---
layout: default-layout
needAutoGenerateSidebar: true
title: Dynamic Web TWAIN SDK API Reference - Buffer APIs
keywords: Dynamic Web TWAIN, Documentation, API Reference, Buffer APIs
breadcrumbText: Buffer
description: Dynamic Web TWAIN SDK Documentation API Reference Buffer APIs Page
---
# {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](/_articles/extended-usage/advanced-initialization.md#instantiating-webtwain-without-onwebtwainready).
**Methods**
| [`ClearImageTags()`](#clearimagetags) | [`RenameTag()`](#renametag) | [`RemoveTag()`](#removetag) | [`GetTagList()`](#gettaglist) |
| [`FilterImagesByTag()`](#filterimagesbytag) | [`ClearFilter()`](#clearfilter) | [`SetDefaultTag()`](#setdefaulttag) | [`TagImages()`](#tagimages) |
| [`GetImageBitDepth()`](#getimagebitdepth) | [`GetImageSize()`](#getimagesize) | [`GetImageSizeWithSpecifiedType()`](#getimagesizewithspecifiedtype) | [`GetSelectedImagesSize()`](#getselectedimagessize) |
| [`GetImageHeight()`](#getimageheight) | [`GetImageWidth()`](#getimagewidth) | [`GetImagePartURL()`](#getimageparturl) | [`GetImageURL()`](#getimageurl) |
| [`GetImageXResolution()`](#getimagexresolution) | [`GetImageYResolution()`](#getimageyresolution) | [`GetSkewAngle()`](#getskewangle) | [`GetSkewAngleEx()`](#getskewangleex) |
| [`ImageIDToIndex()`](#imageidtoindex) | [`IndexToImageID()`](#indextoimageid) | [`IsBlankImage()`](#isblankimage) | [`IsBlankImageExpress()`](#isblankimageexpress) |
| [`SelectAllImages()`](#selectallimages) | [`MoveImage()`](#moveimage) | [`SwitchImage()`](#switchimage) | [`RemoveImage()`](#removeimage) |
| [`IsBlankImageAsync()`](#isblankimageasync) | [`RemoveAllImages()`](#removeallimages) | [`RemoveAllSelectedImages()`](#removeallselectedimages) | [`SelectImages()`](#selectimages) |
| [`GetTagListByIndex()`](#gettaglistbyindex) | [`CreateDocument()`](#createdocument) | [`OpenDocument()`](#opendocument) | [`GetCurrentDocumentName()`](#getcurrentdocumentname) |
| [`RenameDocument()`](#renamedocument) | [`RemoveDocument()`](#removedocument) | [`GetDocumentInfoList()`](#getdocumentinfolist) | [`CopyToDocumentAsync()`](#copytodocumentasync) |
| [`MoveToDocumentAsync()`](#movetodocumentasync) | [`updateImage()`](#updateimage) | | |
**Properties**
| [`BlankImageCurrentStdDev`](#blankimagecurrentstddev) | [`BlankImageMaxStdDev`](#blankimagemaxstddev) | [`BlankImageThreshold`](#blankimagethreshold) | [`BufferMemoryLimit`](#buffermemorylimit) |
| [`CurrentImageIndexInBuffer`](#currentimageindexinbuffer) | [`HowManyImagesInBuffer`](#howmanyimagesinbuffer) | [`IfAllowLocalCache`](#ifallowlocalcache) | [`SelectedImagesIndices`](#selectedimagesindices) |
| [`MaxImagesInBuffer`](#maximagesinbuffer) | | | |
**Events**
| [`OnBufferChanged`](#onbufferchanged) | [`OnBitmapChanged`](#onbitmapchanged) | [`OnIndexChangeDragDropDone`](#onindexchangedragdropdone) |
| [`OnTopImageInTheViewChanged`](#ontopimageintheviewchanged) | [`OnDiskExceedLimit`](#ondiskexceedlimit) | |
---
## IndexToImageID()
Return the imageId of an image specified by the index.
**Syntax**
```typescript
IndexToImageID(index: number): string;
```
**Parameters**
`index`: The index of the image.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v15.0+ |
v15.0+ |
v15.0+ |
v15.0+ |
---
## ImageIDToIndex()
Return the index of an image specified by the imageId.
