GD imagejpeg() 压缩？
我正在开发一个项目，使用 GD 库在 PHP 中编辑 jpg 的像素。 PHP 的输出保留了我设置的像素值（咳嗽-隐写术-咳嗽），这对我的项目来说是非常重要和关键。
这是我第一次尝试用 PHP 进行图像处理。我以前在 Java 实现中没有遇到过任何问题，所以我很愚蠢，没有在进一步研究之前研究 GD 的 jpeg 压缩质量。
事实证明，经过我的努力，我的代码并没有按照预期的方式运行。我很确定这不是我的代码（在编辑的图像资源上测试了编码和解码功能并且它们有效）。
我的问题是：
我看到的唯一问题是
imagejpeg()的压缩。我是对的吗？是否有任何库可以提供我需要的压缩？（保留我更改的像素值）
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).
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.
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).
My questions are:
The only problem I can see is with
imagejpeg()'s compression. Could I be right?Are there any libraries that provide the compression that I need?(retain pixel values that I changed)
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默认情况下，
imagejpeg输出的图像质量为 75，尝试将其设置为 100 以获得完整质量的图像。查看手册了解更多详细信息。
还可以尝试使用 imagecopyresampled。 （我认为您会在代码中的某处使用
imagecopyresized。使用imagecopyresampled而不是它。）编辑
那么我认为您应该尝试 < a href="http://www.imagemagick.org/script/index.php" rel="nofollow">ImageMagick（或 GD2）。它提供了比 GD 更好的质量。检查这个
By default the quality of the image output from
imagejpegis 75, Try setting it at 100 to get the image at full quality.Check the manual for further details.
Also try using imagecopyresampled. (I think you would have been using
imagecopyresizedsomewhere in your code. Useimagecopyresampledinstead of it. )EDIT
Then I think you should try ImageMagick(or GD2). It gives a better quality than GD . Check this
如果您执行隐写术JPEG 文件格式不太适合隐写术> 逐个像素。
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信息。 jpeg 类型的压缩（有损压缩）是为人类设计的眼睛/大脑保留图像，但不保留文件中的图像位。
您需要使用能够保留像素的图像格式 - 正如您已经编写的那样。这种格式更可能是带有 RLE 压缩的 BMP 或带有 ZIP 或 RLE 的 TIFF 图像格式压缩。这称为无损数据压缩。
The JPEG file format is not very suitable for steganography if you do the steganography pixel by pixel.
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 .
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.
使用
imagepng()而不是imagejpeg()函数并将压缩设置为 0 ：bool imagepng ( resource $image [, string $filename [, int $quality [, int $filters ]]] )请参阅：http://php.net/manual/en/function.imagepng.php
Use the
imagepng()instead of theimagejpeg()function and set the compression to 0 :bool imagepng ( resource $image [, string $filename [, int $quality [, int $filters ]]] )See : http://php.net/manual/en/function.imagepng.php