Image 120.jpg
This is actually tricky, especially if you plan on returning an image url for use cases where you need to concatenate strings with the onerror condition image URL, e.g. you might want to programatically set the url parameter in CSS.
Image 120.jpg
The trick is that image loading is asynchronous by nature so the onerror doesn't happen sunchronously, i.e. if you call returnPhotoURL it immediately returns undefined bcs the asynchronous method of loading/handling the image load just began.
The AHFC Newsroom is AHFC's dedicated channel for providing company information such as images, videos and press releases to journalists, bloggers and other professional publishers. The site provides the latest as well as historical information about AHFC, and is also a guide for whom to contact for any media questions.The images and the videos cannot be used in any advertising or commercial context without a written permission from AHFC, Government Relations and Public Affairs. For high resolution versions, please contact Kalinda Kindle.
JPG, also known as JPEG, is a file format that can contain image with 10:1 to 20:1 lossy image compression technique. With the compression technique it can reduce the image size without losing the image quality. So it is widely used in web publishing to reduce the image size maintaining the image quality.
This document is intended for architects and developers building applications that share and consume digital images, particularly from cultural heritage institutions, museums, libraries and archives. Target applications include:
This specification concerns image requests by a client, but not management of the images by the server. It covers how to respond to requests that follow a particular URI syntax, but does not cover methods of implementation such as rotation algorithms, transcoding, color management, compression, or how to respond to URIs that do not conform to the specified syntax. This allows flexibility for implementation in domains with particular constraints or specific community practices, while supporting interoperability in the general case.
Implementations may use a pre-generated set of files served as static web resources and still enable rich user experiences. Dynamic image server implementations may provide additional functionality beyond the base level of compliance.
The term underlying image content is used to refer to the source image data. No assumptions are made about its format or structure. It might be derived from one or more source images but could also be dynamically generated.
The term full image is used to refer to the entire area of the underlying image content, with the pixel dimensions given in the image information document, and which is imagined as the starting point for image requests.
The scheme, server, prefix and identifier components of the information request must be identical to those for the image request described above for the image content that the image information document describes. The image information document is described in detail in the Image Information section.
All parameters described below are required for compliant construction of a IIIF Image API URI. The sequence of parameters in the URI must be in the order described below. The order of the parameters is also intended as a mnemonic for the order of the operations by which the service should manipulate the image content. Thus, the requested image content is first extracted as a region of the full image, then scaled to the requested size, mirrored and/or rotated, and finally transformed into the requested color quality and format. This resulting image is returned as the representation for the URI.
The region parameter defines the rectangular portion of the underlying image content to be returned. Region can be specified by pixel coordinates, percentage or by the value full, which specifies that the full image should be returned.
The size parameter specifies the dimensions to which the extracted region, which might be the full image, is to be scaled. With the exception of the w,h and ^w,h forms, the returned image maintains the aspect ratio of the extracted region as closely as possible. Sizes prefixed with ^ allow upscaling of the extracted region when its pixel dimensions are less than the pixel dimensions of the scaled region.
For all requests the pixel dimensions of the scaled region must not be less than 1 pixel or greater than the server-imposed limits. Requests that would generate images of these sizes are errors that should result in a 400 (Bad Request) status code.
In most cases, rotation will change the width and height dimensions of the returned image. The service should return an image that contains all of the image contents requested in the region and size parameters, even if the dimensions of the returned image file are different than specified in the size parameter. The image contents should not be scaled as a result of the rotation, and there should be no additional space between the corners of the rotated image contents and the bounding box of the returned image.
For rotations which are not multiples of 90 degrees, it is recommended that the client request the image in a format that supports transparency, such as png, and that the server return the image with a transparent background. There is no facility in the API for the client to request a particular background color or other fill pattern.
The default quality exists to support level 0 compliant implementations that may not know the qualities of individual images in their collections. It also provides a convenience for clients that know the values for all other parameters of a request except the quality (e.g. .../full/120,80/90/quality.png to request a thumbnail) in that a preliminary image information request that would only serve to find out which qualities are available can be avoided.
Regardless of level of compliance, services that make additional qualities beyond default available must list those qualities in the extraQualities property of the response to the Image Information Request. A request for an image with an unsupported quality value should return a 400 (Bad Request) status code.
A request for the color quality of an image must return an image. This image may be comprised solely of grayscale or bitonal pixels if this is all of the color information the server has available. The server should not include color in the extraQualities list in such cases, but a request for the color quality must not result in an error. Similarly, a request for the grayscale quality may return an image comprised solely of bitonal pixels.
The sequence of parameters in the URI is intended as a mnemonic for the order in which image manipulations are made against the underlying image content. This is important to consider when implementing the image service because applying the same parameters in a different sequence will often result in a different image being delivered.
It is possible to request the same image using different combinations of parameters. While it is useful for clients to be able to express their requests in a convenient form, there are several reasons why a canonical URI syntax is desirable:
In order to support the above requirements, clients should construct image request URIs using the following canonical parameter values where possible. Image servers may redirect the client to the canonical URI from a non-canonical equivalent.
The IIIF Image API is extensible within the Image Request URI Syntax through the addition of new parameter patterns for the region, size and rotation parameters, or new values for the quality and format parameters. Request information beyond the scope of the existing parameters could be passed to an image server as query parameters. Extension features should be described in the image information document following the guidelines in the Extra Functionality section.
Servers must support requests for image information. The response is a JSON document that includes technical properties about the full image. It may also contain rights information, and services related to the image.
The maxWidth, maxHeight, and maxArea parameters provide a way for image servers to express limits on the sizes supported for the image. If maxWidth alone, or maxWidth and maxHeight are specified then clients should expect requests with larger linear dimensions to be rejected. If maxArea is specified then clients should expect requests with larger pixel areas to be rejected. The maxWidth / maxHeight and maxArea parameters are independent, servers may implement either or both limits. Servers must ensure that sizes specified by any sizes or tiles properties are within any size limits expressed. Clients should not make requests that exceed size limits expressed.
The JSON objects in the tiles array have the properties in the following table. The width and height should be used to fill the size parameter, and be used together with the scaleFactors to compute the region parameter of the image requests. This is described in detail in the Implementation Notes.
The JSON response may have the preferredFormats property, which lists one or more format parameter values for this image service. This allows the publisher to express a preference for the format a client requests, for example to encourage use of a more efficient format such as webp, or to suggest a format that will give better results for the image content, such as lossless webp or png for line art or graphics.
If the publisher of this image requires additional information to be shown when it is viewed, the information should be provided by a Presentation API Manifest, as described in the Linking Properties section. 041b061a72