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I would like to know which one of these formats requires less memory for the same quality of the picture, and what the main differences between the formats are.

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Btw, JPG and JPEG both refer to the same thing (see e.g. en.wikipedia.org/wiki/JPEG) so the title could be simplified a little. –  Jonik Oct 10 '09 at 10:22
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Not sure how my answer doesn't answer your original question, and how your chosen answer does...? :-/ –  Django Reinhardt Dec 11 '11 at 21:26
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> which one of these formats requires less memory Um, define “less memory”. Do you mean it takes up less disk space? (JPEG for photos, PNG and/or GIF for screenshots.) Do you mean the compressed file takes less space in memory? (Same as disk space.) Do you mean the decoded image takes less space in memory (None; they are all essentially the same when decoded to raw.) –  Synetech Feb 17 '12 at 3:52
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8 Answers 8

up vote 37 down vote accepted

From What is the difference between TIFF, GIF, JPG, JPEG, PNG, and a BMP file?

BMP - Bitmap. This was probably the first type of digital image format that I can remember. Every picture on a computer seemed those days to be a BMP. In Windows XP the Paint program saves its images automatically in BMP. However, in Windows Vista and later images are now saved to JPEG. BMP is the basis platform for many other file types.

JPG / JPEG - (Joint Photographic Experts Group) Jpeg format is used for color photographs, or any pictures with many blends or gradients. It is not good with sharp edges and tends to blur them a bit unless stored at high quality. This format became popular with the invention of the digital camera. Most, if not all, digital cameras download photos to your computer as a Jpeg file. Obviously the digital camera manufacturers see the value in high quality images that ultimately take up less space.

GIF - (Graphics Interchange Format) Gif format is best used for text, line drawings, screenshots, cartoons, and animations. Gif is limited to a total number of 256 colors or less, so Gif images are relatively small. It is commonly used for fast loading web pages. It also makes a great banner or logo for your web-page. Animated pictures can also be saved in GIF format as a sequence of static images. For example, a flashing banner would be saved as a Gif file.

PNG - (Portable Networks Graphic) Apparently this is one of the best image formats, however it was not always compatible with all web browsers or image software. Nowadays it is the best image format to use for website. I use .png for logos and screenshots.

TIFF - (Tagged Image File Format) This file format has not been updated since 1992 and is now owned by Adobe. It can store an image and data (tag) in the one file. TIFF can be compressed, but it is rather its ability to store image data in a lossless format that makes a TIFF file a useful image archive, because unlike standard JPEG files, a TIFF file using lossless compression (or none) may be edited and re-saved without losing image quality. This file is commonly used for scanning, faxing, word processing, and so on. It is no longer a common file format to use with your digital photos, as jpeg is great quality and takes up less space.

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Be aware that without a "hack" of sorts, IE6 still does not support alpha transparency in PNG files i.e. areas of transparency that are semi opaque –  Josh Comley Oct 15 '09 at 11:53
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...and a surprising amount of people still use IE6 (tinyurl.com/56kp). And MS want to support it until 2014! :( (tinyurl.com/qvdyn5) –  Josh Comley Oct 15 '09 at 12:05
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BMP: This is not the basis for other file formats. As far as I know the BMP header and file structure are not shared with other formats (contrary to TIFF, for example). JPEG: It was created and existed on the web way before digital cameras became prevalent. Also many digital cameras allow for saving a "raw" format which usually is a TIFF, albeit with vendor-specific contents. GIF: Not restricted to 256 colors per image, only to 256 colors per frame (see en.wikipedia.org/wiki/Graphics_Interchange_Format#True_color). –  Joey Oct 18 '09 at 20:57
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TIFF: The prevalent file and container format for raw images from digital cameras (the non-point-and-shoot ones). TIFF allows for nearly arbitrary data (hence tagged) in it which also means that it supports arbitrary compression methods from LZW (GIF), LZ77 (PNG) to JPEG and others. Also TIFF allows for multiple images (pages) in one file. –  Joey Oct 18 '09 at 21:01
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While the answer is good at answering the difference of the picture formats in terms of history and general usage, the original answer asked about relative sizes and quality too... –  camster342 Jun 13 '11 at 11:26
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In xkcd style from lbrandy.com:

