convert -resize results in 4x the filesize??

[magick]

Add -colors 256 to your command line to create a colormapped image or -monochrome to create a bilevel image. For bilevel images, add -compress group4 to compress the image.

[anthony]

For the actual cause... -resize merges pixels or expands pixels to produce a 'good' quality resize of the image. However all those extra colors will make the 'type' of image different to accomidate all those extra colors.

-colors remaps all the color down to 256 colors (See IM Examples Color Quantization)

-monocromes quantizates the image to two greyscale colors then remaps those two colors
to black and white.

-compress just specifies a different file compression method, probably not what you want.

instead of -resize you can use -scale, which will resize the image by removing rows and columns of pixels rather than merging them. As such no change in the number of colors is produced (actually you may get fewer colors) but the image will not look as good.

[anthony]

Note TIF is not a good format as few programs understand all its internal formats. If -colors is corrupting it then your application does not understand that format.

We will probbaly need to know more about the precise format of the TIF needed.

[glennrp]

If you are reluctant to show us one of your actual images, just post the result of "identify -verbose file.tif" (for the input and output tiffs) and maybe we can get an idea why you are getting the large filesizes. Most likely you are adding colors.