{WebTwainObject} Buffer Manage

The properties and methods on this page live in the namespace {WebTwainObject}. {WebTwainObject} denotes the WebTwain instance. Learn about how to create a web twain object.

All APIs on this page support Android Service from version 18.2 except IsBlankImageAsync().

Methods

Properties

Events

IndexToImageID()

Return the imageId of an image specified by the index.

Syntax

IndexToImageID(index: number): string;

Parameters

index: The index of the image.

Availability

ImageIDToIndex()

Return the index of an image specified by the imageId.

Syntax

ImageIDToIndex(imageId: string): number;

Parameters

imageId: The imageId of the image.

Availability

Usage notes

An imageId is unique and won’t change. It’s a better way to keep track of an image than the index which changes easily.

RenameTag()

Rename a tag.

Syntax

RenameTag(oldTag:string, newTag:string): boolean;

Parameters

oldTag: Specify the tag to change.

newTag: Specify the new tag name.

Availability

RemoveTag()

Remove the specified tag from one or more images(if not specified, remove from all).

Syntax

RemoveTag(tagName: string, indices?: number[]):boolean

Parameters

tagName: Specify the tag to be removed.

indices: Specify the index.

Availability

Usage Notes

If the index is not specified, the tag will be removed from all images. If the index is specified, the tag will be removed from the specified image(s).

GetTagList()

Return the status of all current tags.

Syntax

GetTagList(): TagInfo[];

Arguments

TagInfo: Please refer to TagInfo.

Availability

ClearImageTags()

Remove all tags from the specified image.

Syntax

ClearImageTags(index: number): boolean;

Parameters

index: Specify the image.

Availability

FilterImagesByTag()

Filter images by the specified tag.

Syntax

FilterImagesByTag(tag: string): boolean;

Parameters

tag: The tag used as the filter. If nothing or an empty string is used, the filter is cleared.

Availability

ClearFilter()

Stop filtering images by tag. Return an array of UUID of images under the viewer.

Syntax

ClearFilter(): number[];

Availability

SetDefaultTag()

Set a default tag for newly incoming images.

Syntax

SetDefaultTag(tag: string): boolean;

Parameters

tag: Specifies the tag.

Availability

TagImages()

Add a tag to specified images.

Syntax

TagImages(indices: number[], tag: string): boolean;

Parameters

indices: Specifies images to be tagged.

tag: Specify the tag.

Availability

GetImageBitDepth()

Return the pixel bit depth of the specified image.

Syntax

GetImageBitDepth(index: number): number;

Parameters

index: Specify the image.

Availability

GetImageHeight()

Return the height (in pixels) of the specified image.

Syntax

GetImageHeight(index: number): number;

Parameters

index: Specify the image.

Availability

GetImageWidth()

Return the width (in pixels) of the specified image.

Syntax

GetImageWidth(index: number): number;

Parameters

index: Specify the image.

Availability

GetImageXResolution()

Return the horizontal resolution of the specified image.

Syntax

GetImageXResolution(index: number): number;

Parameters

index: Specify the image.

Availability

GetImageYResolution()

Return the vertical resolution of the specified image.

Syntax

GetImageYResolution(index: number): number;

Parameters

index: Specify the image.

Availability

GetSkewAngle()

Return the skew angle of the specified image.

Syntax

GetSkewAngle(
    index: number
): number;

// Call this API asynchronously to avoid blocking the browser's main thread 
GetSkewAngle(
    index: number,
    successCallback: (angle: number) => void,
    failureCallback: (errorCode: number, errorString: string) => void
): void;

Parameters

index: Specify the image.

successCallback: A callback function that is executed if the request succeeds.

• angle: The skew angle.

failureCallback: A callback function that is executed if the request fails.

• errorCode: The error code.
• errorString: The error string.

Availability

GetSkewAngleEx()

Return the skew angle of the specified rectangle on the specified image.

