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[英]How to improve the image quality before the image processing start in javacv or opencv?
[英]How to improve quality of signature image embedded in pdf
我正在一个Web应用程序上将签名嵌入到pdf文档中。 我正在使用以下库Zetakey Sign&Send 。从签名板签名使用以下命令捕获:
var dataURL = canvas.toDataURL("image/png",1);
并且在服务器端(首先对签名字符串进行Base64解码):
public String createSignature(String mySignature,int width,int height) throws IOException {
String filePath = SIGNATURE_PATH +"signature_" + new Date().getTime() + ".png";
byte[] imageByteArray = decodeImage(mySignature);
try(FileOutputStream imageOutFile = new FileOutputStream(filePath)){
imageOutFile.write(imageByteArray);
}
try {
BufferedImage image = ImageIO.read(new File(filePath));
image = scaleImage(image, width, height);
ImageIO.write(image, "png", new File(filePath));
for(Iterator<ImageWriter> iw = ImageIO.getImageWritersByFormatName("png"); iw.hasNext();) {
ImageWriter writer = iw.next();
ImageWriteParam writeParam = writer.getDefaultWriteParam();
ImageTypeSpecifier typeSpecifier = ImageTypeSpecifier.createFromBufferedImageType(BufferedImage.TYPE_INT_RGB);
IIOMetadata metadata = writer.getDefaultImageMetadata(typeSpecifier, writeParam);
if(metadata.isReadOnly() || !metadata.isStandardMetadataFormatSupported()) {
continue;
}
setDPI(metadata,500,width,height);
try (ImageOutputStream stream = ImageIO.createImageOutputStream(new FileOutputStream(filePath))){
writer.setOutput(stream);
writer.write(metadata, new IIOImage(image, null, metadata), writeParam);
}
break;
}
} catch (IOException e) {
logger.error(e.getMessage());
}
return filePath;
}
private static void setDPI(IIOMetadata metadata, int value, int width, int height) throws IIOInvalidTreeException {
double dotsPerMilli = value/(INCH_TO_CM*10);
IIOMetadataNode horiz = new IIOMetadataNode("HorizontalPixelSize");
horiz.setAttribute(VAL, Double.toString(dotsPerMilli));
IIOMetadataNode vert = new IIOMetadataNode("VerticalPixelSize");
vert.setAttribute(VAL, Double.toString(dotsPerMilli));
IIOMetadataNode horizScreenSize = new IIOMetadataNode("HorizontalScreenSize");
horizScreenSize.setAttribute(VAL, Integer.toString(width));
IIOMetadataNode vertScreenSize = new IIOMetadataNode("VerticalScreenSize");
vertScreenSize.setAttribute(VAL, Integer.toString(height));
IIOMetadataNode dim = new IIOMetadataNode("Dimension");
dim.appendChild(horiz);
dim.appendChild(vert);
dim.appendChild(horizScreenSize);
dim.appendChild(vertScreenSize);
IIOMetadataNode root = new IIOMetadataNode("javax_imageio_1.0");
root.appendChild(dim);
metadata.mergeTree("javax_imageio_1.0", root);
}
public static BufferedImage scaleImage(BufferedImage original, int width, int height){
BufferedImage scaled = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
AffineTransform at = new AffineTransform();
at.scale(((float)width)/original.getWidth(), ((float)height)/original.getHeight());
Map<RenderingHints.Key, Object> map = new HashMap<>();
map.put(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
map.put(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
map.put(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
RenderingHints hints = new RenderingHints(map);
AffineTransformOp scaleOp = new AffineTransformOp(at, hints);
scaled = scaleOp.filter(original, scaled);
return scaled;
}
但是,即使尝试500 DPI,打印在pdf上的签名图像的质量也完全不能令人满意。我错过了什么吗?
因此,使用ZetaKey的现场演示,签名捕获返回了可接受的高质量PNG图像...
请考虑以下事项:
我怀疑您正在失去图像分辨率,因为缩放图像后正在调整DPI。
缩放和DPI的影响:
摘录:(不直接相关,但可以深入了解问题)
现在,假设您要使用普通胶印机打印图像,该胶印机最多可以打印300dpi图像。 假设您尝试以英寸为单位的原始图像尺寸进行精确打印。 印刷机每英寸需要300个点才能做好。 您提供的图像每英寸只有72个点,因此印刷机(或更准确地说,是为印刷机准备印版的软件)必须弥补缺失的点。 结果将是模糊的或嘈杂的,因为该软件将创造性地添加很多“过渡”点来填补缺失的空白。
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