Encoding image data as UTF-8 string with gzip compression - ruby-on-rails

Question

I am trying to store image data from a file into a PostgreSQL database as a base64 string that is compressed by gzip to save space. I am using the following code to encode the image:
#file = File.open("#{Rails.root.to_s}/public/" << #ad_object.image_url).read
#base64 = Base64.encode64(#file)
#compressed = ActiveSupport::Gzip.compress(#base64)
#compressed.force_encoding('UTF-8')
#ad_object.imageData = #compressed
When I try to save the object, I get the following error:
ActiveRecord::StatementInvalid (PG::Error: ERROR: invalid byte sequence for encoding "UTF8": 0x8b
In the rails console, any gzip compression is outputting the data as ASCII 8-BIT encoding. I have tried to set my internal and external encodings to UTF-8 but the results have not changed. How can I get this compressed data into a UTF-8 string?

Answer 1

This doesn't make much sense for a number of reasons.
gzip is a binary encoding. There's absolutely no point base64-encoding something then gzipping it, since the output is binary and base64 is only for transmitting over non-8bit-clean protocols. Just gzip the file directly.
Most image data is already compressed with a codec like PNG or JPEG that is much more efficient at compression of image data than gzip is. Gzipping it will usually make the image slightly bigger. Gzip will never be as efficient for image data as the loss-les PNG format, so if your image data is uncompressed, PNG compress it instead of gzipping it.
When representing binary data there isn't really a text encoding concern, because it isn't text. It won't be valid utf-8, and trying to tell the system it is will just cause further problems.
Do away entirely with the base64 encoding and gzip steps. As mu is too short says, just use the Rails binary field and let Rails handle the encoding and sending of the binary data.
Just use bytea fields in the database and store the PNG or JPEG images directly. These are hex-encoded on the wire for transmission, which takes 2x the space of the binary, but they're stored on disk in binary form. PostgreSQL automatically compresses bytea fields on disk if they benefit from compression, but most image data won't.
To minimize the size of the image, choose an appropriate compression format like PNG for lossless compression or JPEG for photographs. Downsample the image as much as you can before compression, and use the strongest compression that produces acceptable quality (for lossy codecs like JPEG). Do not attempt to further compress the image with gzip/LZMA/etc, it'll achieve nothing.
You'll still have the data double in size when transmitted as hex escapes over the wire. Solving that requires either the use of the PostgreSQL binary protocol (difficult and complicated) or a binary-clean side-band to transmit the image data. If the Pg gem supports SSL compression you can use it to compress the protocol traffic, which will reduce the cost of the hex escaping considerably.
If keeping the size down to the absolute minimum is necessary, I would not use the PotsgreSQL wire protocol to send the images to the device. It's designed for performance and reliability more than absolutely minimum size.