While the best way to view or manipulate image files on Linux is to open them on your desktop for viewing or manipulating with tools like Gimp, there are quite a few ways to get important details on the command line.
Identifying image type by file extension
In general, image files can be identified on the command line by listing their names. Clearly ".jpg" represents a jpeg file, ".png" a portable network graphics file, ".gif" a graphics interchange format file, ".tiff" a tagged image file and so on.
$ ls -l images -rw-rw-r--. 1 shs shs 256093 Jul 15 2018 mycats.jpg -rw-r-----. 1 shs shs 784238 Jul 15 2018 mycats.png -rw-rw-r--. 1 shs shs 6760 Jul 15 2018 arrow.jpg -rw-r-----. 1 shs shs 8853 Jul 15 2018 arrow.png
Nearly all of the time you can rely on file extensions accurately reporting the file type, but there's more you can do with additional commands.
Identifying images with the file command
The file command can identify image file types by extracting data from the files themselves.
$ file Emmy.jpg Emmy.jpg: JPEG image data, progressive, precision 8, 704x584, components 3
The file below is clearly a jpg file in spite of its name. The output from the file command reports this.
$ file camper.png camper.png: JPEG image data, JFIF standard 1.01, resolution (DPI), density 72x72, segment length 16, Exif Standard: [TIFF image data, little-endian, direntries=11, manufacturer=samsung, model=SM-G935V, orientation=upper-left, xresolution=164, yresolution=172, resolutionunit=2, software=GIMP 2.8.18, datetime=2018:04:30 07:56:54, GPS-Data], progressive, precision 8, 3465x2717, components 3
For most jpg files these days, the file command will show a lot more details as in the examples above and below. This output includes the file type, resolution details and quite a bit of information about where the image came from and when it was taken.
$ file tulip_poplar.jpg tulip_poplar.jpg: JPEG image data, Exif standard: [TIFF image data, big-endian, direntries=11, yresolution=146, xresolution=154, model=SM-A526U, height=2448, manufacturer=samsung, software=A526USQS5CVC9, orientation=upper-left, datetime=2022:05:17 19:58:50, width=2448], baseline, precision 8, 2448x2448, components 3
As you can see from the output above, the tulip_poplar.jpg file was taken on May 17, 2022, with a Samsung cell phone,
Viewing image details using an octal dump
You can view some image details using the od -bc (octal dump) command. However, looking beyond the first couple of lines will also display portions of the image itself that won’t be helpful. The first part of the file contains “meta information” (data that describes the content rather than the image content itself). For example, the second line below identifies the file as a png file.
$ od -bc coconuts.png | head -4
0000000 211 120 116 107 015 012 032 012 000 000 000 015 111 110 104 122
211 P N G \r \n 032 \n \0 \0 \0 \r I H D R
0000020 000 000 011 274 000 000 010 257 010 006 000 000 000 017 251 304
\0 \0 \t 274 \0 \0 \b 257 \b 006 \0 \0 \0 017 251 304
Extracting image details using exiftool
Another tool for displaying image metadata is exiftool. In the example command below, we can see extensive details on a png file.
$ exiftool coconuts.png ExifTool Version Number : 12.42 File Name : coconuts.png Directory : . File Size : 5.3 MB File Modification Date/Time : 2023:01:19 16:18:18-05:00 File Access Date/Time : 2023:01:19 16:18:34-05:00 File Inode Change Date/Time : 2023:01:19 16:18:18-05:00 File Permissions : -rw-r--r-- File Type : PNG File Type Extension : png MIME Type : image/png Image Width : 2492 Image Height : 2223 Bit Depth : 8 Color Type : RGB with Alpha Compression : Deflate/Inflate Filter : Adaptive Interlace : Noninterlaced Pixels Per Unit X : 11811 Pixels Per Unit Y : 11811 Pixel Units : meters Profile Name : Photoshop ICC profile Warning : Install Compress::Zlib to read compressed information ICC Profile : (Binary data 2616 bytes, use -b option to extract) White Point X : 0.31269 White Point Y : 0.32899 Red X : 0.63999 Red Y : 0.33001 Green X : 0.3 Green Y : 0.6 Blue X : 0.15 Blue Y : 0.05999 Image Size : 2492x2223 Megapixels : 5.5
The file below was taken in 2016. The details stored within the image file itself are incredibly extensive. It includes not only details about when the photo was taken, but also where it was taken. Note the GPS longitude and latitude measurements near the bottom.
