The Base64 Image Converter BETA Features coming soon
Some applications that use URLs also have a need to embed (small) media type data directly inline. This document defines a new URL scheme that would work like 'immediate addressing'. The URLs are of the form: data:[<mediatype>][;base64],<data>
The <mediatype> is an Internet media type specification (with optional parameters.) The appearance of ";base64" means that the data is encoded as base64. Without ";base64", the data (as a sequence of octets) is represented using ASCII encoding for octets inside the range of safe URL characters and using the standard %xx hex encoding of URLs for octets outside that range. If <mediatype> is omitted, it defaults to text/plain;charset=US-ASCII. As a shorthand, "text/plain" can be omitted but the charset parameter supplied.
The "data:" URL scheme is only useful for short values. Note that some applications that use URLs may impose a length limit; for example, URLs embedded within anchors in HTML have a length limit determined by the SGML declaration for HTML [RFC1866]. The LITLEN (1024) limits the number of characters which can appear in a single
attribute value literal, the ATTSPLEN (2100) limits the sum of all lengths of all attribute value specifications which appear in a tag, and the TAGLEN (2100) limits the overall length of a tag.
dataurl := "data:" [ mediatype ] [ ";base64" ] "," data mediatype := [ type "/" subtype ] *( ";" parameter ) data := *urlchar parameter := attribute "=" value
Mobile Web Application Best Practices
Include Background Images Inline in CSS Style Sheets
Visual effects (e.g. background images and gradients) are often used to improve the look and feel of an application. These can be included in CSS as base64 encoded strings in order to avoid an additional HTTP request
Note that base64 encoding adds around 10% to the image size after gzip compression and this additional cost should be weighed against the benefits of fewer requests.
Background images can be encoded using the data URI scheme: url('data:image/png;base64, [data])
[ CSS ] Requires: RFC2397 data uri support.
The data URI scheme is a URI scheme (Uniform Resource Identifier scheme) that provides a way to include data in-line in web pages as if they were external resources. This technique allows normally separate elements such as images and style sheets to be fetched in a single HTTP request rather than multiple HTTP requests, which can be more efficient.
Data URIs tends to be simpler than other inclusion methods, such as MIME with cid or mid URIs. Data URIs are sometimes called Uniform Resource Locators, although they do not actually locate anything remote. The data URI scheme is defined in RFC 2397 of the Internet Engineering Task Force (IETF).
In browsers that fully support Data URIs for "navigation", Javascript generated content can be provided as file "download" to the user, simply by setting window.location.href to a Data URI. One example is the conversion of HTML tables to downloadable CSV using a Data URI like this: 'data:text/csv;charset=UTF-8,' + encodeURIComponent(csv), where "csv" has been generated by Javascript.
The IETF published the data URI specification in 1998[1] as Proposed Standard on the IETF Standards Track, and hasn't progressed it since. The HTML 4.01 specification refers to the data URI scheme,[2] and data URIs have now been implemented in most browsers.
As of March 2012, Data URIs are supported by the following web browsers:
object (images only)imginput type=imagelink (data URI must be base64 encoded)background-image, background, list-style-type, list-style and similar.multipart/alternative or message/rfc822) to provide greater complexity such as metadata, data compression, or content negotiation.data:[<MIME-type>][;charset=<encoding>][;base64],<data>
The encoding is indicated by ;base64. If it's present the data is encoded as base64. Without it the data (as a sequence of octets) is represented using ASCII encoding for octets inside the range of safe URL characters and using the standard %xx hex encoding of URLs for octets outside that range. If <MIME-type> is omitted, it defaults to text/plain;charset=US-ASCII. (As a shorthand, the type can be omitted but the charset parameter supplied.)
Some browsers (Chrome, Opera, Safari, Firefox) accept a non-standard ordering if both ;base64 and ;charset are supplied, while Internet Explorer requires that the charset's specification must precede the base64 token.
We have found many good tools for reducing image size. Often times these tools are specific to particular image formats and work much better in certain circumstances than others. To "smush" really means to try many different image reduction algorithms and figure out which one gives the best result.
These are the algorithms currently in use:
Value Encoding Value Encoding Value Encoding Value Encoding
0 A 17 R 34 i 51 z
1 B 18 S 35 j 52 0
2 C 19 T 36 k 53 1
3 D 20 U 37 l 54 2
4 E 21 V 38 m 55 3
5 F 22 W 39 n 56 4
6 G 23 X 40 o 57 5
7 H 24 Y 41 p 58 6
8 I 25 Z 42 q 59 7
9 J 26 a 43 r 60 8
10 K 27 b 44 s 61 9
11 L 28 c 45 t 62 +
12 M 29 d 46 u 63 /
13 N 30 e 47 v
14 O 31 f 48 w (pad) =
15 P 32 g 49 x
16 Q 33 h 50 y
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It's very simple - you read the protocol and write the code. -Bill Joy
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