如何获得高质量的缩略图 [英] How to get a good quality thumbnail

问题描述

我正在尝试使用Java和我发现JPEG的质量保存为75完全不足以创建一个好看的缩略图。 PNG对我来说也不好看。

这是原始文件的标识输出和两个缩略图：

  $ identify 42486_1.jpg 42486_s1.jpg 42486_s1.png 
 42486_1.jpg JPEG 580x435 580x435 + 0 + 0 8-bit DirectClass 50.6KB 0.000u 0： 00.000 
 42486_s1.jpg [1] JPEG 77x58 77x58 + 0 + 0 8位DirectClass 2.22KB 0.000u 0：00.000 
 42486_s1.png [2] PNG 77x58 77x58 + 0 + 0 8位DirectClass 12.2KB 0.000u 0：00.000 
  

问题

• 如何提高生成的缩略图的质量？


• 如何保存质量更高的JPEG？我想尝试更高的质量并比较结果。我在JavaDoc for ImageIO.write中找不到任何东西。


• 为什么我告诉Scalr我的最大尺寸是77x57并输出图像77x58？我认为这是保持比例，但那是我的最大宽度和最大高度。宽度或高度可以更小但不能更多。

更新：通过网络搜索我找到了一篇文章关于如何。

  private void scaleAndSaveImageWithScalr（String sourceFile，String destFile，int width，int height）
 throws IOException {
 BufferedImage sourceImage = ImageIO.read（new File（sourceFile））; 
 BufferedImage destImage = Scalr.resize（sourceImage，Scalr.Method.QUALITY，width，height）; 
 writeJpeg（destImage，destFile，JPEG_QUALITY）; 
} 
 
 private void scaleAndSaveImageWithJImage（String sourceFile，String destFile，int width，int height）
 throws IOException {
 BufferedImage sourceImage = ImageIO.read（new File（源文件））; 
 ResampleOp resampleOp = new ResampleOp（width，height）; 
 resampleOp.setFilter（ResampleFilters.getLanczos3Filter（））; 
 resampleOp.setUnsharpenMask（AdvancedResizeOp.UnsharpenMask.Normal）; 
 BufferedImage destImage = resampleOp.filter（sourceImage，null）; 
 writeJpeg（destImage，destFile，JPEG_QUALITY）; 
} 
  

使用Scalr生成的JPEG质量90：

使用java-image-scaling生成的JPEG质量90：

我没有收到任何进一步的反馈，所以我的个人结论是java-image-scaling提供了卓越的品质，所以这是我选择的图书馆。

解决方案

这不是你问题的完整答案，但是：

关于JPEG质量：

可以使用设置压缩质量ImageWriteParam as 此处描述。他们建议使用 int 值0 | 1，但我相信你应该实际指定一个介于0.0和1.0之间的浮点值。

关于缩放尺寸问题：

来自 Scalr主页：

注意：如果提供的宽度和高度违反图像的
比例（例如尝试将800×600图像调整为150×150
方格）图书馆将首先查看图像的方向
（横向/正方形或纵向）然后
选择主尺寸
（横向或方形使用宽度，纵向使用高度）重新计算
a正确的次要尺寸; 忽略违反比例的用户传入的内容
。

在你的如果主要尺寸的宽度为77，则高度限制为57将被忽略。

I am trying to create a high quality thumbnail of this image, with Java and Scalr 3.2

This is the relevant source code, where THUMB_WIDTH = 77 and THUMB_HEIGHT = 57

BufferedImage srcImg = ImageIO.read(new File(sourceFile)); 
BufferedImage dstImg = Scalr.resize(srcImg, Scalr.Method.QUALITY, 
    THUMB_WIDTH, THUMB_HEIGHT); 
ImageIO.write(dstImg, format, new File(destFile));

If I use format = "png", here is the result:

If I use format = "jpg", here is the result:

With imagemagick identify I've found out that the JPEG is saved with a quality of 75 that is totally insufficient to create a good looking thumbnail. The PNG doesn't look good either to me.