**Syntax**
```typescript
ImageIDToIndex(imageId: string): number;
```
**Parameters**
`imageId`: The imageId of the image.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v15.0+ |
v15.0+ |
v15.0+ |
v15.0+ |
**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**
```typescript
RenameTag(oldTag:string, newTag:string): boolean;
```
**Parameters**
`oldTag`: Specify the tag to change.
`newTag`: Specify the new tag name.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v16.2+ |
v16.2+ |
v16.2+ |
v16.2+ |
---
## RemoveTag()
Remove the specified tag from one or more images(if not specified, remove from all).
**Syntax**
```typescript
RemoveTag(tagName: string, indices?: number[]):boolean
```
**Parameters**
`tagName`: Specify the tag to be removed.
`indices`: Specify the index.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v17.0+ |
v17.0+ |
v17.0+ |
v17.0+ |
**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**
```typescript
GetTagList(): TagInfo[];
```
**Arguments**
`TagInfo`: Please refer to [TagInfo](/_articles/info/api/interfaces.md#taginfo).
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v17.0+ |
v17.0+ |
v17.0+ |
v17.0+ |
---
## ClearImageTags()
Remove all tags from the specified image.
**Syntax**
```typescript
ClearImageTags(index: number): boolean;
```
**Parameters**
`index`: Specify the image.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v15.2+ |
v15.2+ |
v15.2+ |
v15.2+ |
---
## FilterImagesByTag()
Filter images by the specified tag.
**Syntax**
```typescript
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**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v15.2+ |
v15.2+ |
v15.2+ |
v15.2+ |
---
## ClearFilter()
Stop filtering images by tag.
**Syntax**
```typescript
ClearFilter(): boolean;
```
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v16.2+ |
v16.2+ |
v16.2+ |
v16.2+ |
---
## SetDefaultTag()
Set a default tag for newly incoming images.
**Syntax**
```typescript
SetDefaultTag(tag: string): boolean;
```
**Parameters**
`tag`: Specifies the tag.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v15.2+ |
v15.2+ |
v15.2+ |
v15.2+ |
---
## TagImages()
Add a tag to specified images.
**Syntax**
```typescript
TagImages(indices: number[], tag: string): boolean;
```
**Parameters**
`indices`: Specifies images to be tagged.
`tag`: Specify the tag.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v15.2+ |
v15.2+ |
v15.2+ |
v15.2+ |
---
## GetImageBitDepth()
Return the pixel bit depth of the specified image.
**Syntax**
```typescript
GetImageBitDepth(index: number): number;
```
**Parameters**
`index`: Specify the image.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v6.2+ |
v6.2+ |
v6.2+ |
v6.2+ |
---
## GetImageHeight()
Return the height (in pixels) of the specified image.
**Syntax**
```typescript
GetImageHeight(index: number): number;
```
**Parameters**
`index`: Specify the image.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v6.2+ |
v6.2+ |
v6.2+ |
v6.2+ |
---
## GetImageWidth()
Return the width (in pixels) of the specified image.
**Syntax**
```typescript
GetImageWidth(index: number): number;
```
**Parameters**
`index`: Specify the image.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v6.2+ |
v6.2+ |
v6.2+ |
v6.2+ |
---
## GetImageXResolution()
Return the horizontal resolution of the specified image.
**Syntax**
```typescript
GetImageXResolution(index: number): number;
```
**Parameters**
`index`: Specify the image.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v8.0+ |
v8.0+ |
v8.0+ |
v8.0+ |
---
## GetImageYResolution()
Return the vertical resolution of the specified image.
**Syntax**
```typescript
GetImageYResolution(index: number): number;
```
**Parameters**
`index`: Specify the image.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v8.0+ |
v8.0+ |
v8.0+ |
v8.0+ |
---
## GetSkewAngle()
Return the skew angle of the specified image.
**Syntax**
```typescript
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**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v9.0+ |
v9.0+ |
v9.0+ |
v9.0+ |
---
## GetSkewAngleEx()
Return the skew angle of the specified rectangle on the specified image.
**Syntax**
```typescript
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**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v9.0+ |
v9.0+ |
v9.0+ |
v9.0+ |
**Usage notes**
After you get the skew angle of an image, you can rotate it with the method [`Rotate()`](/_articles/info/api/WebTwain_Edit.md#rotate) to perform de-skewing.
