I converted a bunch of "normal" JPG photos via
convert infile -colorspace Gray outfile
to monochrome. However the result is for all images very dark. Here a sample conversion: original photo and converted monochrome image.
Is there a better way to convert a photo-realistic image with ImageMagick to gray-scale?
The documentation states that when changing the color space, the colors are converted from their original gamma to linear before the conversion. You need to convert them back to an appropriate gamma.
convert infile -colorspace Gray -gamma 2.2 outfile
Related
convert 0101.jp2 -threshold 50% -type bilevel -monochrome -compress LZW ../0101.tiff
The resulting image looks jagged when I use the above command to convert a colored scanned text page to a black/white image (must be one bit per pixel). I want to make it of a higher resolution to look smoother. How can I use convert to do so?
Note that SO automatically converts tif image to jpg format so the output image shown below is not the same as the output image. You will need to run the convert command to get the true output image in tif.
If instead of thresholding you apply a strong contrast the gray pixels on the edge remain in a range of grays and the output is not jagged.
convert Original.jpg -sigmoidal-contrast 30 Corrected.jpg
(there are several ways to increase contrast in Magick)
I am trying to create a PDF file using Latex. However, Latex does not handle TIFF or any other image format capable of both transparency and CMYK. The only solution I think I can use is to convert the PNG image to PDF and embed those in the file.
I am somewhat familiar with imagemagick, however, I am having trouble figuring out how to convert a PNG (probably in the RGB/SRGB colour space) to a PDF in the CMYK colour space.
How do I go about doing this conversion so that the colours are correct and the transparency remains?
In Imagemagick, you should use a CMYK type profile to do the conversion:
convert input.png -profile USWebCoatedSWOP.icc output.pdf
Note, however, that Imagemagick will simply put the raster image into a vector PDF shell. It will not vectorize the image.
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.
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)
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.
My initial input is a colour multi column JPG file. I run image magick on this to create a TIFF file which tesseract 4.0 then performs OCR on to convert the TIFF to a PDF with the text in a searchable form.
Problem with this is because the TIFF output from Imagemagick is monochrome ( which is has to be for tesseract to extract the text correctly ) the final PDF is monochrome with the text highlightable on it. What I am trying to figure out is , is there a way to retain the colour of the original document when Imagemagick converts it to TIFF?
I am running on Ubuntu 14.0
The goal is to start with a coloured JPG image ( book scan but I don't have control over the scan process so always get a JPG ) which has text on it and convert this to a PDF file which looks the same as the JPG but with the text in a searchable/highlightable format.
My imageMagick command to convert the JPG to tiff is
convert -density 300 MyImage.jpg -depth 8 -lat 30x30-5% MyImage.tiff
MyImage.tiff is black and white which works best for Tesseract to to its OCR.
Tesseract command to convert to PDF is
tesseract MyImage.tiff MyImage pdf
But the final PDF will be black and white. What I would want to have is the text overlayed on a colour version of the original JPG.
Tesseract will only give decent results if using a monochrome input tiff file
I created an 8-bit .tiff image ("test.tiff") containing a grid of 30 different color patches in the RGB color space using ImageMagick -convert.
When I convert this image into a jpeg (which is what I need) using:
convert -quality 100 -colorspace RGB -depth 8 test.tiff test.jpg
The identify -verbose command reveals that the resulting jpeg has several additional colors in the color table, each only taking up a few (1-4) pixels and residing very near the desired colors in RGB space. My assumption is that some kind of border bleeding is happening; maybe due to compression?
I don't understand why this border bleeding has occurred, especially given that it does not occur when I convert the tiff image to either a bmp or pcx image.
Thank you
By definition, JPEG is a lossy compression. The effects your experiencing are expected with the JPEG format. Setting the -quality of 100 will not have a 1-to-1 image result as tiff.
See additional answers:
Should I use JPG or TIFF for high-quality prints?
[...] because every time [JPEG] would save it it would generate some changes.
Is Jpeg lossless when quality is set to 100?
At [quality] 100, you just get the LEAST loss possible.
I don't know how you created your 30 colour swatch, or how your histogram looks, but you might try adding -dither None and -colors 30 options to your convert commands:
convert test.tiff -dither None -colors 30 ...