What are the merits of using a particular image file format?

Question

If I edit an image file using some application like GIMP, Photoshop or MS Paint, while saving I will be asked to select the required file-format. There are different formats available, the common ones are JPEG, PNG and BMP, GIF and TIFF. With some programs, there are even more formats like JP2.

So which option should I select? What are the merits and demerits of using a particular file format?

I hope that my edit does not violate anythig that was said in "Is it gaming the system to edit a question you've also answered?" - If it does, feel free to roll it back. Intention of edit: It is a good question that had a title too specific (IMHO), especially since HEIF and other formats are starting to become widespread. — flolilo, Mar 16, 2019 at 14:52
@flolilolilo I don't think that is a problem here.. I am a little concerned that this will get less organic search traffic and that we will have to do more manual closing of duplicates, but, eh. — mattdm, Mar 16, 2019 at 20:59
@mattdm Sorry, I did not mean to introduce further labour here! I was just thinking that "should I use JPEG, BMP or PNG" left open the door for...well, all other codecs. If it is just me, then there is no need to keep it this way. — flolilo, Mar 16, 2019 at 21:03

Community · Accepted Answer · 2020-06-16 11:21:41Z

JPEG

JPEG is lossy, which means it compresses the image (in part) by discarding data. The data it discards is (normally) chosen to minimize the affect on the quality of the image, but it (virtually) always loses at least a little quality -- and depending on the quality level you choose, it can lose quite a bit. For most photographs it should be considered a display-only format -- once you've converted something to JPEG, you don't want to do any more editing on it. If you need to make changes, you re-start from some other format, make the changes, and do another JPEG conversion.

JPEG 2000, JPEG XR

There are newer versions of the JPEG specification. They define new forms of image compression that can generally give a better trade off between file size and image quality--your choice of the same quality with a smaller file, or better quality with roughly the same file size. They also support higher color resolution (e.g., 16 bits per channel and floating point formats to support high dynamic range). From a technical perspective, they're extremely attractive. The big disadvantage is that not nearly as many programs know how to read, display, manipulate, or write them.

HEIF

Like TIFF, HEIF is really a container format, which can contain images encoded with various methods (primarily h.265, but also h.264 and JPEG). It provides a better ratio of quality to file size than the original JPEG. Like TIFF (or GIF) you can package a whole sequence of pictures into a single file. Although there was considerable fanfare when HEIF was introduced in 2014, with many proclamations about how it was going to finally be the format that killed JPEG, most of the excitement seems to have fizzled without its displacing JPEG to any significant degree.

BPG

BPG is a format designed by the ever-prolific programmer Fabrice Bellard. It's similar to HEIF in basically being a container for an image encoded with h.265. The wrapper is a bit different, however, so the two aren't compatible with each other. From a photographic viewpoint, however, BPG has a fairly significant advantage: it directly supports embedding EXIF data into the image file.

Lossless JPEG

Although what we normally think of as JPEG is lossy, the JPEG specifications define file formats that use lossless compression as well. Since the compression is lossless, they don't usually produce nearly as small of files as normal JPEG compression can, but they actually do really well for lossless compression--much better than general-purpose compression like LZW or Huffman encoding normally even hope for on photographs. Like JPEG 2000 and JPEG XR, these work well, but suffer from lack of support.

GIF

GIF uses only lossless compression, but is limited to 8-bit (256) colors, which is quite limiting for photographs.

PNG

PNG was designed as a replacement for GIF, and mostly succeeds. It supports 24-bit color (8 bits each for red, green, and blue) and uses lossless compression. It has the color resolution necessary for photographs, but the compression it uses tends to be quite ineffective for most photographs, so files end up pretty large. The other big disadvantage of PNG is that it doesn't define a way to store EXIF (or similar) data, so if you use it to store photographs, you have to store the metadata separately. That can be fine for your own use, but means it'll generally be lost if you use it on a web page, or anything like that.

TIFF

TIFF is really a container format that allows you to insert various kinds of data into the container. While it's used primarily for images, it's really almost like a file system, so you could theoretically use it for almost any kind of data. This has a couple of consequences. One is that even if a program supports TIFF files, it may not support all TIFF files -- e.g., many don't support LZW-compressed images. In fact, few programs support all possible TIFF files. Another consequence is that TIFF tends to have a fair amount of overhead, and writing code to support TIFF (at all well) is a pain (which is why so many programs support it only incompletely).

BMP

BMP is basically just a Windows device independent bitmap written out to disk. It has only extremely limited support for compression (and most BMPs aren't compressed at all). Programs written for Windows can read/write BMP really easily, but there's not much else to recommend it (in particular, BMP files tend to be quite large for the amount of data being stored). BMP lacks any way to store EXIF (or similar) metadata. BMP is kind of like PNG, but more specific to Windows.

