Insert a text chunk into a png image - linux

Question

I'm looking for a simple command-line tool (on Linux) to insert a text chunk (e.g. copyright) into a png file, resulting in a new png file:
> png-insert-text-chunk "here's my text chunk" < in.png > out.png
Note: by "insert a text chunk", I do not mean "draw some text on the image". I mean: insert the text into the png file as a chunk, in the technical sense. This can be used, for example, to insert a copyright message that isn't displayed on the actual image.

Answer 1

Use ImageMagick's convert and the -set option:
convert IN.png \
-set 'Copyright' 'CC-BY-SA 4.0' \
-set 'Title' 'A wonderful day' \
-set comment 'Photo taken while running' \
OUT.png
The -set option is used to set metadata elements. In the case of PNG these often go into tEXt chunks.

Answer 2

I have searched around for utilities to do this, and not yet found anything that really matches what I want to do. So I decided to build my own, which it turns out is not too hard. The utility png-text-dump displays all text chunks in a PNG image. It depends only on libpng. The utility png-text-append inserts text chunks into a PNG image. It depends only on the standard C library - I had initially tried to implement this using libpng, but actually found it easier to work from scratch using only the PNG specification.

Answer 3

Note: This answer was a response to the original revision of the question where it was not clear if the text had to be written on the image or if the text had to be embedded within the image binary file as metadata. This answer assumed the former. However the question was edited to clarify that it meant the latter. This answer is left intact, in case someone is looking for a solution to the former.
convert -draw "text 20,20 'hello, world'" input.png output.png
The 20,20 in the above example is the co-ordinate where I want to place the text.
You need to use the imagemagick package to get this command.
On Ubuntu or Debian, it can be installed with the command: apt-get install imagemagick.
Here is a slightly more elaborate usage of the command:
convert -font Helvetica -pointsize 20 -draw "text 20,20 'hello, world'" input.png output.png

Answer 4

This can be implemented with python pypng module. The python3 example code is below:
import png
TEXT_CHUNK_FLAG = b'tEXt'
def generate_chunk_tuple(type_flag, content):
return tuple([type_flag, content])
def generate_text_chunk_tuple(str_info):
type_flag = TEXT_CHUNK_FLAG
return generate_chunk_tuple(type_flag, bytes(str_info, 'utf-8'))
def insert_text_chunk(target, text, index=1):
if index < 0:
raise Exception('The index value {} less than 0!'.format(index))
reader = png.Reader(filename=target)
chunks = reader.chunks()
chunk_list = list(chunks)
print(chunk_list[0])
print(chunk_list[1])
print(chunk_list[2])
chunk_item = generate_text_chunk_tuple(text)
chunk_list.insert(index, chunk_item)
with open(target, 'wb') as dst_file:
png.write_chunks(dst_file, chunk_list)
def _insert_text_chunk_to_png_test():
src = r'E:\temp\png\register_05.png'
insert_text_chunk(src, 'just for test!')
if __name__ == '__main__':
_insert_text_chunk_to_png_test()

Answer 5

I believe that pngcrush has this ability: http://pwet.fr/man/linux/commandes/pngcrush

Answer 6

Adding to the comment made by #susam-pal, to change color use the option
-fill color
This option accepts a color name, a hex color, or a numerical RGB, RGBA, HSL, HSLA, CMYK, or CMYKA specification. See Color Names for a description of how to properly specify the color argument.
Enclose the color specification in quotation marks to prevent the "#" or the parentheses from being interpreted by your shell.
For example,
-fill blue
-fill "#ddddff"
-fill "rgb(255,255,255)"
Obtained from link