Telegram Bot Java API: Poor Quality Downloaded Images

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1

Using the Telegram Java API, images received are lower in quality. The handling within the code might be degrading resolution. Below is an alternative sample:

List<ImageData> imgs = update.getImages();
for (ImageData img : imgs) {
    FileQuery query = new FileQuery(img.getUniqueId());
    FileMeta meta = fetchFileMeta(query);
    String fullUrl = BASE_URL + meta.getPath();
    File localFile = retrieveFile(fullUrl);
    byte[] imgContent = java.nio.file.Files.readAllBytes(localFile.toPath());
    dbHandler.storeImage(imgContent);
}

private File retrieveFile(String urlStr) throws Exception {
    URL url = new URL(urlStr);
    InputStream stream = url.openStream();
    File tempFile = new File(System.getProperty("user.home"), "temp_" + System.currentTimeMillis() + ".jpg");
    java.nio.file.Files.copy(stream, tempFile.toPath(), java.nio.file.StandardCopyOption.REPLACE_EXISTING);
    return tempFile;
}

byte[] imageData = dbHandler.getImage();
File outFile = new File("temp_send.jpg");
java.nio.file.Files.write(outFile.toPath(), imageData);
sendPhoto(update.getChatId(), outFile);
outFile.delete();
2

I have encountered a similar issue with the Telegram API before and found that sometimes the problem wasn’t with the API itself but with how the downloaded file was processed afterward. In my experience, the key device was ensuring that the file reading and writing processes did not inadvertently trigger any compression or subsampling. I had to check that I was not using any intermediary image conversion libraries that might have adjusted quality. Streamlining the download and saving methods to work purely at the byte level helped me maintain the original image quality.

3

A thorough review of the code revealed that when using the Telegram API, the image quality may suffer if the wrong version of the file is retrieved. I experienced a similar issue by unintentionally downloading a smaller thumbnail version rather than the original high-resolution file. My solution involved verifying that I was requesting the correct file metadata and confirming that the URL built for download pointed to the best available resolution. Reviewing the API documentation closely and checking metadata values resolved the quality drop considerably.