已知尺寸的JPEG图像的最大文件大小 [英] Maximum file size of JPEG image with known dimensions

问题描述

我将允许用户上传使用JPEG压缩的300x300图像.有没有办法确定此类图像的最大文件大小?

I'm going to let users upload images of 300x300 compressed with JPEG. Is there a way to determine what the maximum file size of such an image would be?

我可以想象这可以通过以100质量压缩随机噪声来尝试，但是有理论上的最大值吗?

I can imagine this can be tried by compressing random noise at 100 quality, but is there a theoretical maximum?

假设图像是完全不可压缩的随机噪声，是否可以是每个像素3个字节(24位彩色)和元数据的余量?还是压缩后的图像会比原始图像大?

Say that the image is totally uncompressable random noise, could it be 3 bytes per pixel (24-bits colour) and a margin for the metadata? Or could such an image turn out larger than the original when compressed?

推荐答案

来自维基百科:

对于最高质量的图像(Q = 100)，每个彩色像素大约需要8.25位 ^{http://en.wikipedia.org/wiki/JPEG#Sample_photographs}

For highest quality images (Q=100), about 8.25 bits per color pixel is required ^{http://en.wikipedia.org/wiki/JPEG#Sample_photographs}

因此，对于300x300图像上的Q=100，将导致(300 * 300) px * 8.25 bits/px = 742,500 bits = ~ 93 kB

So, for Q=100 on an 300x300 image, that would result in (300 * 300) px * 8.25 bits/px = 742,500 bits = ~ 93 kB

还有无损的JPEG编码模式，实际上不使用^{(最后句子，第二段)}.但它们将具有典型的RGB 24 bits/pixel.

There are also lossless JPEG coding modes, which are practically not used ^{(last sentence, second paragraph)}. But they would have the RGB typical 24 bits/pixel.

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