Unable to read image using readJPEG in R

Question

I have a column in my R dataframe that contains link to images. eg. https://storage.googleapis.com/du-prd/books/images/9781668001226.jpg

When I try to read it using readJPEG it's giving below error-

"unable to open https://storage.googleapis.com/du-prd/books/images/9781668001226.jpg"

So I tried running it separately to check what's happening and it gives the same error.

readJPEG("https://storage.googleapis.com/du-prd/books/images/9781668001226.jpg")

I'm not sure how to debug this as there's not much detail provided in the error message.

Allan Cameron · Accepted Answer · 2024-01-18 23:43:41Z

3

Since the function takes a raw vector, we can avoid having to write to disk by using readBin to read the jpeg as a raw vector directly from the url, and passing this to readJPEG:

img <- "https://storage.googleapis.com/du-prd/books/images/9781668001226.jpg" |>
  readBin("raw", 1e6) |>
  jpeg::readJPEG()

Now img is an rgb array, so we can do, for example:

plot(as.raster(img))

edited Jan 18, 2024 at 23:43

answered Jan 18, 2024 at 23:36

Allan Cameron

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r2evans · Accepted Answer · 2024-01-18 22:48:49Z

3

That function does not take URLs.

From ?jpeg::readJPEG:

Usage:

     readJPEG(source, native = FALSE)
     
Arguments:

  source: Either name of the file to read from or a raw vector
          representing the JPEG file content.

  native: determines the image representation - if ‘FALSE’ (the
          default) then the result is an array, if ‘TRUE’ then the
          result is a native raster representation.

Fixed code:

tf <- tempfile(fileext = ".jpeg")
download.file("https://storage.googleapis.com/du-prd/books/images/9781668001226.jpg", tf)
# trying URL 'https://storage.googleapis.com/du-prd/books/images/9781668001226.jpg'
# Content type 'image/jpeg' length 40093 bytes (39 KB)
# ==================================================
# downloaded 39 KB
stuff <- jpeg::readJPEG(tf)
class(stuff)
# [1] "array"
unlink(tf) # if you want/need to clean up the temp file

answered Jan 18, 2024 at 22:48

r2evans

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3 Comments

Colombo Over a year ago

Shame that even url(url_address) doesn't work :/

Allan Cameron Over a year ago

@Colombo no, but readJPEG(readBin(url_address, "raw", 1e6))) does.

Colombo Over a year ago

@AllanCameron Nice one!

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