JPEG file into an array

Hi,

is it possible to convert an JPEG file into an array in Matlab? What about the reverse conversion?

Owen

Answer 1

[Geoff Hayes]

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.

[Image Analyst]

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]

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]

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]

I tried fread() and it gives the 18.6KB size.

Owen