[contains fix] With no output filename given, output format of scans ignores -x / --compression option and is solely determined by -m / --mode where -m color produces JPGs and -m gray produces PNGs

I have tried this with 3.17.11 which I've been running until now and have installed (latest) 3.18.6 today where the issue persists.

When no output file is specified (-o), the output file format isn't picked according to the compression chosen but according to the mode (color or gray).

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$ hp-scan -m gray -x jpeg
will produce a PNG file.

Output:

Mode: gray
Compression: JPEG
...
Setting output format to PNG for greyscale mode.

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$ hp-scan -m gray
will produce a PNG file.

Output:

Mode: gray
Compression: JPEG
...
Setting output format to PNG for greyscale mode.

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$ hp-scan -m color -x raw
will produce a JPEG file.

Output:

Mode: color
Compression: None
...
Setting output format to JPEG for color/lineart mode.

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$ hp-scan -m color
will produce a JPEG file.

Mode: color
Compression: JPEG
...
Setting output format to JPEG for color/lineart mode.

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This is confusing.

I went over to `/usr/share/hplip/scan.py` and the mistake seems to be here:

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        if 'file' in dest and not output:
            log.warn("File destination enabled with no output file specified.")

            if adf:
               log.info("Setting output format to PDF for ADF mode.")
               output = utils.createSequencedFilename("hpscan", ".pdf")
               output_type = 'pdf'
            else:
               if scan_mode == 'gray':
                  log.info("Setting output format to PNG for greyscale mode.")
                  output = utils.createSequencedFilename("hpscan", ".png")
                  output_type = 'png'
               else:
                  log.info("Setting output format to JPEG for color/lineart mode.")
                  output = utils.createSequencedFilename("hpscan", ".jpg")
                  output_type = 'jpeg'

            log.warn("Defaulting to '%s'." % output)

        else:
            try:
               output_type = os.path.splitext(output)[1].lower()[1:]
               if output_type == 'jpg':
                  output_type = 'jpeg'
            except IndexError:
               output_type = ''

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To get PNG files in colour mode I *have to* specify an output filename with .png extension manually.

The -x/--compression option has virtually no effect, because the output filename solely relies on either the -o option or the -m option.

In the above code this:

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               if scan_mode == 'gray':
                  log.info("Setting output format to PNG for greyscale mode.")
                  output = utils.createSequencedFilename("hpscan", ".png")
                  output_type = 'png'
               else:
                  log.info("Setting output format to JPEG for color/lineart mode.")
                  output = utils.createSequencedFilename("hpscan", ".jpg")
                  output_type = 'jpeg'

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should be changed so something like this

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               if scanner_compression == 'jpeg':
                  log.info("Setting output format to JPEG.")
                  output = utils.createSequencedFilename("hpscan", ".jpg")
                  output_type = 'jpeg'
               else:
                  log.info("Setting output format to PNG.")
                  output = utils.createSequencedFilename("hpscan", ".png")
                  output_type = 'png'

----------------------------------------

Which I have tested and works.