This version (2017/04/07 15:01) is a draft.
Approvals: 0/1

LTU engine/ON demand Description & User Guide

1. Introduction: Visual Search

Images finding images: LTU engine is the foundation for visual search: image matching, similarity search, and color search.

Visual search is using one image to find other images. Visual search based upon the content of an image, rather than based on textual information.

Two key technologies of visual search are image description and image search.

Image description (Indexation): The first step toward making an image searchable is to create a descriptor of the image content. LTU engine computes a visual signature for every image that describe its visual content in terms of color, shape, texture and many higher order visual features. These descriptors are also called image DNAs.

Image search: Image search is the comparison of one image signature with another, or with millions of other signatures. LTU's proprietary architecture includes a special comparison technology by which an image signature can be compared at extremely high speed with other image signatures.

The core data for LTU engine is the signature, also called the image DNA, not the image itself. Image signatures are presented in the “Create Application” section of the “Administrative Interface” guide below.


These principal functionalities are packaged in LTU engine, which provides the components necessary for creating and managing visual search applications, including JSON API and a comprehensive Administrative Interface.

2. Description: LTU engine/ON demand

LTU engine/ON demand is a hosted software platform that provides access to LTU Tech’s comprehensive image recognition functionalities. The LTU engine/ON demand platform is highly flexible and is designed to adjust and scale with changing demands.

A single account for LTU engine/ON demand can be used to add image recognition functionality to multiple applications.

The LTU engine/ON demand Administrative Console is accessed via. URL: https://www.ltu-engine.com/
See the Administrative Interface section below.

LTU engine/ON demand has the same Administrative Interface as the licensed version of LTU Tech software: LTU engine/server. Some aspects unique to LTU engine/ON demand found in comments marked with this symbol: :!:

JSON API: the JSON API is the recommended API for new applications. The licensed version of LTU engine includes the JSON API, which facilitates the porting of applications from LTU engine/ON demand to LTU engine/server. Query examples in the JSON API documentation generally reference LTU engine/server. :!: LTU engine/ON demand users will know to adjust the query examples to the proper /ON demand references.

Below is a quick checklist to help prepare for the integration of LTU engine/ON demand.

  • Signature type - What feature(s) needed? (similarity, matching, color)
  • Storage
    • Estimate the number of images that will be included for the application
    • Estimate the image volume changes per month on this application
  • Search
    • Estimate number of searches per month
  • Development
    • List the public IP addresses of all machines that will make direct calls to the API interface.
    • Launch sample code provided by LTU Tech to check that everything works
    • Start development and unit test
    • Validate (pay attention at the refresh delay per application)
    • Empty the database and start loading content for the application
  • Production
    • Monitor the number of queries per month (also available on the LTU engine/ON demand administrative console)
    • Continuously evaluate the capacity used monthly in terms of queries and image database volume

3. Glossary

  • Application: An application database that contains image DNA’s (the image database), meta-information and various settings (including the functionality the application was created for – matching or similarity).
  • Application Key: Each application has a unique application key that is used to access the application.
  • Bounce: Taking a single DNA from an image database and comparing it to all DNA in the same image database.
  • Color Weight: Using LTU Tech’s similarity algorithm you can control the return results based on color weight. Using color weight, the search can be weighted on the colors of the entire image, entirely on the shapes of the image or any combination of the two.
  • Duplicate & Clone: A duplicate image is one that is where exactly all pixels have the same value as in the comparison image, any modification such as coloring or resizing makes the image a clone.
  • DNA & Signature: When an image has been indexed a binary string is generated called an image DNA or signature.
  • Global Matching: A global match detects if two images are exactly or very nearly the same.
  • Enrollment: Reference to the entire process of taking an image, indexing it to generate a DNA, storing the DNA and keywords, generating and storing a thumbnail and reference image to an application.
  • Image Database: Each application has its own database storage, in which a DNA is stored
  • Image DNA Type: Each DNA is designed for a specific feature (matching or similarity).
  • Image_ID: The image_id is a unique key to the client’s image within an application and for a client. The image_id can be thought of as a foreign key to the client’s database. The system will not accept duplicate image_id’s.
  • Indexation: The act of processing an image by an algorithm to generate a DNA.
  • Keywords: Each image entity may have a set of keywords (string) associated with it. These keywords are helpful for aiding and enhancing searches. Note: keywords may be duplicated across multiple images within a single image database but should not be duplicated on one image (eg. acceptable ‘red,dog,bed’, unacceptable ‘red,red,red,dog,bed’).
  • Local Matching: Local matching is able to find matching sub-sections of two images or images of the same object.