---
## GetImageSize()
Calculate the size in bytes of the specified image assuming it's resized to the given dimensions.
**Syntax**
```typescript
GetImageSize(index: number, width: number, height: number): number;
```
**Parameters**
`index`: Specify the image.
`width`: Specify the width.
`height`: Specify the height.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| all versions |
all versions |
all versions |
all versions |
---
## GetImageSizeWithSpecifiedType()
Calculate the size in bytes of the specified image assuming an expected file type.
**Syntax**
```typescript
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`](/_articles/info/api/Dynamsoft_Enum.md#dynamsoftdwtenumdwt_imagetype).
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| all versions |
all versions |
all versions |
all versions |
---
## GetSelectedImagesSize()
Calculate the size in bytes of all selected images assuming an expected file type.
**Syntax**
```typescript
GetSelectedImagesSize(type: Dynamsoft.DWT.EnumDWT_ImageType | number): number;
```
**Parameters**
`type`: Specify the expected file type. Please refer to [`Dynamsoft.DWT.EnumDWT_ImageType`](/_articles/info/api/Dynamsoft_Enum.md#dynamsoftdwtenumdwt_imagetype).
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v6.0+ |
v6.0+ |
v6.0+ |
v6.0+ |
**Usage notes**
If the calculation fails, -1 is returned.
---
## GetImagePartURL()
Return the internal URL of the specified image.
**Syntax**
```typescript
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**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v13.0+ |
v13.0+ |
v13.0+ |
v13.0+ |
**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
- 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**
```typescript
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**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v12.0+ |
v12.0+ |
v12.0+ |
v12.1+ |
**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
- 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**
```typescript
SelectAllImages(): number[];
```
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v15.3+ |
v15.3+ |
v15.3+ |
v15.3+ |
---
## SelectImages()
Select the specified images.
**Syntax**
```typescript
SelectImages(indices: number[]): boolean;
```
**Parameters**
`indices`: Specify one or multiple images
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v16.0+ |
v16.0+ |
v16.0+ |
v16.0+ |
---
## MoveImage()
Change the position of an image in the buffer.
**Syntax**
```typescript
MoveImage(from: number, to: number): boolean;
```
**Parameters**
`from`: Specify the original position by index.
`to`: Specify the target position by index.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v10.0+ |
v11.0+ |
v11.0+ |
v12.1+ |
---
## SwitchImage()
Exchange the positions of two images.
**Syntax**
```typescript
SwitchImage(index1: number, index2: number): boolean;
```
**Parameters**
`index1`: Specify the 1st image.
`index2`: Specify the 2nd image.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v10.0+ |
v11.0+ |
v11.0+ |
v12.1+ |
---
## RemoveImage()
Remove the specified image.
**Syntax**
```typescript
RemoveImage(index: number): boolean;
```
**Parameters**
`index`: Specify the image.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v10.0+ |
v11.0+ |
v11.0+ |
v12.1+ |
---
## RemoveAllImages()
Remove all images.
**Syntax**
```typescript
RemoveAllImages(): boolean;
```
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v10.0+ |
v11.0+ |
v11.0+ |
v12.1+ |
---
## RemoveAllSelectedImages()
Remove all selected images.
**Syntax**
```typescript
RemoveAllSelectedImages(): boolean;
```
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v10.0+ |
v11.0+ |
v11.0+ |
v12.1+ |
---
## CurrentImageIndexInBuffer
Return the index of the current image in the buffer or set the image specified by index as the current image.
**Syntax**
```typescript
CurrentImageIndexInBuffer: number;
```
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v4.0+ |
v4.0+ |
v4.0+ |
v4.0+ |
---
## HowManyImagesInBuffer
Return how many images are held in the buffer
**Syntax**
```typescript
readonly HowManyImagesInBuffer: number;
```
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v4.0+ |
v4.0+ |
v4.0+ |
v4.0+ |
---
## MaxImagesInBuffer
Return or set how many images can be held in the buffer.
**Syntax**
```typescript
MaxImagesInBuffer: number;
```
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v4.0+ |
v4.0+ |
v4.0+ |
v4.0+ |
**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**
```typescript
readonly SelectedImagesIndices: number[];
```
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v16.0+ |
v16.0+ |
v16.0+ |
v16.0+ |
---
## SelectionRectAspectRatio
Specify a aspect ratio to be used when selecting a rectangle on an image.
