CODEWITHSUNDEEP
ruby-on-railsrubyimagemagickrmagickcolor-scheme
marco
marco

Reputation: 33

Ruby + RMagick + base64 image + RGB conversion from GrayScale doesn't work

I'm uploading base64 encoded image to a RoR application. When I receive the image, it has a rgb color scheme (correct), when I write the image on file to be uploaded with paperclip gem, the image color scheme change from rgb to grayscale.

Here is the code:

source = src.gsub(/^data:image\/(png|jpg|jpeg);base64,/,"")
blob = Base64.decode64(source)
img = Magick::Image.from_blob(blob).first
img.colorspace = Magick::SRGBColorspace
img.add_profile "#{Rails.root.to_s}/lib/color_profiles/RGB.icc"
img.write(url = "#{Rails.root.to_s}/tmp/#{self.id}_logo.png")

image = File.open(url)

the img is correctly a RGB image, if I check the resulted created file:

identify -format "%[colorspace]" #{url}

the color scheme is Gray.

Additional info: The uploaded image is all black with white text, if I upload same image with red background, the final image is correctly an RGB image.

Upvotes: 2

Views: 1542

Answers (2)

fmw42
fmw42

Reputation: 53192

There seems to be a bug in ImageMagick 6.9.9.27 and 7.0.7.15 when reporting the conversion of a grayscale image to RGB PNG. Identify -verbose is reporting grayscale but the string format %[colorspace] is properly reporting sRGB as are the PNG tags. I have reported this bug. For example:

convert logo: -colorspace gray logo.jpg
convert logo.jpg PNG24:logo.png
convert logo.png -format "%[colorspace]" info:
sRGB


identify -verbose logo.png
...
Colorspace: Gray
...
png:IHDR.color-type-orig: 2
png:IHDR.color_type: 2 (Truecolor)

Upvotes: 1

fmw42
fmw42

Reputation: 53192

I do not understand. Is your image a color image or a grayscale only image?

IM 6.7.7.10 was during a time that ImageMagick was changing from non-linear gray to linear gray and back again. And also had RGB and sRGB swapped. So you may have a version where gray was linear (darker than non-linear gray) or where RGB and sRGB were swapped. You can convert back to non-linear using one of the following (I do not recall which to use at this time). The other will convert from linear to non-linear. If I assume your input image was grayscale and not color, then try one of these:

convert input -colorspace RGB -colorspace gray result

or

convert input -colorspace sRGB -colorspace gray result

If it is not grayscale, but color only, then leave off the -colorspace gray in these commands.

I would urge you to upgrade if you can. You are well over 200 versions old.

P.S. It is also possible your profile is causing a problem. I don't know what the RGB.icc profile is. Is that an Adobe RGB profile or an sRGB profile.

Can you reproduce your problem using Command Line ImageMagick? If so, post the command line you used. Sorry I do not know Ruby or RMagick.

P.S. 2 Apart from the lighter/darker issue, if you are trying to convert a grayscale image to color, then you will need to specify the output as PNG24:name.png. That is the only way to force a grayscale image to report colorspace=RGB without inserting color pixels.

Upvotes: 0

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