Here is the output of identify of the original file and the two thumbnails:

$ identify 42486_1.jpg 42486_s1.jpg 42486_s1.png 
42486_1.jpg JPEG 580x435 580x435+0+0 8-bit DirectClass 50.6KB 0.000u 0:00.000
42486_s1.jpg[1] JPEG 77x58 77x58+0+0 8-bit DirectClass 2.22KB 0.000u 0:00.000
42486_s1.png[2] PNG 77x58 77x58+0+0 8-bit DirectClass 12.2KB 0.000u 0:00.000

Questions

• How to improve the quality of the generated thumbnail?
• How to save a JPEG with a higher quality? I'd like to try with higher quality and compare the results. I couldn't find anything in the JavaDoc for ImageIO.write.
• Why I tell Scalr that my maximum dimensions are 77x57 and it output an image 77x58? I think that is to maintain the proportion, but those are my maximum width and maximum height. Width or height could be less but not more.

UPDATE: With a web search I found an article about how to adjust JPEG image compression quality. I wrote my own method to save a BufferedImage setting the quality:

/**
 * Write a JPEG file setting the compression quality.
 * 
 * @param image
 *                a BufferedImage to be saved
 * @param destFile
 *                destination file (absolute or relative path)
 * @param quality
 *                a float between 0 and 1, where 1 means uncompressed.
 * @throws IOException
 *                 in case of problems writing the file
 */
private void writeJpeg(BufferedImage image, String destFile, float quality) 
throws IOException {
    ImageWriter writer = null;
    FileImageOutputStream output = null;
    try {
        writer = ImageIO.getImageWritersByFormatName("jpeg").next();
        ImageWriteParam param = writer.getDefaultWriteParam();
        param.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
        param.setCompressionQuality(quality);
        output = new FileImageOutputStream(new File(destFile));
        writer.setOutput(output);
        IIOImage iioImage = new IIOImage(image, null, null);
        writer.write(null, iioImage, param);
    } catch (IOException ex) {
        throw ex;
    } finally {
        if (writer != null) writer.dispose();
        if (output != null) output.close();
    }
}

Here are the results. PNG:

JPEG quality 75:

JPEG quality 90 (the gravatars on stackoverflow are saved as JPEG quality 90):

and the filesize:

thumb90.jpg JPEG 77x58 77x58+0+0 8-bit DirectClass 6.89KB 0.000u 0:00.000

UPDATE 2: test to compare Scalr with java-image-scaling.

private void scaleAndSaveImageWithScalr(String sourceFile, String destFile, int width, int height)
    throws IOException {
    BufferedImage sourceImage = ImageIO.read(new File(sourceFile));
    BufferedImage destImage = Scalr.resize(sourceImage, Scalr.Method.QUALITY, width, height);
    writeJpeg(destImage, destFile, JPEG_QUALITY);
}

private void scaleAndSaveImageWithJImage(String sourceFile, String destFile, int width, int height)
    throws IOException {
    BufferedImage sourceImage = ImageIO.read(new File(sourceFile));
    ResampleOp resampleOp = new ResampleOp(width, height);
    resampleOp.setFilter(ResampleFilters.getLanczos3Filter());
    resampleOp.setUnsharpenMask(AdvancedResizeOp.UnsharpenMask.Normal);
    BufferedImage destImage = resampleOp.filter(sourceImage, null);
    writeJpeg(destImage, destFile, JPEG_QUALITY);
}

JPEG quality 90 generated with Scalr:

JPEG quality 90 generated with java-image-scaling:

I didn't receive any further feedback, so my personal conclusion is that java-image-scaling provides superior quality, and so it's the library that I choose.

解决方案

This is not a complete answer to your question, but:

Regarding JPEG quality:

Compression quality can be set using a ImageWriteParam as described here. They suggest using an int value of 0|1 but I believe that you should actually specify a float value between 0.0 and 1.0.

Regarding your scaling dimension issues:

From the Scalr homepage:

NOTE: If a width and height are provided that violate the image’s proportions (e.g. attempt to resize an 800×600 image to a 150×150 square) the library will first look at the orientation of the image (landscape/square or portrait) and then select the primary dimension (landscape or square uses width, portrait uses height) to recalculate a correct secondary dimension; ignoring what was passed in by the user that was violating the proportions.

In your case the primary dimension will be a width of 77 and thus your height limit of 57 will be ignored.

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