如何在Android上创建渐进式JPEG图像 [英] How to create a progressive JPEG image on Android

问题描述

我需要通过非常低带宽连接从Android手机(低至10kByte/s)发送图像，并希望以逐行(隔行)模式发送图像，以便在漫长的传输过程中，另一端已经开始看到图像.现在，我正在使用常规的照片应用程序来创建图像:

I need to send images over a very low-bandwidth connection from an android phone (down to 10kByte/s) and would like to send them in progressive (interlaced) mode so that the user at the other end starts seeing the image already during the lengthy transfer. Right now, I am creating the image with the regular photo app:

Intent takePictureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);

但这会生成非渐进式照片，但我无法发现如何说服它去做其他事情.我探索的第二个选项(读取并重新压缩所拍摄的图像)被挫败了，因为据我所知，Bitmap的compress方法除了格式名称和压缩系数外，不允许任何编码参数:

But this creates non-progressive photos and I have not been able to discover how to convince it to do otherwise. The second option I explored (reading and re-compressing the taken image) got foiled because the Bitmap's compress method does not allow any encoding parameters besides format name and compression factor as far as I could determine:

bitmap.compress(Bitmap.CompressFormat.JPEG, 80, out);

我首选的解决方案是指示照片应用以渐进模式保存.

My preferred solution would be to instruct the photo app to save in progressive mode.

下一个最佳选择是一种Java算法，该算法可以无损地将存储的jpeg转换为渐进式(jpegtran在Linux上做到了，但它在C语言中并且依赖libjepeg).

The next best option would be a Java algorithm that losslessly converts the stored jpeg to progressive (jpegtran does this on Linux, but it is in C and relies on libjepeg).

下一个最好的方法是为android指定相关编码参数的方法，以允许我重新压缩它，或者是一个替代的Java库，执行相同的操作.

The next best would a method to specify the relevant encoding parameters to android allowing me to re-compress it, or an alternative Java library that does the same.

进一步的研究表明，~/android-sdk-linux/source-tree/external/jpeg中的算法已经存在(/system/lib/libjpeg.so)了，但是似乎尚不存在JNI包装器.

Further research revealed that the algorithms are already there (/system/lib/libjpeg.so) with the sources in ~/android-sdk-linux/source-tree/external/jpeg -- but there do not seem to be JNI wrappers readily available.

推荐答案

您看过此文档吗?

http://docs. oracle.com/javase/6/docs/api/javax/imageio/plugins/jpeg/JPEGImageWriteParam.html

似乎有逐行书写支持.

或者，您可以使用例如通过JNI OpenJPEG .参见 http://www.linux-mag.com/id/7697/开始.

Alternatively, you could use e.g. OpenJPEG through JNI. See http://www.linux-mag.com/id/7697/ as a start.

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