Syntax

GetSkewAngleEx(
    index: number,
    left: number,
    top: number,
    right: number,
    bottom: number
): number;

// Call this API asynchronously to avoid blocking the browser's main thread 
GetSkewAngleEx(
    index: number,
    left: number,
    top: number,
    right: number,
    bottom: number,
    successCallback: (angle: number) => void,
    failureCallback: (errorCode: number, errorString: string) => void
): void;

Parameters

index: Specify the image.

left: The x-coordinate of the upper-left corner of the rectangle.

top: The y-coordinate of the upper-left corner of the rectangle.

right: The x-coordinate of the lower-right corner of the rectangle.

bottom: The y-coordinate of the lower-right corner of the rectangle.

successCallback: A callback function that is executed if the request succeeds.

• angle: The skew angle.

failureCallback: A callback function that is executed if the request fails.

• errorCode: The error code.
• errorString: The error string.

Availability

Usage notes

After you get the skew angle of an image, you can rotate it with the method Rotate() to perform deskewing.

GetImageSize()

Calculate the size in bytes of the specified image assuming it’s resized to the given dimensions.

Syntax

GetImageSize(index: number, width: number, height: number): number;

Parameters

index: Specify the image.

width: Specify the width.

height: Specify the height.

Availability

GetImageSizeWithSpecifiedType()

Calculate the size in bytes of the specified image assuming an expected file type.

Syntax

GetImageSizeWithSpecifiedType(index: number, type: Dynamsoft.DWT.EnumDWT_ImageType | number): number;

Parameters

index: Specify the image.

type: Specify the expected file type. Please refer to Dynamsoft.DWT.EnumDWT_ImageType.

Availability

GetSelectedImagesSize()

Calculate the size in bytes of all selected images assuming an expected file type.

Syntax

GetSelectedImagesSize(type: Dynamsoft.DWT.EnumDWT_ImageType | number): number;

Parameters

type: Specify the expected file type. Please refer to Dynamsoft.DWT.EnumDWT_ImageType.

Availability

Usage notes

If the calculation fails, -1 is returned.

GetImagePartURL()

Return the internal URL of the specified image.

Syntax

GetImagePartURL(index: number): string;

GetImagePartURL(index: number, width: number, height: number): string;

Parameters

index: Specify the image.

width: The width of the image (>150 px).

height: The height of the image (>150 px).

Availability

Usage notes

The returned URL looks like this: ‘dwt://dwt_trial_13000404/img?id=306159652&index=0&t=1502184632022’.

You get the original size (a, b) of the image in PNG format in Service Mode

• if either width or height is not set or
• if either width or height is set to -1 or
• if either width or height is larger than the original width or height

Otherwise, you get the image with the specified width (x) or height (y) while keeping the same aspect ratio: if x/a < y/b, return the image (x, b*x/a); if x/a > y/b, return the image (a*y/b, y)

GetImageURL()

Return the direct URL of the specified image.

Syntax

GetImageURL(index: number): string;

GetImageURL(index: number, width: number, height: number): string;

Parameters

index: Specify the image.

width: The width of the image (>150 px).

height: The height of the image (>150 px).

Availability

Usage notes

The returned URL looks like this: “https://127.0.0.1:18623/dwt/dwt_17110818/img?id=795151779&index=1&t=1640936181588”.

You get the original size (a, b) of the image in PNG format in Service Mode

• if either width or height is not set or
• if either width or height is set to -1 or
• if either width or height is larger than the original width or height

Otherwise, you get the image with the specified width (x) or height (y) while keeping the same aspect ratio: if x/a < y/b, return the image (x, b*x/a); if x/a > y/b, return the image (a*y/b, y)

SelectAllImages()

Select all images and return the indices. Viewer will be scrolled to the last image.

Syntax

SelectAllImages(): number[];

Availability

SelectImages()

Select the specified images.

Syntax

SelectImages(indices: number[]): boolean;

Parameters

indices: Specify one or multiple images

Availability

MoveImage()

Change the position of an image in the buffer.

Syntax

MoveImage(from: number, to: number): boolean;

Parameters

from: Specify the original position by index.

to: Specify the target position by index.

Availability

SwitchImage()

Exchange the positions of two images.

Syntax

SwitchImage(index1: number, index2: number): boolean;

Parameters

index1: Specify the 1st image.

index2: Specify the 2nd image.

