I have an issue where i have 4 RGB Bitmaps.
Each bitmap contains an image of a single colour
for example
image 1 = Cyan image
image 2 = Magenta image
image 3 - Yellow image
image 4 = black image
I need to find a way to combine the colour data from each image and save as a CMYK formatted file, preferably TIF.
The idea i have had is to create a tiff file at runtime using the CMYK data obtainable from the above images, but the image structure is escaping me.
Any suggestions?
If you can install ImageMagick, it is easy:
convert cyan.bmp magenta.bmp yellow.bmp black.bmp -set colorspace CMYK -combine combined.tif
You can either shell out (using system() and the above command), or link with any of the ImageMagick bindings which include Perl, C/C++, python, php, .Net etc.
It is available, for free, here.
Related
I am trying to convert a LaTeX-generated PDF file to a PNG file with anti-aliasing and a transparent background (white text on a black background). After having read the answer to this post and one of the comments to the answer, I compared the convert function of ImageMagick against pdftoppm. So far, the highest quality anti-aliased images that I can generate are using pdftoppm (for a given DPI resolution). I use the following command:
pdftoppm -png -r 2000 text.pdf > text.png
The equivalent command (or so I think) using ImageMagick was:
convert +antialias -interpolate Nearest -density 2000 text.pdf -quality 90 -colorspace RGB text.png
However, I did not get as good-quality anti-aliasing using ImageMagick as I did with pdftoppm. In fact there hardly seems to be any anti-aliasing in the ImageMagick-generated image. See the close-ups below:
pdftoppm image:
ImageMagick image:
So where this leaves me is that I am satisfied with the anti-aliasing that pdftoppm provides. However, ImageMagick seems to have more functionality in now converting the anti-aliased image such that the black background is transparent. I have applied the approaches detailed in this post using ImageMagick, but they compromise the quality of the anti-aliasing that was previously satisfactory.
Can anyone advise me on how to solve the issue of obtaining a transparent background (which will always be black in color) while not affecting the anti-aliasing quality? Additionally, if the ImageMagick command that I used above was sub-optimal for generating a high-quality anti-aliased image, is there a way that I can achieve both anti-aliasing as well as background transparency by using ImageMagick alone? Any form of advice/tips would be much appreciated!
P.s. Since this question is partially LaTeX-related (I use LuaLaTeX to compile the PDF), I have posted a related question here regarding whether there is a much more straightforward way of directly generating the PDF file with a transparent background.
EDIT:
I've managed to fix the issue of transparency based on some comments on the question I posted on the TeX stack exchange. Now it's just about how I can improve the quality of anti-aliasing. Is there a way that I can achieve the same quality anti-aliasing that I get from pdftoppm?
The pdf file that I am converting can be found on this Dropbox link. Note that the font colour is white, and the background shows as white too (in my pdf viewer anyway), but is transparent. This is the converted PNG file.
You should use -density to increase the anti-aliasing of your PDF to PNG conversion. I note that your image is opaque white and the text is simply in the alpha channel.
convert -density 600 text.pdf -alpha extract x.png
If on Imagemagick 7, change convert to magick.
If you want to keep the transparency and keep your text white, then
convert -density 600 text.pdf y.png
The image is above, but will look completely white and blend with the white background. So you will need to download it.
If you want black text on transparency, then
convert -density 600 text.pdf -alpha extract -alpha copy -channel rgb -negate +channel z.png
Can anyone tell why the image in this pdf does not display as 100% Cyan?
clrtestc - NOPREBLEND32.PDF
Warning: I probably know just enough about pdf and colour to be dangerous!
I'm pretty sure each colour plane of the image is in a separate image. Here's a blended version if that helps.
I know the ColorSpace is DeviceCMYK
I'm pretty sure there is only 100% Cyan in the image, at least there was when it went into the PDF converter.
What went in:
CMYK: 100,0,0,0
RGB: 0,255,255
What I measure coming out:
CMYK: 100,27,0,6
RGB: 0,173,238
I'm foxed! Is there some filter affecting the rendering of the PDF?
There's also Magenta, Yellow and Black versions if they help.
Any help much appreciated.
The PDF file is extraordinarily complicated, it has numerous Forms, some of them nested, most of which are empty. However there only appears to be one image, which is defined in an Indexed CMYK space. So as far as I can see, this is indeed a 100% cyan image.
The extended graphics state does use the Multiply Blend mode, and there is no group and no page group specified, so the colour space used for the blending will depend on the colour model of the output device. If that's a monitor, then it's entirely possible that the resulting output will be RGB.
That's because your CMYK image needs to be converted to RGB in order to be blended using that colour space.
Incidentally, the image is in an Indexed colour space. In your image all the image samples have the same value, that value is then consulted in a lookup table, and that table returns the CMYK components. So no, there is not one image per colour plane, or at least, not in this file.
To be honest, you're going to have to explain better how you are evaluating the content of the PDF file. As far as I can see the image is 100% cyan, and when rendered to a CMYK device, it will remain 100% cyan. If you render to an RGB device, it will be converted to RGB. A poor quality PDF consumer might decide to convert to RGB in the absence of a defined colour space for the blending operation.
