Understanding the pngcheck Command (with examples)
Use Case 1: Print a summary for an image
Code:
pngcheck image.png
Motivation:
You may want to quickly gather basic information about an image, such as its width, height, and color depth.
Explanation:
The pngcheck command with the image path as an argument will print a summary of the image. This includes information like the image dimensions and the number of bits used for each color channel. It provides a quick way to assess important characteristics of the image.
Example Output:
OK: image.png (500x300, 24-bit RGB, non-interlaced)
Use Case 2: Print information for an image with colorized output
Code:
pngcheck -c image.png
Motivation:
Colorized output can make reading the information easier and visually appealing.
Explanation:
The -c option enables colorized output when printing information about the image. This makes it more comfortable to read and interpret the details provided by pngcheck.
Example Output:
OK: image.png (500x300, 24-bit RGB, non-interlaced)
Use Case 3: Print verbose information for an image
Code:
pngcheck -cvt image.png
Motivation:
When you require a more comprehensive understanding of an image’s properties, you can use verbose mode to obtain additional details.
Explanation:
By combining the -c, -v, and -t options, pngcheck provides verbose information about the image. This includes detailed data about the image’s chunks, compression, filter methods, and more. It allows you to delve deeper into the specific aspects of the image.
Example Output:
OK: image.png (500x300, 24-bit RGB, non-interlaced)
Chunk Offset|Chunktype, content
IHDR 0x0000|Width=500 Height=300 BitDepth=8 ColorType=RGB ...
PLTE 0x000D|Red=127 Green=127 Blue=127 ...
IDAT 0x0025| ...
IEND 0x0054|
Use Case 4: Receive an image from stdin and display detailed information
Code:
cat path/to/image.png | pngcheck -cvt
Motivation:
When you want to avoid redundant disk operations or analyze images generated on-the-fly, reading the image data from stdin can be beneficial.
Explanation:
Using cat to stream the image data through a pipe, we can pass the image to pngcheck via stdin. This allows you to analyze the image’s details without first saving it as a file.
Example Output:
OK: <stdin> (500x300, 24-bit RGB, non-interlaced)
Chunk Offset|Chunktype, content
IHDR 0x0000|Width=500 Height=300 BitDepth=8 ColorType=RGB ...
...
Use Case 5: Search for PNGs within a specific file and display information about them
Code:
pngcheck -s image.png
Motivation:
You may want to identify and gather information about all embedded PNG files within another file, such as a document or archive.
Explanation:
The -s option allows pngcheck to search for PNG files within a specified file. It retrieves information about the PNGs found, including their sizes and properties. This is helpful when examining files that could potentially contain multiple PNG images.
Example Output:
File image.png is a PNG image:
Width: 500
Height: 300
Color type: RGB
Bit depth: 8
Compression method: Deflate/Inflate
Filter method: Adaptive
Interlace method: Non-interlaced
Use Case 6: Search for PNGs within another file and extract them
Code:
pngcheck -x image.png
Motivation:
Extracting PNG images from a larger file can be useful for further analysis or manipulation of specific images.
Explanation:
Using the -x option, pngcheck can scan for PNG images within the given file and extract them as individual PNG files. This is valuable when you wish to isolate and work with specific PNG images contained within a larger file, increasing their accessibility.
Example Output:
PNG found and extracted: image1.png (500x300, 24-bit RGB, non-interlaced)
PNG found and extracted: image2.png (200x150, 8-bit grayscale, non-interlaced)
By familiarizing yourself with the various use cases for the pngcheck command, you can efficiently examine PNG, JNG, and MNG files, gather key information, and manipulate images as needed.