Availability

RemoveImage()

Remove the specified image.

Syntax

RemoveImage(index: number): boolean;

Parameters

index: Specify the image.

Availability

RemoveAllImages()

Remove all images.

Syntax

RemoveAllImages(): boolean;

Availability

RemoveAllSelectedImages()

Remove all selected images.

Syntax

RemoveAllSelectedImages(): boolean;

Availability

CurrentImageIndexInBuffer

Return the index of the current image in the buffer or set the image specified by index as the current image.

Syntax

CurrentImageIndexInBuffer: number;

Availability

HowManyImagesInBuffer

Return how many images are held in the buffer

Syntax

readonly HowManyImagesInBuffer: number;

Availability

MaxImagesInBuffer

Return or set how many images can be held in the buffer.

Syntax

MaxImagesInBuffer: number;

Availability

Usage notes

When acquiring images and the number of images goes beyond the value set to MaxImagesInBuffer, new images will replace old images starting from the 1st one.

SelectedImagesIndices

Return the indices of the selected images.

Syntax

readonly SelectedImagesIndices: number[];

Availability

SelectionRectAspectRatio

Specify a aspect ratio to be used when selecting a rectangle on an image.

Syntax

SelectionRectAspectRatio: number;

Availability

BlankImageCurrentStdDev

Return the deviation of the pixels in the current image.

Syntax

readonly BlankImageCurrentStdDev: number;

Availability

Usage notes

This property is only valid after IsBlankImageExpress() or IsBlankImage() is called.

BlankImageMaxStdDev

Return or set the maximum deviation of the pixels in an image which is used to determine whether the image is blank.

Syntax

BlankImageMaxStdDev: number;

Availability

Usage notes

[0, 100] is the interval of allowed values, inclusive. 0 gives a single-color image. The default value is 1.

This property is only valid before IsBlankImageExpress() is called.

BlankImageThreshold

Returns or sets the dividing line between black and white.

Syntax

BlankImageThreshold: number;

Availability

Usage notes

[0, 255] is the interval of allowed values, inclusive. The default value is 128. This property is only valid before IsBlankImageExpress() is called.

BufferMemoryLimit

Return or set how much physical memory is allowed for storing images currently loaded in Dynamic Web TWAIN. Once the limit is reached, images will be cached on the hard disk.

Syntax

BufferMemoryLimit: number;

Availability

Usage notes

Set this property only when you have a very small physical memory (< 2GB) or a very big one (>4GB). The more memory is allowed, the better the performance will be. The default value is set to 800 (MB), anything beyond 800MB gets compressed, encrypted and cached on the local disk.

All cached data is encrypted and can only be read by Dynamic Web TWAIN and it will be destroyed when it is no longer used.

IsBlankImage()

Check whether the specified image is blank.

Syntax

IsBlankImage(index: number): boolean;

Parameters

index: Specify the image.

Availability

IsBlankImageAsync()

Check whether the specified image is blank.

Syntax

IsBlankImageAsync(index: number, 
  options?: {
    minBlockHeight?: number,
    maxBlockHeight?: number,
    }
): Promise<boolean> ;

Parameters

index: Specify the image in buffer to be analyzed.

minBlockHeight: Minimum height of mark to be detected. Default value: 20

maxBlockHeight: Maximum height of mark to be detected. Default value: 30

Availability

Usage Notes This API uses a different algorithm than the one used in IsBlankImage() and IsBlankImageExpress(), which allows you to judge a page as not blank if it has marks within a defined size. If the mark on the page satisfies the comparison parameters, then the page will be deemed not blank.

Example: The mark on the page is 11 pixels tall, minBlockHeight is set to 9 pixels and maxBlockHeight is set to 13 pixels, the page will be marked as not blank.

IsBlankImageExpress()

Check whether the specified image is blank.

Syntax

IsBlankImageExpress(index: number): boolean;

Parameters

index: Specify the image.

Availability

Usage notes

IsBlankImage() is more accurate than IsBlankImageExpress() but it works slower.