alt text

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Illustrates the point nicely :) (even if I've never seen anyone advocate such 'Always JPEG!' policy) –  Jonik Oct 15 '09 at 11:47
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+1 Since this picture illustrates the jpeg problem so well... –  Johan Oct 15 '09 at 11:53
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I wish I could double upvote! I send this to everybody who sends me crappy jpegs! –  Tim Büthe Oct 15 '09 at 12:00
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@Teddy - you were absolutely right. I misread when I copied it, it said xkcd style, not from xkcd. I have fixed the text and link. –  Robert MacLean Oct 15 '09 at 12:17
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© 2008 Louis Brandy. All Rights Reserved....? –  Arjan Oct 15 '09 at 12:29
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You should be aware of a few key factors...

First, there are two types of compression: Lossless and Lossy.

Lossless means that the image is made smaller, but at no detriment to the quality. Lossy means the image is made (even) smaller, but at a detriment to the quality. If you saved an image in a Lossy format over and over, the image quality would get progressively worse and worse.

There are also different colour depths (palettes): Indexed color and Direct color.

With Indexed it means that the image can only store a limited number of colours (usually 256) that are chosen by the image author, with Direct it means that you can store many thousands of colours that have not been chosen by the author.


BMP - Lossless / Indexed and Direct

This is an old format. It is Lossless (no image data is lost on save) but there's also little to no compression at all, meaning saving as BMP results in VERY large file sizes. It can have palettes of both Indexed and Direct, but that's a small consolation. The file sizes are so unnecessarily large that nobody ever really uses this format.

Good for: Nothing really. There isn't anything BMP excels at, or isn't done better by other formats.

BMP vs GIF


GIF - Lossless / Indexed only

GIF uses lossless compression, meaning that you can save the image over and over and never lose any data. The file sizes are much smaller than BMP, because good compression is actually used, but it can only store an Indexed palette. This means that there can only be a maximum of 256 different colours in the file. That sounds like quite a small amount, and it is.

GIF images can also be animated and have transparency.

Good for: Logos, line drawings, and other simple images that need to be small. Only really used for websites.

GIF vs JPEG


JPEG - Lossy / Direct

JPEGs images were designed to make detailed photographic images as small as possible by removing information that the human eye won't notice. As a result it's a Lossy format, and saving the same file over and over will result in more data being lost over time. It has a palette of thousands of colours and so is great for photographs, but the lossy compression means it's bad for logos and line drawings: Not only will they look fuzzy, but such images will also have a larger file-size compared to GIFs!

Good for: Photographs. Also, gradients.

JPEG vs GIF


PNG-8 - Lossless / Indexed

PNG is a newer format, and is really a good replacement for GIFs. Sadly, however, it has a few drawbacks: Firstly it cannot support animation like GIF can (well it can, but only Firefox seems to support it, unlike GIF animation which is supported by every browser). Secondly it has some support issues with older browsers like IE6. Thirdly, important software like Photoshop have very poor implementation of the format. (Damn you, Adobe!) It can only save images of 256 colours, like GIFs.

Good for: One wonderful thing that PNG-8 does better than GIFs is having support for Alpha Transparency.

PNG-8 vs GIF

Important Note: Photoshop does not support Alpha Transparency for PNG-8 files. (Damn you, Photoshop!) There are ways to convert Photoshop PNG-24 to PNG-8 files while retaining their transparency, though. One method is PNGQuant, another is to save your files with Fireworks.


PNG-24 - Lossless / Direct

PNG-24 is a great format that combines Lossless encoding with Direct color (thousands of colours, just like JPEG). It's very much like BMP in that regard, except that PNG actually compresses images, so it results in much smaller files. Unfortunately PNG-24 files will still be much bigger than JPEGs, GIFs and PNG-8s, so you still need to consider if you really want to use one.

