GD imagejpeg（）压缩？ [英] GD imagejpeg() compression?

问题描述

我正在一个项目中，我编辑的jpg的PHP使用GD库的像素。
它的非常关键，并且我的项目的关键，PHP输出保留像素值我设置（cough-steganography-cough）。

I'm working on a project where I edit the pixels of a jpg in PHP using the GD library. Its very crucial and key to my project that the output from PHP retains the pixel values I set (cough-steganography-cough).

这是我第一次尝试在PHP中进行图像处理。我之前在我的Java实现没有问题，所以我很愚蠢的不调查GD的 jpeg 压缩质量，然后继续。

This is the first time I've attempted image manipulation in PHP. I've had no problems before in my Java implementations, so I was foolish not to investigate GD's jpeg compression quality before pursuing further.

事实证明，经过我所有的努力，我的代码不会按照它的方式运行。我很确定它不是我的代码（测试编辑和图像资源的编码和解码功能，他们工作）。

It turns out that after all my effort, my code does not function the way its supposed to. I am pretty sure it is not my code (tested the encode and decode functions on edited image resources and they worked).

我的问题是：

1. 我可以看到的唯一问题是 imagejpeg（）压缩。

是否有任何库提供我需要的压缩？（保留我更改的像素值）

Are there any libraries that provide the compression that I need?(retain pixel values that I changed)

推荐答案

如果您使用JPEG格式，那么 JPEG 隐身图片逐像素。

The JPEG file format is not very suitable for steganography if you do the steganography pixel by pixel.

JPEG 使用图像压缩 - 即使具有最高质量，也会破坏每个像素的位级别的信息。 jpeg压缩类型（ 有损压缩 ）是为人类眼睛/大脑保留图像，但不保留文件中图像的位。

JPEG uses an image compression - that even with maximum quality - that will destroy the information on the bit level on each pixel. The jpeg type of compression (lossy compression) is made for the human eye/brain to retain the image but not the bits of the image in the file .

您需要使用能够保留像素的图像格式写了它已经一样好。这种格式更有可能是具有 RLE 压缩的 BMP 或具有 ZIP 或 RLE的 TIFF 压缩。这称为 无损数据压缩 。

You need to use an image format that is capable to retain the pixels - as you wrote it already as well. Such a format more likely is BMP with RLE compression or the TIFF image format with ZIP or RLE compression. That's called lossless data compression.

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