I have a series of images and was wondering if there is a possibility to write something in python to apply a contrast and brightness curve Like in the images below.

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CodePudding user response：

You should refer to, for instance, the OpenCV website (you can learn a lot of interesting methods and have a lot of examples on CV problems), here you have some documentation to check:

• 

  The actual code you need only really starts here:

  # Derive Catmull-Rom spline for our X,Y
  res = splines.CatmullRom(yvals, xvals)
  
  # Make LUT (Lookup Table) from spline
  LUT = np.uint8(res.evaluate(range(0,256)))
  
  # Load ramp image as greyscale
  im = cv2.imread('ramp.png', cv2.IMREAD_GRAYSCALE)
  
  # Apply LUT to image
  stretched = cv2.LUT(im, LUT)
  
  # Save result
  cv2.imwrite('result.png', stretched)
  

  That turns this ramp:

  

  into this:

  

  Note that I artificially added a thin red border so you can see the extent of the image on StackOverflow's annoying background.

  ---

  As regards reading a Photoshop Curves file (ACV or .acv), I wrote some code a while back that parses them but I haven't integrated that with the code above - it shouldn't be too hard - you basically save the points from the ACV file and use them to generate the spline for the above code. I leave it below for anyone interested to play with:

  """
  ################################################################################
  fauxtoshop - does some things like Adobe Photoshop
  
  Mark Setchell ([email protected])
  
  Reads, interprets and possibly applies Photoshop files:
  
  - Curves files (*.acv)
  - Levels files (*.alv)
  - Filter Kernel files (*.acf)
  - Hue Saturation files (*.ahu)
  ################################################################################
  """
  
  import sys
  import numpy
  from struct import unpack
  
  def loadFilter(filename):
  
      if filename.lower().endswith('.acv'):
          loadCurvesFilter(filename)
          return
  
      if filename.lower().endswith('.alv'):
          loadLevelsFilter(filename)
          return
  
      if filename.lower().endswith('.acf'):
          loadKernelFilter(filename)
          return
  
      if filename.lower().endswith('.ahu'):
          loadHSLFilter(filename)
          return
  
      sys.exit(f'ERROR: Unknown file extension {filename}')
  
  def loadCurvesFilter(filename):
  
      with open(filename, 'rb') as f:
         version, ncurves = unpack('>HH', f.read(4))
         print(f'File: {filename}')
         print(f'Version: {version}')
         if version != 4:
            sys.exit('ERROR: Cowardly refusing to read version other than 4')
         print(f'Curve count: {ncurves}')
         curves = []
         for c in range(ncurves):
            npoints, = unpack('>H', f.read(2))
            print(f'Curve: {c}, {npoints} points follow:')
            curve = []
            for p in range(npoints):
               y, x = unpack('>HH', f.read(4))
               print(f'Curve: {c}, point: {p}, x={x}, y={y}')
               curve.append((x,y))
            curves.append(curve)
      return curves
  
  def loadLevelsFilter(filename):
      sys.exit("ERROR: Levels filter not yet implemeted")
  
  def loadKernelFilter(filename):
      sys.exit("ERROR: Kernel filter not yet implemeted")
  
  def loadHSLFilter(filename):
  
      with open(filename, 'rb') as f:
         version, usage, pad = unpack('>HBB', f.read(4))
         print(f'File: {filename}')
         print(f'Version: {version}')
         if version != 2:
            sys.exit('ERROR: Cowardly refusing to read version other than 2')
         if usage == 0:
             print('Usage: Hue adjustment')
         else:
             print('Usage: Colorization')
             sys.exit(f'ERROR: Cowardly refusing to apply colorization rather than Hue adjustment')
         MasterHue, MasterSaturation, MasterLightness = unpack('>HHH', f.read(6))
         print(f'Master Hue: {MasterHue}')
         print(f'Master Saturation: {MasterSaturation}')
         print(f'Master Lightness: {MasterLightness}')
         # There follow 6 hextants, each with 4 range values and 3 settings values
         for h in range(6):
             ranges = unpack('>HHHH',f.read(8))
             settings = unpack('>HHH', f.read(6))
             print(f'Hextant: {h}, ranges: {ranges}, settings: {settings}')
             
  ################################################################################
  # main
  ################################################################################
  if __name__ == '__main__':
  
     if len(sys.argv) not in set([2,3]):
        print('Usage: {sys.argv[0]} filter.[acv|ahu|alv|acf] [image]', file=sys.stderr)
        sys.exit(1)
  
     if len(sys.argv) == 2:
        loadFilter(sys.argv[1])
  

  ---

  Note also that you can apply a Photoshop Curves (ACV) file using ffmpeg like this:

  ffmpeg -i input.jpg -vf curves=psfile="curves.acv" output.jpg