Since the blending mode doesn't actually do anything (there's no defined alpha, SMask or any other transparency in the file) you could remove that and see if it sorts out your problem.
Edit
Your screen will be an RGB device, so no matter what the CMYK values in the PDF file are, there won't be any CMYK in the screenshot. The PDF rendering engine will have to convert the CMYK to RGB.
So the PDF rendering engine performs an opaque CMYK->RGB conversion. Then you take a picture of that RGB screen. You load that into an image editing application, and ask it what the RGB values are and presumably what it thinks are the CMYK equivalents.
If the CMYK->RGB calculation that the PDF viewer performs is not the inverse of the calculation that the RGB->CMYK image application performs, then you won't be getting the right values!
There's no way to predict what the RGB intermediate values 'should' be, because there is no 'right' answer here. Fundamentally this isn't a reliable technique for evaluating the colour.
It's hard to make any kind of recommendation without knowing what you are trying to achieve (and possibly why), and what tools you are prepared to use. I believe Acrobat Pro would allow you to look at the colour values directly for example. Or you could use something like Ghostscript to create a CMYK TIFF file, then open that in an image application which supports CMYK (like Photoshop) and look at the values there.
But rendering to the screen, taking a screenshot and trying to figure out what the CMYK values might or might not have been is not really going to work.
I'm trying to use dcraw on a color image (e.g.CR or NEF) to extract raw monochrome data for image processing.
With parameters -4 -D -c I get an image with a checkerboard as shown below:
When unzoomed, the image data is correct, except for the checkboard pattern in all images from different cameras.
The above image was produced using -T and zooming in the resulting .tiff file in File Viewer Plus. In practice, I'm reading the .pgm file directly and getting the same checkboard.
What aren't I understanding? Does this have something to do with Bayer filtering?
Yes, this is due to Bayer filtering and no demosaicing. For example, Green areas will have green pixels brighter than red according to the Bayer pattern, whereas red areas will have green pixels dark.
To get some kind of correct grayscale (or color) image, intensity has to be weighed over a 2x2 area (in standard Bayer). What you are looking for cannot be achieved without the demosaicing step.
Your best bet is to extract a color image, then turn it into grayscale.
I have no experience on any image processing/editing tool. And I am doing a project, which requires me to use different shapes. I could create different shapes using visio. But however not able to get rid of white background behind. I need only shape not squared white background.Tried online out of my ways but not successfull.
Any help will be greatly appreciated.
Thanks,
Ganesh
Absolutely any image file has to be contained within a rectangular frame, this includes png and SVG.
Some image file formats can have what are called alpha channel backgrounds this allows you to see through transparent areas.
What you want to do is remove the white background to expose the alpha channel background in Photoshop (or similar tool) which can then be saved out as transparent.
For example in Photoshop:
If you open this image directly and have no other layers, double click the layer that says background and OK the confirmation box. This turns your flat image into a layered image
Select the magic wand tool and ensure you have a high tolerance set (3)
with the wand selected click the white area to bring up a marquee around your selection (the white background) and hit delete to remove it.
Your image should now have a chequered background which is the transparency showing through.
If you now go to file > save as and select png, your image should now be saved out with an alpha background.
Please note: There are further optimisations to make if this is for web, including file formats and file size but that is beyond the scope of this question but I encourage you to read up on the Gif format and it's restrictions, the difference between 8bit and 24bit pngs and how to use SVG.
You can do it pretty simply at the command-line using ImageMagick which is free and installed on most Linux distros and is available for OSX and Windows.
Basically, you want to make your whites transparent, so you would do
convert shape.png -transparent white result.png
If your whites are a little bit off-white, you could allow for some variation with a little fuzz as follows:
convert shape.png -fuzz 10% -transparent white result.png
I added the checkerboard background just so you can see it on StackOverflow's white background - it is not really there.
By the way, you may like to trim to the smallest bounding rectangle while you are there:
convert shape.png -fuzz 10% -transparent white -trim result.png
By the way, you can also draw your shapes with ImageMagick:
convert -size 150x150 xc: -fill none -stroke "rgb(74,135,203)" -draw 'stroke-width 90 ellipse 0,0 80,80 30,80' arc.png
See Anthony Thyssen's excellent examples here.
I'm using matplotlib to generate some composite figures (from raw data and images). I'm trying to get the script to take image files of a few file formats, which are then plotted via:
Nxy = mpimg.imread(Nxy_filename)
imgplot = ax1.imshow(Nxy)
where ax1 is the subplot I want the image to show up in. This works fine for both PNG and JPEG images, but for a .bmp (of the same image) matplotlib seems to turn it blue, i.e.
turns into:
in my composite figure. On the other hand, the png and jpg files look exactly the same as the original. Any idea why this would happen? I'm reluctant to blindly alter the color map in the code since the other image formats appear as expected.
It sounds like your PNG and JPEG images are RGB images that happen to be grey while the BMP image is grey scale. Check the shape of Nxy. My guess is it's two dimensional for the BMP while the PNG and JPEG image arrays have three dimensions.