image is grayscale or colour?

• hisoka

  12 Sep 07, 16:42

  A question about image processing/analysis i came across.
  
  how to tell if an image is grayscale or colour.
  
  any ideas?
  
  the image is given in a pdf. or jsut a generic image.
  
  of course i guess if it was in a compressed format then we can just query the compression format and values.
  
  edit: add in question on feedback from eagle
• eagle

  12 Sep 07, 16:49

  this question hor, should be asked to ndmmsmallant
  
  I didn't take any modules in image processing techniques
  
  Finally, I don't see any question except "any ideas?"
• hisoka

  12 Sep 07, 17:08

  Originally posted by eagle:

  this question hor, should be asked to ndmmsmallant
  
  I didn't take any modules in image processing techniques
  
  Finally, I don't see any question except "any ideas?"

  question in topic mah.
  
  anyway how to tell if an image is grayscale or colour.
• ndmmxiaomayi

  12 Sep 07, 17:43

  Not too sure how to tell.. but as far as I know, any file that is converted to PDF is most likely intact... that means there's no change in colours or whatever. Unless it has been purposely converted to greyscale...
  
  That will need an image processing program to find out if it has been edited before.
  
  US do this a lot... I can't find the Blackhat presentation on it.
• hisoka

  12 Sep 07, 17:51

  Originally posted by ndmmxiaomayi:

  Not too sure how to tell.. but as far as I know, any file that is converted to PDF is most likely intact... that means there's no change in colours or whatever. Unless it has been purposely converted to greyscale...
  
  That will need an image processing program to find out if it has been edited before.
  
  US do this a lot... I can't find the Blackhat presentation on it.

  hmmz, so is look at the coding of the pdf to find out arh?
  
  any ideas if say given an image find out if grayscale or colour?
• ndmmxiaomayi

  12 Sep 07, 18:02

  Originally posted by hisoka:

  hmmz, so is look at the coding of the pdf to find out arh?
  
  any ideas if say given an image find out if grayscale or colour?

  Probably not directly as a PDF file. The image will need to be extracted out. If it's greyscale, in a hex editor, it's nearly all 0 or Fs. Grey is derived from black... so as it goes lighter, Fs are added.
  
  A hex editor will help.
• hisoka

  12 Sep 07, 18:34

  Originally posted by ndmmxiaomayi:

  Probably not directly as a PDF file. The image will need to be extracted out. If it's greyscale, in a hex editor, it's nearly all 0 or Fs. Grey is derived from black... so as it goes lighter, Fs are added.
  
  A hex editor will help.

  hmmz okz, thx.
  
  any others? me abit blur haha
• eagle

  12 Sep 07, 18:52

  if you have the image
  
  open with adobe photoshop
  
  Go image-> mode
  
  you will see whether it is RGB or grayscale
• ndmmxiaomayi

  12 Sep 07, 20:00

  Originally posted by hisoka:

  hmmz okz, thx.
  
  any others? me abit blur haha

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