4. Administrative Interface

LTU Engine Administrative Interface

Both LTU engine /server and LTU engine /ON demand share the same Administrative Interface.

However, there are certain differences in

  • feature availability
  • API syntax

In this document, these differences are noted by text marked with this symbol: :!:

Creating new and managing existing applications are possible via the Administrative Interface of LTU engine/server. However, application paramenters should be modified only as instructed by LTU Tech support.

Monitoring the performance of applications and authorizing IP access have been the primary purpose of the LTU engine/ON demand administrative interface.

The creation and configuration of applications remains the responsibility of LTU Tech support.

New features were added to the Administrative Interface in July 2012: These include the Image Management tab which is detailed in this document.

Also, Visual Query Logs may be activated on individual applications (to activate Visual Query Logs, please contact LTU Tech support.

  • Image Management - Browse Images
  • Image Management - Bounce Search with Display of Matching Zones
  • Image Management - Batch Processes via the Administrative Interface
  • Statistics - Numeric and Graphical
  • Statistics - Visual Query Logs


Manage Applications - Applications Dashboard

The Dashboard displays information about all applications (Active and Inactive)

  • Active Applications Includes graphic indicators of the status of each application.
  • Inactive Applications Information on applications which are still present on the disk storage system but are not loaded into memory, thus not available for queries
  • Get Image ID's For creation and download of a .csv file containing the image ID's and keywords for all images in the application.


Application Parameters - Display and Update




Reminder: Application parameters should not be changed unless advised by LTU Tech support.

  • Name: Application Name may be changed here at any time without affecting operations. Application names should contain no accents or special characters. Spaces are permitted. Maximum name length: 256 charcters.
  • Status: Unchecking this box will make the application Inactive. Image signatures are unloaded from system memory.
  • Application Search DNA: Different from the “Application DNA”, the “Application Search DNA” is a parameter for certain types of Image Matching applications. It functions on external images, creating a larger, more detailed image signature, which is effective in applications where query images may be of varying quality, such as mobile applications.

For information on signatures, see section Create Application

  • Color Weight Applicable only to “Image Similarity” applications.“Color Weight” is the default color weight used when not specified in the query (SearchImageByDna or SearchImageByUpload). Default: “50” (balance between Color and Shape). Weighted for form: “0”. Weighted for color: '100“.
  • Save query logs days This affects the Batch search reports as well as invididual queries.
  • Number of Results: Default number of results when not specified in the query. Applies to API queries as well as to queries via the Admin Interface (number of bouce results, displayed, for example).
  • Retrieval Threshold: Threshold on retrieval results. Image with a score superior to this threshold will NOT be returned. -1 means no threshold.
  • Comments: Any comments describing specifics of the application.

Application Status

  • Last Add: Time elapsed since last AdImage, whether effected via the API or via the Admin Interface.
  • Last Search: Time elapsed since last SearchImage, whether effected via the API or via the Admin Interface.
  • Number of Kimas: Number of kima processes associated with this application. This number is automtically adjusted by the system may not be modified via the Admin Interface.
  • Images: Total number of images in the application.
  • Keywords: Since individual images may have multiple keywords, this number may be larger than the number of images.
    Reminder - for images enrolled via the Admin Interface (Image Management, batch process, Add images) keywords are automatically generated if the submitted zip file is organized by subdirectories. Keywords are generated for all levels of the file hierarchy.

    Also see the API Methods section (AddImage and SearchImage…) for additional information about keywords.

Advanced Management Status Information

  • Update messages and codes: Values are:
  1. the application has never been updated by the manager process
  2. the application is currently queued for update
  3. an update is currently running for the application
  4. an update has already been run for this application (normal state)
  5. an update failed
  • Next update: Applications are automatically when necessary
  • Last generation: “Generation” means update of the application.

Advanced Actions: Update, Rebuild, Reload

Unless instructed by LTU Tech support, it is generally unnecessary to perform these actions.

Note: None of the following actions deletes data from disk storage.

These actions concern the reloading of data elements into system memory. An application is temporarily disabled during the execution of these functions.

  • Update Application: Adds new elements, such as new image signatures, to system memory. However, this is done automatically during standard update procedures, such as AddImage or addImageBatch.
  • Rebuild Application: Unload and Reload: unloads the application from system memory, and completely reloads the application from the database.
  • Reload Configuration As distinguished from application content (which is updated or reloaded by Update and Rebuild Application), this action reloads application parameters. However, this is done automatically “Apply Modifications” is selected after application parameters are modified.