Even though PNG-24s allow thousands of colours while having compression, they are not intended to replace JPEG images. A photograph saved as a PNG-24 will likely be at least 5 times larger than a equivalent JPEG image, which very little improvement in visible quality. (Of course, this may be a desirable outcome if you're not concerned about filesize, and want to get the best quality image you can.)

Just like PNG-8, PNG-24 supports alpha-transparency, too.

I hope that helps!

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Good illustration. Watch out for artifacts caused by compression. I think JPEG like video compression formats has the problem where solid red zones will tend to "bleed" on the edges. –  James Poulson Jun 13 '11 at 12:16
    
Note that in the last page, you could've gotten at-least-equal quality at the same-or-lower filesize with PNG-8 instead of PNG-24 –  dtech Sep 26 '11 at 18:56
    
That's true. Plus there's PNG-8 with Alpha Transparency, but I suppose I was trying to show its ultimate strengths. Maybe I'll expand on it. –  Django Reinhardt Sep 28 '11 at 23:29
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You're wrong about PNG not supporting animation. PNG can do it fine, most viewers and browsers don't support it. en.wikipedia.org/wiki/APNG Firefox supports it pretty well, it seems. people.mozilla.com/~dolske/apng/demo.html –  Rob Jan 17 '12 at 17:19
    
Wow. I never knew that. Thanks for pointing it out! I guess with no Photoshop support (they really don't like PNG do they?) and no Internet Explorer/Safari/Chrome support, it's pretty useless for most purposes. Thanks for sharing, though. –  Django Reinhardt Jan 17 '12 at 23:50
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The existing answers include very little technical data, so I'll include that here.

  • JPEG: up to 24-bit color (possibly more?), variable (usually high) compression, lossy, no alpha support
  • PNG: up to 48-bit color, moderate compression, lossless, alpha support
  • BMP: up to 24-bit color, very little compression, lossless, alpha support
  • GIF: up to 8-bit color, little compression, lossless, transparency support, animation support

Color Depth

  • 8-bit color == 256 colors
  • 24-bit color == 16,777,216 colors
  • 48-bit color == 281,474,976,710,656 colors

Most computer monitors run at 24-bit color depth. The human eye can distinguish about that many colors. Additional color depth is mostly to be able to retain information from a sensor so that manipulation of a photograph has more data to work with. Trying to represent a photograph in 8-bit color is going to result in graininess.

Compression

This basically refers to how large the final file will be. More compression equals a smaller file. However, JPEG attains small file sizes by throwing data away. This is referred to as "lossy" compression, because you can never get the original uncompressed data back. Its compression is also optimized for photographs where high-contrast edges are uncommon. As stated in other answers, it's a bad choice for anything other than photographs.

Alpha/Transparency

Alpha refers to transparency, but it implies that there's more than one level of transparency. GIF has the ability to define transparent pixels, but it's either opaque or 100% transparent, and "transparent" gets used as one of the 256 colors. PNG and BMP have the ability to mark each pixel as opaque, transparent, or partially transparent, like a piece of colored glass. Most commonly, there are 256 levels of transparency, though PNG can actually have up to 65,536 levels. JPEG has no support for transparency.

Animation

Effectively, of these formats, only GIF has any support for animation. There are specifications for animation with PNG (MNG, APNG) and JPEG (MJPEG), but they are not widely supported. (APNG works in recent versions of Firefox and Opera.) In practice, most animations you see on web pages are implemented in Flash.