$ exiftool myboy.jpg ExifTool Version Number : 12.42 File Name : myboy.jpg Directory : . File Size : 3.4 MB File Modification Date/Time : 2021:05:25 15:31:09-04:00 File Access Date/Time : 2023:01:01 15:44:38-05:00 File Inode Change Date/Time : 2021:05:25 15:31:09-04:00 File Permissions : -rw-r--r-- File Type : JPEG File Type Extension : jpg MIME Type : image/jpeg Exif Byte Order : Little-endian (Intel, II) Make : samsung Camera Model Name : SM-G935V Orientation : Rotate 90 CW X Resolution : 72 Y Resolution : 72 Resolution Unit : inches Software : G935VVRU2APD2 Modify Date : 2016:06:16 13:54:56 Y Cb Cr Positioning : Centered Exposure Time : 1/245 F Number : 1.7 Exposure Program : Program AE ISO : 50 Exif Version : 0220 Date/Time Original : 2016:06:16 13:54:56 Create Date : 2016:06:16 13:54:56 Components Configuration : Y, Cb, Cr, - Shutter Speed Value : 1/245 Aperture Value : 1.7 Brightness Value : 5.2 Exposure Compensation : 0 Max Aperture Value : 1.7 Metering Mode : Center-weighted average Light Source : Unknown Flash : No Flash Focal Length : 4.2 mm Maker Note Version : 0100 Device Type : Cell Phone Raw Data Byte Order : Little-endian (Intel, II) Raw Data CFA Pattern : Swap Face Detect : Off User Comment : . Flashpix Version : 0100 Color Space : sRGB Exif Image Width : 4032 Exif Image Height : 3024 Interoperability Index : R98 - DCF basic file (sRGB) Interoperability Version : 0100 Sensing Method : One-chip color area Scene Type : Directly photographed Exposure Mode : Auto White Balance : Auto Focal Length In 35mm Format : 26 mm Scene Capture Type : Standard Image Unique ID : C12QSJB01SB GPS Latitude Ref : North GPS Longitude Ref : West GPS Altitude Ref : Unknown (1.7) GPS Time Stamp : 17:54:32 GPS Date Stamp : 2016:06:16 Compression : JPEG (old-style) Thumbnail Offset : 6142 Thumbnail Length : 15400 Image Width : 4032 Image Height : 3024 Encoding Process : Baseline DCT, Huffman coding Bits Per Sample : 8 Color Components : 3 Y Cb Cr Sub Sampling : YCbCr4:2:0 (2 2) Time Stamp : 2016:06:16 13:54:56-04:00 Aperture : 1.7 Image Size : 4032x3024 Megapixels : 12.2 Scale Factor To 35 mm Equivalent: 6.2 Shutter Speed : 1/245 Thumbnail Image : (Binary data 15400 bytes, use -b option to extract) GPS Altitude : 0 m Above Sea Level GPS Date/Time : 2016:06:16 17:54:32Z GPS Latitude : 39 deg 3' 8.04" N GPS Longitude : 78 deg 22' 13.80" W Circle Of Confusion : 0.005 mm Field Of View : 69.4 deg Focal Length : 4.2 mm (35 mm equivalent: 26.0 mm) GPS Position : 39 deg 3' 8.04" N, 78 deg 22' 13.80" W Hyperfocal Distance : 2.14 m Light Value : 10.5
Of course, I'm now very curious about that "Circle Of Confusion" field! More information on the exiftool output is available in an earlier column, What do your photos know about you?
Viewing images in ASCII
Another way to look at images on the command line is to use a tool that displays image content in character format. In others words, the image is displayed as characters and, for some tools, both characters and colors to replicate the image. How well this works will depend on the image itself and the tool you use. One such tool is called img2txt. Had I included the colors in the image below, you would likely be able to recognize the penguin that is waving at you.
$ img2txt penguin.png
@
S8X
S888
8888@88XX8 %@888@
;88%88@@X888tS8 S8888@X
@SS%tS:8 8S8t8@:; ;@8888@8
t8;.;%SXX@888@@88 8S8888888@
88:.;%888@88X: @@ % X88888888@X
%X8;;88S8%X88XS:.S 8 88@8888888@X
X8S%t8 ;:t8.St% 8%.;@ 88@8888888@@
St888X8888@ 8888;888X8 X8X888888888X
;t:X8888888888:888888S@8 X@X88@88@8@@
.S8888888@8@8@888tX% 888 8@88888888@
%@X888@%88SX8X8%@:S88@888 8888888@88
;tSS@8 88.8S888:8@%XS%:88888@@8888@8
SSS%t%S%X8 @888SX@X8%tt88@X8@@8% .%
8XXS%t%tX8: 8XX@88:@;;;tS8%S;%S; :% 8
XX ;%%t%%SXS@8; XX ;X;;;tt%%%%XS .:.%X.S 8
SX8@S%8X%8XS%S%S8X8t;;;8%%%%%%tt;8%.:;;.%@. 888t
X8SX@@%XX%%@Xt%t;;;;8%%%%%%%%tt;;%8 ::.:.:% 8888
Wrap-up
While viewing image files on the command line is not likely to generate deep feelings of nostalgia, you can extract a lot of interesting image details that tell you about the types of images, when and where photos were taken, and what kind of device was used to take the photos.
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