**Syntax**
```typescript
SelectionRectAspectRatio: number;
```
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v10.0+ |
v11.0+ |
v11.0+ |
v12.1+ |
---
## BlankImageCurrentStdDev
Return the deviation of the pixels of the image on which black image detection was last called. This property is only valid after calling [`IsBlankImageExpress()`](/_articles/info/api/WebTwain_Buffer.md#isblankimageexpress) or [`IsBlankImage()`](/_articles/info/api/WebTwain_Buffer.md#isblankimage). `BlankImageCurrentStdDev` **does not apply to [`IsBlankImageAsync()`](/_articles/info/api/WebTwain_Buffer.md#isblankimageasync)** - it uses its own detection parameters.
**Syntax**
```typescript
readonly BlankImageCurrentStdDev: number;
```
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v8.0+ |
v8.0+ |
v8.0+ |
v8.0+ |
---
## BlankImageMaxStdDev
Return or set the maximum deviation of the pixels in an image which is used to determine whether the image is blank. The value of this property applies on subsequent calls of [`IsBlankImageExpress()`](/_articles/info/api/WebTwain_Buffer.md#isblankimageexpress) or [`IsBlankImage()`](/_articles/info/api/WebTwain_Buffer.md#isblankimage). `BlankImageCurrentStdDev` **does not apply to [`IsBlankImageAsync()`](/_articles/info/api/WebTwain_Buffer.md#isblankimageasync)** - it uses its own detection parameters.
**Syntax**
```typescript
BlankImageMaxStdDev: number;
```
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v5.2+ |
v5.2+ |
v5.2+ |
v5.2+ |
**Usage notes**
[0, 100] is the interval of allowed values, inclusive. For example, a value of 0 detects markings on any image with more than one color. The default value is 1.
---
## BlankImageThreshold
Return or set the dividing line between black and white for subsequent calls to [`IsBlankImageExpress()`](/_articles/info/api/WebTwain_Buffer.md#isblankimageexpress) or [`IsBlankImage()`](/_articles/info/api/WebTwain_Buffer.md#isblankimage). `BlankImageCurrentStdDev` **does not apply to [`IsBlankImageAsync()`](/_articles/info/api/WebTwain_Buffer.md#isblankimageasync)** - it uses its own detection parameters.
**Syntax**
```typescript
BlankImageThreshold: number;
```
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v5.2+ |
v5.2+ |
v5.2+ |
v5.2+ |
**Usage notes**
[0, 255] is the interval of allowed values, inclusive. The default value is 128.
---
## 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**
```typescript
BufferMemoryLimit: number;
```
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v10.1+ |
v10.1+ |
v11.0+ |
v12.1+ |
**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 based on the standard deviation in pixels.
**Syntax**
```typescript
IsBlankImage(index: number): boolean;
```
**Parameters**
`index`: Specify the image.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v5.2+ |
v5.2+ |
v5.2+ |
v5.2+ |
---
**Usage Notes**
See also:
- [`BlankImageCurrentStdDev()`](/_articles/info/api/WebTwain_Buffer.md#blankimagecurrentstddev)
- [`BlankImageMaxStdDev()`](/_articles/info/api/WebTwain_Buffer.md#blankimagemaxstddev)
- [`BlankImageThreshold()`](/_articles/info/api/WebTwain_Buffer.md#blankimagethreshold)
## IsBlankImageAsync()
Check whether the specified image is blank. This API employs a different algorithm than the one used in [`IsBlankImage()`](/_articles/info/api/WebTwain_Buffer.md#isblankimage) and [`IsBlankImageExpress()`](/_articles/info/api/WebTwain_Buffer.md#isblankimageexpress) and is the recommended blank image detection method.
You can set `minBlockHeight` and `maxBlockHeight` to the expected text pixel height. In most cases, these values do not require adjustment.
> [!NOTE]
> `IsBlankImageAsync()` **is not** related to [`BlankImageCurrentStdDev()`](/_articles/info/api/WebTwain_Buffer.md#blankimagecurrentstddev), [`BlankImageMaxStdDev()`](/_articles/info/api/WebTwain_Buffer.md#blankimagemaxstddev), or [`BlankImageThreshold()`](/_articles/info/api/WebTwain_Buffer.md#blankimagethreshold).