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APNG is gaining a lot of support. –  Phoshi Oct 10 '09 at 16:37
    
Sure enough. I hadn't noticed. –  wfaulk Oct 10 '09 at 17:00
    
Well, most modern browsers support it, but it's little known. IE8 doesn't support it, I don't think (but can read it as PNG, so displays the first frame) –  Phoshi Oct 10 '09 at 19:05
    
Great thought processing .. –  InfantPro'Aravind' Dec 17 '09 at 4:18
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+1 - Really great answer. –  boehj Mar 28 '12 at 1:39
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  • Use GIF if the image has few colors (like icons). Can also be used for animated images (like ad banners).
  • Use JPG if the image has many colors (like photos). JPEG is the same thing.
  • Use BMP if you want to save the image without compression. Much larger filesize!
  • Use PNG if you want to publish the image on the web and be up-to-date on modern standards. Pros: Suitable as modern replacement for both GIF and JPG, and is an open standard, and allows transparency. Cons: Not supported by older software, and file size can be larger than comparable GIF or JPG.
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+1 for practical considerations of when to use each. –  Andrew Coleson Oct 10 '09 at 17:42
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Be careful about using PNGs. As a lossless format, they're generally unsuited to photographs and the like, due to file size. Definitely not a "modern replacement" for all purposes. Transcoding from JPG to PNG would be really stupid. –  Paul McMillan Oct 10 '09 at 18:47
    
@Paul - I agree, it's certainly not useful for all purposes and in particular not for photos, but when used for web graphics it does replace JPG. –  Torben Gundtofte-Bruun Oct 10 '09 at 22:40
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I don't think there's ever a need for BPM nowadays. –  Arjan Oct 15 '09 at 11:22
    
@Arjan, there is need when you're working with low-tech customers (who still use Win2k, for instance). Plus, it's what Windows Paint defaults to, so it will be de facto standard for some time yet. –  Torben Gundtofte-Bruun Oct 15 '09 at 11:57
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enter image description here


BMP:

  • Old format. No loss of data.
  • Not compressed - Stores value of each pixel. Hence pictures of the same dimensions have same filesize (kilobytes/megabytes). E.g., 800×600 BMP images are always 1.37 MiB like the popular WinXP wallpaper "Bliss" rolling hills.
  • Transparency/translucency not supported
  • Not recommended for anything

JPG:

  • Lossy compression.
  • Loss amount can be set, e.g., while creating a graphic & saving in Photoshop.
  • Saving as higher quality means less loss of colours/depth and high filesize, and vice versa.
  • Transparency/translucency not supported
  • Recommended for photographs, not for graphics/icons

PNG:

  • Lossless compression (yeah, best of both WORDS/worlds)
  • Supports transparency AND translucency, both are different
  • Recommended for static graphics/icons, not for photographs

GIF:

  • Supports transparency but not translucency
  • Recommended for ANIMATED graphics/icons only
  • Maybe the moving photographs in frames in Harry Potter are GIFs :D
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BMP uses either raw bits with a small header, or Run-length Encoding. JPEG uses Discrete Cosine Transform. See the block at the bottoms of the Wikipedia articles for other compression/encoding algorithms.

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Me likey the PCX. Way back when decide to learn assembler, for my first program, I wrote a PCX viewer. It was quite educational. (I did not write a JPG viewer). :-D –  Synetech Feb 17 '12 at 3:58
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Simple guid:

  • For photographs, use:
    • Camera-specific raw formats if you have professional equipment and want to do a lot of post-processing
    • JPEG otherwise (for publishing photos on the web, you'll have to convert the raw formats to JPEG as well)
  • For anything with sharp edges, fine lines and few colors (such as screenshots or logos) use:
    • GIF if you're doing a webpage that has to support very old browsers (IE 6 mainly), or if you want to do simple animations
    • PNG otherwise
  • There is no good reason to use BMP, unless a specific program does not accept other formats.
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IE has supported PNG since some version 4.x (5 on Mac), but just not transparent PNG. –  Arjan Oct 15 '09 at 11:49
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IE6 actually even supports transparent PNG if it has GIF-like transparency. Only PNG with full alpha isn't supported. –  porneL Dec 27 '09 at 13:51
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Actually Alpha Transparency IS supported, provided it's an 8-bit PNG. Weird, but true. –  Django Reinhardt Jun 13 '11 at 20:13
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