BlankImageCurrentStdDev should be read after either IsBlankImage() or IsBlankImageExpress().

If you believe an image should be blank but IsBlankImage() or IsBlankImageExpress() is returning false, you can read BlankImageCurrentStdDev for that image and then set a bigger value to BlankImageMaxStdDev.

Both BlankImageCurrentStdDev and BlankImageMaxStdDev range from 0 to 100.

If the image is not blank and it is not black and white, IsBlankImage() or IsBlankImageExpress() may return true. In that case, you can increase the BlankImageThreshold value so that the image is not detected as blank.

IfAllowLocalCache

Return or set whether the feature of disk caching is enabled.

Syntax

IfAllowLocalCache: boolean;

Availability

Usage notes

The default value of IfAllowLocalCache is true. When the property is true, you can scan as many images as you want as long as you have a big enough disk.
The default threshold is set to 800 (MB), anything beyond 800MB gets compressed, encrypted and cached on the local disk.
If necessary, you can set the threshold using BufferMemoryLimit for better performance.
All cached data is encrypted and can only be read by Dynamic Web TWAIN and it will be destroyed when it is no longer used.

OnBufferChanged

An enhanced callback triggered when a change occurs in the buffer.

Syntax

RegisterEvent('OnBufferChanged',
    function (bufferChangeInfo: BufferChangeInfo) {}
): boolean;

Parameters

bufferChangeInfo: Details about the buffer change. Please refer to BufferChangeInfo.

Availability

Usage notes

Action types include

• add: New pages are added to the buffer.
• remove: The existing pages are removed.
• modify: The existing pages are modified.
• shift: The existing pages are reordered or the selected pages are changed.
• filter: The existing pages are filtered by a tag.

OnBitmapChanged

A built-in callback triggered when the current image in buffer is changed like flipped, cropped, rotated, etc. or a new image has been acquired.

Syntax

RegisterEvent('OnBitmapChanged',
    function (
        indices: number[],
        type: number,
        index: number
    ) {}
): boolean;

Parameters

indices: Array of the changed index(indices).

type: Operation type. 1 means new image(s) were added at the tail, 2 means image(s) were inserted before the current index, 3 means image(s) are deleted, 4 means image(s) are modified,

index: Index of the current image.

Availability

Example

DWTObject.RegisterEvent(
  "OnBitmapChanged",
  function (updatedIndices, operationType, currentIndex) {
    console.log(updatedIndices);
  }
);

OnTopImageInTheViewChanged

A built-in callback triggered when the top index currently displayed in the viewer changes.

Syntax

RegisterEvent('OnTopImageInTheViewChanged',
    function (index: number) {}
): boolean;

Parameters

index: Index of the current image.

Availability

Usage notes

This API does not work if the view mode of the viewer is set to -1 by -1.

OnIndexChangeDragDropDone

A built-in callback triggered when images in the buffer are dragged to new positions.

Syntax

RegisterEvent('OnIndexChangeDragDropDone',
    function (indexPairs: Pair[]) {}
): boolean;

Pair: [from: number, to: number];

Parameters

indexPairs: The list of index changes.

Availability

GetTagListByIndex()

Return the tag(s) of a specified image.

Syntax

GetTagListByIndex(index: number):string[]

Parameters

index: Index of the image.

Availability

Example

DWTObject.GetTagListByIndex(0);

CopyToDocumentAsync()

Copy specified images to another document.

Syntax

CopyToDocumentAsync(from: string, to: string): Promise<void>;

CopyToDocumentAsync(from: string, to: string, sourceIndices: number[]): Promise<void>;

CopyToDocumentAsync(from: string, to: string, targetIndex: number): Promise<void>;

CopyToDocumentAsync(from: string, to: string, sourceIndices: number[], targetIndex: number): Promise<void>;

Parameters

from: The source document name.

to: The destination document name.

sourceIndices: The indices of the images to be copied.

targetIndex: The index at which the source images should be inserted into the new document. If not specified, the images will be appended to the destination document.

