colors anyway. Formats like TIF and PNG can be used either way, 24-bit or indexed color - these file
types have different internal modes to accommodate either type optimally.
Basics
Our digital images are dimensioned in pixels (not bytes, and definitely not inches). And a pixel is
simply a color definition, the color that this tiny dot of image sampled area ought to be. Put all those
colored dots together, and our brain sees the image. The losses of image data we are speaking
about is about the altered color of the pixels.
Image data consists of pixels, and pixels are "colors", simply the storage of the three RGB data
components (see What is a Digital Image Anyway?).
Any 24-bit RGB image will use three bytes per pixel (see Color Bit-Depth - Memory Size).
So - for example- any 10 megapixel camera image data will occupy 3x10 = 30 million bytes, by
definition of RGB color. This number is the "data size" (when opened into computer memory for use).
A TIF file will be near that size (and is lossless), but JPG is normally compressed very heavily (lossy,
not lossless) to store in a JPG file of perhaps 1/10 this size (variable with JPG Quality setting), which
is "file size" (not image size and not data size). This example image size is still 10 megapixels
(dimensioned in pixels, width x height), and the data size is 30 million bytes, but the JPG file size
might be 3 MB (lossy compression takes a few liberties). The image will still come out of the JPG file
as the same 10 megapixels and the same 30 million bytes when the 3 MB JPG file is opened. We
hope its quality also comes out about the same - the JPG losses are altered color values of some of
the pixels).
Image size (pixels) determines how we can use the image - everything is about the pixels. See a
summary of digital basics.
All photo editor programs will support these file formats, which will generally support and store
images in the following color modes:
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Color data mode of File Types, bits per pixel
JPG
RGB - 24-bits (8-bit color), or Grayscale - 8-bits
Always uses lossy JPG compression, but its degree is selectable, for higher quality and larger
files, or lower quality and smaller files. JPG is for photo images, and is the worst choice for most
graphics or text data.
TIF
Versatile, many formats supported.
Mode: RGB or CMYK or LAB, and others, almost anything.
8 or 16-bits per color channel, called 8 or 16-bit "color" (24 or 48-bit RGB files).
Grayscale - 8 or 16-bits,
Indexed color - 1 to 8-bits,
Line Art (bilevel)- 1-bit
For TIF files, most programs allow either no compression or LZW compression (LZW is lossless,
but is less effective for color images). Adobe Photoshop also provides JPG or ZIP compression in
TIF files too (but which greatly reduces third party compatibility of TIF files). "Document
programs" allow ITCC G3 or G4 compression for 1-bit text (Fax is G3 or G4 TIF files), which is
lossless and tremendously effective (small). Many specialized image file types (like camera RAW
files) are TIF file format, but using special proprietary data tags.
24-bits is called 8-bit color, three 8-bit bytes for RGB (256x256x256 = 16.7 million colors
maximum.)
Or 48-bits is called 16-bit color, three 16-bit words (65536x65536x65536 = trillions of colors
conceptually)
PNG
RGB - 24 or 48-bits (called 8-bit or 16-bit "color"),
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Alpha channel for RGB transparency - 32 bits
Grayscale - 8 or 16-bits,
Indexed color - 1 to 8-bits,
Line Art (bilevel) - 1-bit
Supports transparency in regular indexed color, and also there can be a fourth channel (called
Alpha) which can map RGB graduated transparency (by pixel location, instead of only one color,
and graduated, instead of only on or off).
The APNG version also supports animation (like GIF), showing several sequential frames fast to
simulate motion.
PNG uses ZIP compression which is lossless, and somewhat more effective color compression
than GIF or TIF LZW. For photo data, PNG is somewhat smaller files than TIF LZW, but larger
files than JPG (however PNG is lossless, and JPG is not.) PNG is a newer format than the others,
designed to be both versatile and royalty free, back when the patent for LZW compression was
disputed for GIF and TIF files.
GIF
Indexed color - 1 to 8-bits (8-bit indexes, limiting to only 256 colors maximum.) Color is 24-bit
color, but only 256 colors.
One color in indexed color can be marked transparent, allowing underlaying background to be
seen (very important for text, for example). GIF is an online video image, the file contains no dpi
information for printing. Designed by CompuServe for online images in the days of dialup and
8-bit indexed computer video, whereas other file formats can be 24-bits now. However, GIF is
still great for web use of graphics containing only a few colors, when it is a small lossless file,
much smaller and better than JPG for this. GIF files do not save the dpi number for printing
resolution.
