harmony 鸿蒙PixelMap Operation

2023-06-24
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PixelMap Operation

To process a certain area in an image, you can perform PixelMap operations, which are usually used to beautify the image.

As shown in the figure below, the pixel data of a rectangle in an image is read, modified, and then written back to the corresponding area of the original image.

Figure 1 PixelMap operation

PixelMap operation

How to Develop

Read Image for APIs related to PixelMap operations.

Complete image decoding and obtain a PixelMap object.
Obtain information from the PixelMap object.

   import image from '@ohos.multimedia.image';
   // Obtain the total number of bytes of this PixelMap object.
   let pixelBytesNumber : number = pixelMap.getPixelBytesNumber();
   // Obtain the number of bytes per row of this PixelMap object.p
   let rowCount : number = pixelMap.getBytesNumberPerRow();
   // Obtain the pixel density of the image. Pixel density refers to the number of pixels per inch of an image. A larger value of the pixel density indicates a finer image.
   let getDensity : number = pixelMap.getDensity();

Read and modify the pixel data of the target area, and write the modified data back to the original image.

   import {BusinessError} from '@ohos.base'
   // Scenario 1: Read the pixel data of the entire image and write the modified data to an array buffer.
   const readBuffer = new ArrayBuffer(pixelBytesNumber);
   pixelMap.readPixelsToBuffer(readBuffer).then(() => {
     console.info('Succeeded in reading image pixel data.');
   }).catch((error : BusinessError) => {
     console.error('Failed to read image pixel data. And the error is: ' + error);
   })
   
   // Scenario 2: Read the pixel data in a specified area and write the modified data to area.pixels.
   const area : image.PositionArea = {
     pixels: new ArrayBuffer(8),
     offset: 0,
     stride: 8,
     region: { size: { height: 1, width: 2 }, x: 0, y: 0 }
   }
   pixelMap.readPixels(area).then(() => {
     console.info('Succeeded in reading the image data in the area.');
   }).catch((error : BusinessError) => {
     console.error('Failed to read the image data in the area. And the error is: ' + error);
   })
   
   // The read image data can be used independently (by creating a PixelMap object) or modified as required.
   // Write area.pixels to the specified area.
   pixelMap.writePixels(area).then(() => {
     console.info('Succeeded to write pixelMap into the specified area.');
   })
   
   // Write the image data result to the PixelMap object.
   const writeColor = new ArrayBuffer(96);
   pixelMap.writeBufferToPixels(writeColor, () => {});