Availability

Example

DWTObject.CreateDocument("Document1");
DWTObject.CreateDocument("Document2");
DWTObject.OpenDocument("Document1");
await DWTObject.SelectSourceAsync();
await DWTObject.AcquireImageAsync({   //scan 5 Images
        IfCloseSourceAfterAcquire: true 
    });
await DWTObject.CopyToDocumentAsync("Document1", "Document2", [0,1]);
DWTObject.OpenDocument("Document2");

CreateDocument()

Create a document for the scanned image(s).

Syntax

CreateDocument(documentName:string):boolean;

Parameters

documentName: Specify the document name.

Availability

Example

//Save the scanned image(s) under 'Document1'.
DWTObject.CreateDocument("Document1");
DWTObject.OpenDocument("Document1"); //Need to call OpenDocument after CreateDocument.
DWTObject.AcquireImage(successCallback, failureCallback);
function successCallback() {
  console.log("successful");
}
function failureCallback(errorCode, errorString) {
  alert(errorString);
}

MoveToDocumentAsync()

Move specified images to another document.

Syntax

MoveToDocumentAsync(from: string, to: string): Promise<void>;

MoveToDocumentAsync(from: string, to: string, sourceIndices: number[]): Promise<void>;

MoveToDocumentAsync(from: string, to: string, targetIndex: number): Promise<void>;

MoveToDocumentAsync(from: string, to: string, sourceIndices: number[], targetIndex: number): Promise<void>;

Parameters

from: The source document name.

to: The destination document name.

sourceIndices: The indices of the images to be moved.

targetIndex: The index at which the source images should be inserted into the new document. If not specified, the images will be appended to the destination document.

Availability

Example

DWTObject.CreateDocument("Document1");
DWTObject.CreateDocument("Document2");
DWTObject.OpenDocument("Document1");
await DWTObject.SelectSourceAsync();
await DWTObject.AcquireImageAsync({   //scan 5 Images
        IfCloseSourceAfterAcquire: true 
    });
await DWTObject.MoveToDocumentAsync("Document1", "Document2", [0,1]);
DWTObject.OpenDocument("Document2");

OpenDocument()

Use the specified document for the scanned image(s)

Syntax

OpenDocument(documentName:string):boolean;

Parameters

documentName: Specify the document name.

Availability

Example

//Save the scanned image(s) under 'Document2'.
DWTObject.CreateDocument("Document1");
DWTObject.CreateDocument("Document2");
DWTObject.CreateDocument("Document3");
DWTObject.OpenDocument("Document2"); //Need to call OpenDocument after CreateDocument.
DWTObject.AcquireImage(successCallback, failureCallback);
function successCallback() {
  console.log("successful");
}
function failureCallback(errorCode, errorString) {
  alert(errorString);
}

GetCurrentDocumentName()

Get the current document name. The default value is ‘dynamsoft-default-document’. Scanned image(s) are saved in this document by default if no document name is created.

Syntax

GetCurrentDocumentName():string;

Availability

RenameDocument()

Rename a document.

Syntax

RenameDocument(oldDocumentName:string, newDocumentName:string):boolean;

Parameters

oldDocumentName: Specify the old document name.

newDocumentName: Specify the new document name.

Availability

RemoveDocument()

Delete the specified document.

Syntax

RemoveDocument(documentName:string):boolean;

Parameters

documentName: Specify the document name.

Availability

GetDocumentInfoList()

Get the list of all documents and their information.

Syntax

GetDocumentInfoList(): DocumentInfo[];

Arguments

DocumentInfo: Please refer to DocumentInfo.

Availability

updateImage()

Update the specified image with a new image.

Syntax

updateImage(imageId: string, blob: Blob): Promise <void>;

Parameters

imageId: Specify the image to be updated by its image id.

blob: The blob of the new image. Only support the blob which contains single image page. Multi-pages Tiff and PDF are not supported.

Availability

Usage notes

Supported blob type: image/jpeg, image/png, image/bmp, image/tiff, application/pdf, image/jpg, image/tif.

OnDiskExceedLimit

A built-in callback triggered when disk cache exceeds the limit.

Syntax

RegisterEvent('OnDiskExceedLimit',
    function () {}
): boolean;

Availability

Usage notes