**Syntax**
```typescript
IsBlankImageAsync(index: number,
options?: {
minBlockHeight?: number,
maxBlockHeight?: number,
}
): Promise ;
```
**Parameters**
`index`: Specify the image in buffer to be analyzed.
`minBlockHeight`: Minimum height of the blocks to be detected. Default value: 20.
`maxBlockHeight`: Maximum height of the blocks to be detected. Default value: 30.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v18.4+ |
v19.2+ |
v19.2+ |
v19.2+ |
---
## IsBlankImageExpress()
Check whether the specified image is blank based on the standard deviation in pixels.
**Syntax**
```typescript
IsBlankImageExpress(index: number): boolean;
```
**Parameters**
`index`: Specify the image.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v10.0+ |
v10.0+ |
v10.0+ |
v10.0+ |
**Usage notes**
[`IsBlankImage()`](/_articles/info/api/WebTwain_Buffer.md#isblankimage) is more accurate than [`IsBlankImageExpress()`](/_articles/info/api/WebTwain_Buffer.md#isblankimageexpress) but it works slower.
[`BlankImageCurrentStdDev`](/_articles/info/api/WebTwain_Buffer.md#blankimagecurrentstddev) should be read after either [`IsBlankImage()`](/_articles/info/api/WebTwain_Buffer.md#isblankimage) or [`IsBlankImageExpress()`](/_articles/info/api/WebTwain_Buffer.md#isblankimageexpress).
If you believe an image should be blank but [`IsBlankImage()`](/_articles/info/api/WebTwain_Buffer.md#isblankimage) or [`IsBlankImageExpress()`](/_articles/info/api/WebTwain_Buffer.md#isblankimageexpress) is returning `false`, you can read [`BlankImageCurrentStdDev`](/_articles/info/api/WebTwain_Buffer.md#blankimagecurrentstddev) for that image and then set a bigger value to [`BlankImageMaxStdDev`](/_articles/info/api/WebTwain_Buffer.md#blankimagemaxstddev).
Both [`BlankImageCurrentStdDev`](/_articles/info/api/WebTwain_Buffer.md#blankimagecurrentstddev) and [`BlankImageMaxStdDev`](/_articles/info/api/WebTwain_Buffer.md#blankimagemaxstddev) range from 0 to 100.
If the image is not blank and it is not black and white, [`IsBlankImage()`](/_articles/info/api/WebTwain_Buffer.md#isblankimage) or [`IsBlankImageExpress()`](/_articles/info/api/WebTwain_Buffer.md#isblankimageexpress) may return `true`. In that case, you can increase the [`BlankImageThreshold`](/_articles/info/api/WebTwain_Buffer.md#blankimagethreshold) value so that the image is not detected as blank.
---
## IfAllowLocalCache
Return or set whether the feature of disk caching is enabled.
**Syntax**
```typescript
IfAllowLocalCache: boolean;
```
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v10.0+ |
v10.0+ |
v11.0+ |
v12.1+ |
**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`](/_articles/info/api/WebTwain_Buffer.md#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**
```typescript
RegisterEvent('OnBufferChanged',
function (bufferChangeInfo: BufferChangeInfo) {}
): boolean;
```
**Parameters**
`bufferChangeInfo`: Details about the buffer change. Please refer to [`BufferChangeInfo`](/_articles/info/api/interfaces.md#bufferchangeinfo).
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v16.2+ |
v16.2+ |
v16.2+ |
v16.2+ |
**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**
```typescript
RegisterEvent('OnBitmapChanged',
function (
indices: number[],
type: number,
index: number
) {}
): boolean;
```
**Parameters**
`indices`: Array of the changed index(indices).
