JPEG file into an array

2015 3 29
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更新时间：2024 1 17
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Hi,
is it possible to convert an JPEG file into an array in Matlab? What about the reverse conversion?
Owen

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Geoff Hayes
Geoff Hayes 2015-3-29

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Owen - when you read the JPEG image with imread the output from this function is an array. For example,
A = imread('myImg.jpg');
A is a matrix (multi-dimensional array). You can then use imwrite to save the matrix/array as a JPEG.

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Image Analyst
Image Analyst 2015-3-29
But please don't use JPEG for image analysis unless it's absolutely unavoidable. The artifacts can severely limit your accuracy or appearance. Use a lossless format like PNG, BMP, TIFF, or JPEG2000.
Owen
Owen 2015-3-30
移动：DGM 2024-1-17
Thanks. It works, but there is still a problem with size matching. An JPEG file has the following parameters: 18.6KB, 242x379, but with imread() the matrix is 379x242x3 = 275154 bytes. What I expect is something around 18.6K. It seems the matrix doesn’t have the compression. So how to get the compressed matrix of an JPEG file?
Owen
Image Analyst
Image Analyst 2015-3-30
移动：DGM 2024-1-17
You're checking the size on disk, which will always be less. Once it's decompressed and read into a variable in your MATLAB program, it will be its full uncompressed size. To get the compressed matrix, which virtually no one ever does or ever needs to do unless you're writing your own version of imread(), then you'd have to use fread(). Of course it's not an image at that point since you'd need to decompress it.
Owen
Owen 2015-3-31
移动：DGM 2024-1-17
I tried fread() and it gives the 18.6KB size.
Owen

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