Utility function to get the image of used range in sheet. It first stores the original cell dimensions, resizes them to a fixed width and height, takes an image and then resizes them back to original.

getSheetImage.ts

const CELL_WIDTH = 60;
const CELL_HEIGHT = 20;
export const getSheetImage = async (): Promise<string> => {
  try {
    const image = await Excel.run(async (context) => {
      const sheet = context.workbook.worksheets.getActiveWorksheet();
      const usedRange = sheet.getUsedRange();
      usedRange.load("address,columnCount,rowCount,format/columnWidth,format/rowHeight");
      await context.sync();

      const columnWidths: Excel.Range[] = [];
      const rowHeights: Excel.Range[] = [];

      for (let i = 0; i < usedRange.columnCount; i++) {
        const column = sheet.getRangeByIndexes(0, i, 1, 1);
        column.load("format/columnWidth");
        columnWidths.push(column);
      }

      for (let i = 0; i < usedRange.rowCount; i++) {
        const row = sheet.getRangeByIndexes(i, 0, 1, 1);
        row.load("format/rowHeight");
        rowHeights.push(row);
      }
      await context.sync();

      usedRange.format.columnWidth = CELL_WIDTH;
      usedRange.format.rowHeight = CELL_HEIGHT;
      await context.sync();

      const usedRangeImage = usedRange.getImage();
      await context.sync();

      for (let i = 0; i < usedRange.columnCount; i++) {
        sheet.getRangeByIndexes(0, i, 1, 1).format.columnWidth = columnWidths[i].format.columnWidth;
      }
      for (let i = 0; i < usedRange.rowCount; i++) {
        sheet.getRangeByIndexes(i, 0, 1, 1).format.rowHeight = rowHeights[i].format.rowHeight;
      }

      return usedRangeImage.value;
    });
    return image;
  } catch (error) {
    console.log("ERROR WHILE TAKING RANGE IMAGE", error);
    throw error;
  }
};