`type`: Operation type:
- `1`: new image(s) added at the tail
- `2`: image(s) inserted before the current index
- `3`: image(s) deleted
- `4`: image(s) modified
`index`: Index of the current image.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v10.0+ |
v10.0+ |
v11.0+ |
v12.1+ |
**Example**
```javascript
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**
```typescript
RegisterEvent('OnTopImageInTheViewChanged',
function (index: number) {}
): boolean;
```
**Parameters**
`index`: Index of the current image.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v10.1+ |
v11.0+ |
v11.0+ |
v12.1+ |
**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**
```typescript
RegisterEvent('OnIndexChangeDragDropDone',
function (indexPairs: Pair[]) {}
): boolean;
Pair: [from: number, to: number];
```
**Parameters**
`indexPairs`: The list of index changes.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v15.0+ |
v15.0+ |
v15.0+ |
v15.0+ |
---
## GetTagListByIndex()
Return the tag(s) of a specified image.
**Syntax**
```typescript
GetTagListByIndex(index: number):string[]
```
**Parameters**
`index`: Index of the image.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v17.2+ |
v17.2+ |
v17.2+ |
v17.2+ |
**Example**
```javascript
DWTObject.GetTagListByIndex(0);
```
---
## CopyToDocumentAsync()
Copy specified images to another document.
**Syntax**
```typescript
CopyToDocumentAsync(from: string, to: string): Promise;
CopyToDocumentAsync(from: string, to: string, sourceIndices: number[]): Promise;
CopyToDocumentAsync(from: string, to: string, targetIndex: number): Promise;
CopyToDocumentAsync(from: string, to: string, sourceIndices: number[], targetIndex: number): Promise;
```
**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**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v18.4+ |
v18.4+ |
v18.4+ |
v18.4+ |
**Example**
```typescript
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**
```typescript
CreateDocument(documentName:string):boolean;
```
**Parameters**
`documentName`: Specify the document name.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v17.2+ |
v17.2+ |
v17.2+ |
v17.2+ |
**Example**
```javascript
//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**
```typescript
MoveToDocumentAsync(from: string, to: string): Promise;
MoveToDocumentAsync(from: string, to: string, sourceIndices: number[]): Promise;
MoveToDocumentAsync(from: string, to: string, targetIndex: number): Promise;
MoveToDocumentAsync(from: string, to: string, sourceIndices: number[], targetIndex: number): Promise;
```
**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**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v18.4+ |
v18.4+ |
v18.4+ |
v18.4+ |
**Example**
```typescript
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**
```typescript
OpenDocument(documentName:string):boolean;
```
**Parameters**
`documentName`: Specify the document name.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v17.2+ |
v17.2+ |
v17.2+ |
v17.2+ |
**Example**
```javascript
//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**
```typescript
GetCurrentDocumentName():string;
```
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v17.2+ |
v17.2+ |
v17.2+ |
v17.2+ |
---
## RenameDocument()
Rename a document.
**Syntax**
```typescript
RenameDocument(oldDocumentName:string, newDocumentName:string):boolean;
```
**Parameters**
`oldDocumentName`: Specify the old document name.
`newDocumentName`: Specify the new document name.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v17.3+ |
v17.3+ |
v17.3+ |
v17.3+ |
---
## RemoveDocument()
Delete the specified document.
**Syntax**
```typescript
RemoveDocument(documentName:string):boolean;
```
**Parameters**
`documentName`: Specify the document name.
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v17.2+ |
v17.2+ |
v17.2+ |
v17.2+ |
---
## GetDocumentInfoList()
Get the list of all documents and their information.
**Syntax**
```typescript
GetDocumentInfoList(): DocumentInfo[];
```
**Arguments**
`DocumentInfo`: Please refer to [`DocumentInfo`](/_articles/info/api/interfaces.md#documentinfo).
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v17.2+ |
v17.2+ |
v17.2+ |
v17.2+ |
---
## updateImage()
Update the specified image with a new image.
**Syntax**
```typescript
updateImage(imageId: string, blob: Blob): Promise ;
```
**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**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v18.5+ |
v18.5+ |
v18.5+ |
v18.5+ |
**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**
```typescript
RegisterEvent('OnDiskExceedLimit',
function () {}
): boolean;
```
**Availability**
| H5(Windows) |
H5(macOS/TWAIN) |
H5(macOS/ICA) |
H5(Linux) |
| v18.5+ |
v18.5+ |
v18.5+ |
v18.5+ |
**Usage notes**
| System | Triggered when |
| ----------- | -------------- |
| Windows x86 | < 1.2GB |
| Windows x64 | < 4GB |
| macOS 32bit | < 1.2GB |
| macOS 64bit | < 4GB |
| Linux | < 4GB |