Application information (display only)

  • Creation Date: Date creation of the application.
  • Application Key: The application key is generated at aplication creation and may not be changed.
  • Application DNA Type: Displayed in long form: 70001000 = 70.1.1.
    Application DNA type cannot be changed once an application is created. To change a DNA type for a set of images, a new application must be created, and the images must be indexed in the new application.
  • Application Type: The category (Image Matching, Image Similarity) of the Application Type selected at application creation.
  • Folder path: This is the location of the images of an application.
  • Database Location: For information only; significant only for special configurations involving a database on a separate server.
  • Retrieval Threshold: Retrieval threshold currently in effect. May be modified via the “Application parameters” form, if so advised by LTU Tech support.

Create Application

:!: LTU engine/server only. For LTU engine/ON demand, applications are created by LTU Tech support.

  • Name: Application names should be limited to fewer than 256 characters, with no accents or special characters. Spaces are permitted.
  • Application Type: The choice of “Image matching” or “Image similarity” determines which signatures will be displayed as available options for the application.
  • Application DNA: Explained here following:

Matching Signatures

Type Signature ID Options Signature Size (bytes)
In Memory
Use and Characteristics
Media Monitoring 65.0.0 Flip - Text 2056 Media Monitoring - high speed indexation and retrieval in large applications. Recommended
Mobile Matching 71.2.0 Asymetric Retrieval 14000 (average) Mobile without text - more robust to text
Mobile Matching 71.2.2 Asymetric Retrieval 14000 (average) Mobile - sensitive to text
Brand Monitoring 71.2.4 Asymetric Retrieval 14000 (average) Brand Monitoring - sensitive to text


Asymetric Retrieval: Asymetric Retrieval is automatically activated for applications whose signature includes the option. Asymetric Retrieval applies to external queries (SearchByUpload): a large temporary signature (not stored in the application) is calculated for the external query image, which is then compared with the application images.

Similarity Signatures

Type Signature ID Options Signature Size (bytes)
In Memory
Use and Characteristics
Similarity 4.2.0 query weighting Color/Form 1340 Image similarity search

Color Signatures

Type Signature ID Options Signature Size (bytes)
In Memory
Use and Characteristics
Color 8.0.0 query weighting Color/Form 897 Dominant colors signature
Color without uniform background 8.1.0 query weighting Color/Form 897 Same as 8.0 but with uniform background removal

Browse Images

The Browse Images feature of Image Managment allows a display of all images present in an application.

Images are arranged chronologically (images last added are displayed first).

Page controls allow browsing the entire database

Browse Images - Search Image

Any image selected via the Browse Images page may be used as a search query:


Clicking on a result image shows a display of the matching zone.

Run Batch Process

Add Images

For the selected application, images may be added by uploading a zip file. Filenames must be unique across the zip file, since the filename is used as the image id.

Keywords: Keywords may be associated with images added via this process. Folder names are used as keywords for the images. This may include multiple levels. In the example below, during indexation, images are assigned keywords according to where the image files are found in the folder directory tree.

A batch add process may be designated by a Report Name. The report is timestamped and may be accessed later to know the number of images enrolled.

Search Images

Batches of images may be submitted as queries. The batch search may be designated by a Report Name. The batch search report maybe accessed later, and includes displays of the query images and the results.

Previous Batch Processes

Batch processes described above are accessed via these links.

Advanced Usage: Test API Queries

This page provides a simple way to understand the functioning of the principal queries. For the selected application, query parameters may be entered via the screen interface. The display then shows both the json response and,if applicable, the associated images.

The Statistics tab gives access to numeric and graphical measures of system utilization.

It also provides access to Visual Query Logs, which permit the viewing of all search queries effected on the system. The logs display the query image and the results, ranked according to proximity score.


For applications using one of the Matching signatures, the Query Logs view permits the viewing of teh “Matching Zone”. Clicking on any one of the result images displays the Matching Zone for the query image and the result image:


5. Image Formats Supported

Any image sent to LTU engine must be in of the following formats:

  • PNG
  • GIF
  • JPEG, JPG
  • BMP

You will need to convert your images to one of these formats before sending them to LTU engine.

  • We recommend using images of 512 x 512 pixels when adding or searching images
  • Images data/file size should not be smaller than 50kb



  • Images can be converted to gray