GIF uses lossless LZW compression. (for Indexed Color, see second page at GIF link at page
bottom).
GIF also supports animation, showing several sequential frames fast to simulate motion.
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Note that if your image size is say 3000x2000 pixels, then this is 3000x2000 = 6 million pixels (6
megapixels). Assuming this 6 megapixel image data is RGB color and 24-bits (or 3 bytes per pixel of
RGB color information), then the size of this image data is 6 million x 3 bytes RGB = 18 million
bytes. That is simply how large your image data is (see more). Then file compression like JPG or
LZW can make the file smaller, but when you open the image in computer memory for use, the JPG
may not still have the same image quality, but it is always still 3000x2000 pixels and 18 million
bytes. This is simply how large your 6 megapixel RGB image data is (megapixels x 3 bytes per
pixel).
Summary
The most common image file formats, the most important for general purposes today, are JPG, TIF,
PNG and GIF. These are not the only choices of course, but they are good and reasonable choices for
general purposes. Newer formats like JPG2000 never acquired popular usage, and are not supported
by web browsers, and so are not the most compatible choice.
PNG and TIF LZW are lossless compression, so their file size reduction is not as extreme as the wild
heroics JPG can dream up. In general, selecting lower JPG Quality gives a smaller worse file, higher
JPG Quality gives a larger better file. Your 12 megapixel RGB image data is three bytes per pixel, or
36 million bytes. That is simply how big your image data is. Your JPG file size might only be only
5-20% of that, literally. TIF LZW might be 65-80%, and PNG might be 50-65% (very rough ballpark
for 24-bit color images). We cannot predict sizes precisely because compression always varies with
image detail. Blank areas, like sky and walls, compress much smaller than extremely detailed areas
like a tree full of leaves. But the JPG file can be much smaller, because JPG is not required to recover
the original image intact, losses are acceptable. Whereas, the only goal of PNG and TIF LZW is to be
100% lossless, which means the file is not as heroically small, but there is never any concern about
compression quality with PNG or TIF LZW. They still do impressive amounts of file size compression,
remember, the RGB image data is actually three bytes per pixel.
Camera RAW files is one way to bypass this JPG issue, at least until the last one final save as JPG
when required. And it offers additional processing advantages too. Better easier tools in RAW than
JPG has, the RAW data has wider range than JPG has. Much the same controls as in the camera,
which you would have needed anyway, but this step is done after you see the camera results, to
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know exactly what it still needs, and can simply tweak and judge it by eye (as opposed to settings in
the camera done in advance, as hopeful wishing).
We hear: But RAW images require an editing step first. Some people do seem terrified of the
word "edit", but no matter what, we do always have to stop and look at our images on the computer,
every one of them. That is the same extra step. Surely we have to crop them a bit, and resample
smaller, and many of mine will need a slight Exposure or White Balance tweak to be their best. It
makes a tremendous difference. That is the same editing, a few seconds each, a few clicks, and then
the file must be saved again. You might as well do this step in the RAW software, which has better
easier tools to do it, and more range to do it., and of course, we can SEE the image now. If your
session included 100 images of same lighting situation, just select them all, edit ONE of them (say
White Balance and Exposure, even Cropping, etc), and the same edit clicks are applied to all of the
selected RAW images in one click. Extremely convenient. And no JPG artifacts of course, no losses,
and any changes can easily be Undone anytime later, with full recovery of our original RAW master
copy. RAW is the trivial, easy, and good way, Day and Night good, if you care about these things.
We all have our own notions, but here is a popular opinion about the ultimate, in quality, in
versatility, in convenience. RAW files are popular indeed, from most DSLR cameras. When we take
any digital picture, the camera has a RAW sensor, but normally processes and outputs the image as
a JPG file. But often we can choose to output the original RAW image instead, to defer that JPG step
until later. We cannot view or use that RAW file any way other than to process it in computer
software and then output a final TIF or JPG image, however postponing this processing offers a few
serious advantages, better editing options, and we can bypass all JPG artifacts entirely, until the one
final output Save for whatever purpose. RAW allows us to tweak exposure and color, and defer White
Balance decisions until later when we can see the image first, and judge any trial results. The 12-bit
RAW file offers greater range for any of our adjustments, often on multiple files simultaneously. And
RAW always preserves the intact original version, so we can easily back out any editing changes we
made, crop size for example. An argument is made that processing RAW requires this extra step, but
of course, same is true of any editing that is required. RAW is the easy way, with the best results.
The Next button will browse through the descriptions on the next pages, or you can use these
shortcut links directly:
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