greyscale

March 20, 2003, 11:44

I have a paper with lots of colorful CFD results thats been accepted for journal that requires gray scale conversion. Simple grayscale conversion in adobe photoshop causes blue and red to be black. Anyone know how to convert to gray scale based on visual spectrum - i.e., blue gets mapped to black, greens to grey and red to white? Thanks Rob

March 20, 2003, 11:58

Gimp should be able to do it.

March 20, 2003, 14:34

I've used ImageMagick and it's worked well for me.

March 20, 2003, 15:54

Thanks Phil, but when I try the ImageMagic utility:

convert -monochrome fn1 fn2

I get the same problem. Both reds and blues are dark.

March 21, 2003, 13:59

Rob,

Reds and blues will be "dark", but they should be discernibly different shades of "darkness"... at least that's what I've found when I convert to grayscale.

What I do is fire-up "display" from imagemagick and load the image that I want to convert. Then I follow the dialog path: Enhance/Grayscale. Try it and see what you get. I think that it will depend somewhat on the shades of red and blue in your original color image. Also, after you convert to grayscale, you could try "Enhance/Negate" to go "reverse-video" and see if that looks better (I've done this also).

Another possibility (if you can regenerate your images) is to change the color-map when you generate the images in the first place.

Another possibility is to take your existing image and alter the color map to some other sequence of colors, and then convert to grayscale. You'd have to play with this one until you get something you like.

I like the idea that Praveen suggested of using the GIMP. It's free with most (if not all) Linux distributions, but may take a little while to get used to, if you haven't already used it.

As far as other possibly ideas... I'm still thinking.

Phil

March 21, 2003, 15:27

Thanks again Phil: Basically Photoshop does the same thing, and I found this to be unsatisfactory. Since my data is long gone I had to manipulate a bunch of images. What I ended up doing was converting to "Indexed Color" with 16 colors in Photoshop. Then I can reassign a "color" to each. I simply choose varying rgb scales from black (0 0 0) to white (255 255 255). That worked pretty well but was tedious. See ya Rob

March 20, 2003, 11:44	greyscale	#1
Rob Kunz Guest Posts: n/a	I have a paper with lots of colorful CFD results thats been accepted for journal that requires gray scale conversion. Simple grayscale conversion in adobe photoshop causes blue and red to be black. Anyone know how to convert to gray scale based on visual spectrum - i.e., blue gets mapped to black, greens to grey and red to white? Thanks Rob

March 20, 2003, 11:58	Re: greyscale	#2
Praveen Guest Posts: n/a	Gimp should be able to do it.

March 20, 2003, 14:34	Re: greyscale	#3
philip buelow Guest Posts: n/a	I've used ImageMagick and it's worked well for me.

March 20, 2003, 15:54	Re: greyscale	#4
Rob Kunz Guest Posts: n/a	Thanks Phil, but when I try the ImageMagic utility: convert -monochrome fn1 fn2 I get the same problem. Both reds and blues are dark.

March 21, 2003, 13:59	Re: greyscale	#5
Philip Buelow Guest Posts: n/a	Rob, Reds and blues will be "dark", but they should be discernibly different shades of "darkness"... at least that's what I've found when I convert to grayscale. What I do is fire-up "display" from imagemagick and load the image that I want to convert. Then I follow the dialog path: Enhance/Grayscale. Try it and see what you get. I think that it will depend somewhat on the shades of red and blue in your original color image. Also, after you convert to grayscale, you could try "Enhance/Negate" to go "reverse-video" and see if that looks better (I've done this also). Another possibility (if you can regenerate your images) is to change the color-map when you generate the images in the first place. Another possibility is to take your existing image and alter the color map to some other sequence of colors, and then convert to grayscale. You'd have to play with this one until you get something you like. I like the idea that Praveen suggested of using the GIMP. It's free with most (if not all) Linux distributions, but may take a little while to get used to, if you haven't already used it. As far as other possibly ideas... I'm still thinking. Phil

March 21, 2003, 15:27	Re: greyscale	#6
Rob Kunz Guest Posts: n/a	Thanks again Phil: Basically Photoshop does the same thing, and I found this to be unsatisfactory. Since my data is long gone I had to manipulate a bunch of images. What I ended up doing was converting to "Indexed Color" with 16 colors in Photoshop. Then I can reassign a "color" to each. I simply choose varying rgb scales from black (0 0 0) to white (255 255 255). That worked pretty well but was tedious. See ya Rob