Conclusion

JPEG is useful as an output format (e.g., to display things on web pages it's good because it's compact, and virtually everybody can read it).

TIFF is frequently used as an intermediate format to (for example) store a file that might later be edited.

The 256-color limitation makes GIF pretty close to useless for photographs. BMP and PNG are basically harmless to the photograph itself, but can't store metadata, and the compression they use is rarely very effective for photographs (though storage prices are now low enough that quite a few people may not care much about that).

PNG actually supports 32bits, as it also supports 8 bits of alpha channel. Not that important for storing complete photographs, but if for example generating an image to be used on a web page, then the 8bit alpha channel could be really important. — Pete, Jun 11, 2011 at 10:05
@ClicketyRicket: I've edited to add a bit more information that I hope explains the situation better. — Jerry Coffin, Mar 15, 2019 at 20:31
@JerryCoffin Do you think you could add something about JPEG XR, and maybe HEIF? — mattdm, Mar 16, 2019 at 14:57

jrista · Accepted Answer · 2011-06-08 21:53:04Z

In general, I would say you probably want to save to a format that supports metadata unless you have a compelling reason to do otherwise. In that regard, jpeg and tiff are the two most common formats for photography outside of RAW+XMP or DNG.

I have used PNG in some of my online portfolios, as I've taken to rounding the corners of my scaled-down images for nicer exhibition and to do something to set my work apart from everyone elses. The down side of this is that PNG does not support metadata. This has limited me in a lot of respects, as most of the better online photo sites support automatic metadata extraction and display (i.e. Flickr).

To be more explicit...when exhibiting downscaled versions of your art online, such as on Flickr, DeviantArt, 1x, RedBubble, etc...it is probably best to use JPEG as your final output format. These files are good quality but very compact, and do support metadata. For long-term storage of originals, I would recommend RAW+XMP, DNG, or TIFF, as all of those formats do lossless compression and also keep metadata. TIFF might be the best choice for you if you are using Gimp. I have used RAW+XMP myself, as I like having my original raw files...but I have also considered converting everything to DNG to simplify file management.

flolilo · Accepted Answer · 2019-03-16 16:06:15Z

^{Prepare for an immense post - yes, this got out of hand...}

Obligatory xkcd:

xkcd #927 "Standards"

Unfortunately, there is no simple 'best' format. Some are very well supported, some offer extreme versatility, some offer lossless compression,...

The first part of this answer ("Features" & "Brief overview of the formats") will talk about technicalities, while the second part ("(Other) Things to consider") is more directed at the practical aspects of the choice of format.

Features:

^{Please note that it is almost impossible to include every hack to every format - e.g. GIFs can be saved without compression by ignoring the LZW table. Why do I not mention this below? Because 99% of all GIFs I ever encountered used LZW, because LZW today is a no-brainer in computation power, and because this post tries to clarify the situation for popular situations, not for ILM's R&D department. Photographers will use their files for archival, publishing and print, so these are the things I consider here.}

Information cross-checked between the respective Wikipedia articles, specifications, Wiki's comparison, and exiftool's metadata-support-list.

               |  Bits per  |                          |     Supported by 
 Codec | Lossy |  Channel   |   Metadata    | Channels |       Programs       | Good for (IMHO)
-------------------------------------------------------------------------------------------------
  BMP  |   n   |    <= 8    |      -        |   RGBA   | Most propr. & free   | Archival
  BPG  |   y   |   <= 14    |   EXIF+XMP    |   RGBA   |                      | 
  EXR  |   o   |   <= 32    |     y(?)      |  RGBAD   |                      | VFX workflow
  FLIF |   o*  |   <= 16    |   EXIF+XMP    |   RGBA   |                      | To be seen
  GIF  |   n   |   <= 8*    |      XMP      |   RGB    | Most propr. & free   | GIFs ;-)
  HEIF |   o*  |   <= 16    |   EXIF+XMP    | RGB(A/D) |                      | To be seen
  JPEG |   y*  |    <= 8    | EXIF+IPTC+XMP |   RGB    | ~ all propr. & free  | Online; Easy access
  JP2K |   o   |   <= 32    | EXIF+IPTC+XMP |   RGBA   |                      | 
  JXR  |   o   |   <= 32    | EXIF+IPTC+XMP |   RGBA   |                      | 
  PNG  |   n   |   <= 16    | EXIF+IPTC+XMP*|   RGBA   | Most propr. & free   | CAD-drawings; Online
  TGA  |   n   |    <= 8    |     y(?)      |   RGBA   |                      | 
  TIFF |   o   |   <= 32    |   EXIF+XMP    |   RGBA   | Most propr. & free   | Archival; Editing
  WebP |   o   |    <= 8    |   EXIF+XMP    |   RGBA   |                      |

^{Legend: o... Optional; n... not available; y... available; D... Depth; *...Look below at according text.}