identifi

#!/bin/sh
#
# This is a simple wrapper for ImageMagick's identify tool.
# It outputs relevant information in an easy-to-understand format.
#
# See also:
# * https://unix.stackexchange.com/questions/406454/how-to-get-the-dpi-of-an-image-file-png
# * https://imagemagick.org/script/identify.php
# * https://imagemagick.org/script/escape.php
# * https://github.com/ImageMagick/ImageMagick/issues/5950

# Using '%[fx:int(resolution.x)]' instead of '%x' to round to an integer.
# Using '%[fx:int(resolution.y)]' instead of '%y' to round to an integer.

# Basic file info:
# %i full filename (%f is just the basename)
# %B file size (bytes)
#
# Basic image info:
# %w width
# %h height
# %m format (JPEG, PNG, GIF)
# %C %[compression] image compression type (JPEG, Zip, LZW)
# %[type] image type (palette, TrueColor)
# %z %[bit-depth] depth (8-bit)
# %[channels] colorspace neumonic followed by total number of channels and meta channels (srgba 5.0)
#
# Optional image info:
# %Q compression quality (useful for JPEG, default=92)
# %[gamma] gamma (default=0.454545)
# %[orientation] orientation
# %x,%y resolution (dpi)
#
# GIF-related:
# %p index of image in current image list (for GIF or other multi-image formats)
# %D image GIF dispose method
# %T image time delay (in centi-seconds)
#
# Not used:
# %k %[colors] number of unique colors (expensive to compute on large images)
# %r %[colorspace]  colorspace (sRGB)
# %[printsize.x] print size (inches?)

COLOR=1

case "$1" in
	--nocolor|--no-color|--nocolour|--no-colour)
		COLOR=0
		;;
esac

if [ "$COLOR" = 1 ] ; then
	RED=""
	BOLD=""
	NORMAL=""
else
	RED=""
	BOLD=""
	NORMAL=""
fi

for f in "$@" ; do
	# `identify` likes to buffer all the output and flush it only upon exit.
	# Calling identify for each file shows the results progressively, which is better UX.
	#
	# Calling it for each file adds some overhead and makes the overall script
	# slower for many files. However, by the time this difference is
	# significant, the user should probably be calling identify directly (with
	# a custom format).
	#
	# Alternatively, I could have used `stdbuf` or `unbuffer`, but that would
	# add one extra dependency on this script, making it less portable.
	# https://stackoverflow.com/questions/11337041/force-line-buffering-of-stdout-in-a-pipeline

	identify -units PixelsPerInch -format "%B*%w*%h*%m*%C*%[type]*%z*%[channels]*%Q*%[gamma]*%[orientation]*%[fx:int(resolution.x)]*%[fx:int(resolution.y)]*%p*%D*%T*%i\n" "$f"
	case "$?" in
		0)
			# No errors.
			;;
		2)
			# Keyboard interrupt, let's abort.
			break
			;;
		*)
			echo "${RED}Error${NORMAL} (exit=$?) identifying $f" > /dev/stderr
	esac
done | awk '
	BEGIN {
		FS="*"
	}
	{
		# For debugging, uncomment this:
		# print $0

		bytes = $1

		width = $2
		height = $3
		format = $4
		compression = $5
		type = $6
		bitdepth = $7
		channels = $8

		quality = $9
		gamma = $10
		orientation = $11
		resolutionx = $12
		resolutiony = $13

		imgindex = $14
		gifdispose = $15
		timedelay = $16 * 10

		filename = $17

		pixels = width * height
		megapixels = sprintf("%.1f", pixels / 1000000)

		out = ""

		if (imgindex > 0) {
			out = out "⤷ " imgindex " "
		}
		if (timedelay) {
			out = out "[" timedelay "ms " gifdispose "] "
		}

		out = out format " " type " " bitdepth "-bit " channels " "

		if (compression == "JPEG" || quality != 92) {
			out = out "(" compression " " quality ") "
		} else if (compression != "Undefined") {
			out = out "(" compression ") "
		}

		out = out width "x" height " pixels " megapixels "MP "

		if (resolutionx > 0 && resolutiony > 0) {
			mm_width = sprintf("%.0f", width * 25.4 / resolutionx)
			mm_height = sprintf("%.0f", height * 25.4 / resolutiony)

			out = out "(" mm_width "x" mm_height "mm "
			if (resolutionx == resolutiony) {
				out = out resolutionx "dpi) "
			} else {
				out = out resolutionx "x" resolutiony "dpi) "
			}
		}

		if (orientation != "Undefined") {
			out = out orientation " orientation "
		}

		if (gamma != 0.454545) {
			out = out gamma " gamma "
		}

		out = out bytes " bytes: " "'"${BOLD}"'" filename "'"${NORMAL}"'"

		print out
	}
'