How to global balance contrast of mosaiced image.

[shivamchaubey]

Hello @jcupitt

I have used merge function to stitch the image. Is there any function to global balance the final mosaiced image. As you can see in the attached image contrast is not balanced in each tile.

I know there is a function globalbalance in pyvips but it works with only mosaiced function. Is there any way to do balancing using merge function or any other way?

[jcupitt]

Yes, global balance will work on merged images too.

You might need to run it in sections, so balance 10x10 blocks of tiles, then balance again after final assembly.

[shivamchaubey]

Can you give please an example to integrate this with merge function?
My code looks like.

1. def stitch(coor):
2.     global onlyfiles,mypath,row,column
3.     onlyfiles=np.array(onlyfiles)
4.     files=onlyfiles.reshape(row,column)
5.     blend=False
6.     for r in tqdm(range(files.shape[0])):    
7.         c=0
8.         if r==0:
9.             tile = pyvips.Image.black(coor[r,c][0],coor[r,c][1])
10.         else:
11.             tile = pyvips.Image.black(coor[r,c][0],coor[r,c][1]-coor[r-1,c][1])        
12.         for c in tqdm(range(files.shape[1])): 
13.             tile1 = pyvips.Image.new_from_file(join(mypath,files[r][c]), access="sequential")
14.             if r==0:
15.                 x,y=coor[r,c]
16.             else:
17.                 x,y=coor[r,c][0],coor[r,c][1]-coor[r-1,0][1]
18.             tile = tile.merge(tile1, 'horizontal', -x, -y, mblend =blend)
19.         if r>0:
20.             y=coor[r-1,0][1]
21.             stitch_img = stitch_img.merge(tile, 'vertical', 0, -y, mblend =blend)    
22.         else :
23.             stitch_img=tile
24.     print (stitch_img.width,stitch_img.height,"width","height")        
25.     stitch_img.dzsave('test_80X80')

I have tried inserting tile=tile.globalbalance() at line number 19 for adjacent contrast adjustment , and also stitch_img=stitch_img.globalbalance() at line number 22 for contrast adjustment between each row. It's not working and I am getting an error.

Error:

raise Error('unable to call {0}'.format(operation_name))
pyvips.error.Error: unable to call globalbalance
im_global_balance: unable to open "temp-0"

Please provide an example for this function.

[jcupitt]

Don't use black, it'll get confused.

You need to start from a set of images on disc, merge them together, then call globalbalance.

[shivamchaubey]

How those black pixels can be ignored. I have added 255 value to those pixels but it's not working with global balance. I can't remove those black pixel area, however, I can modify them to work for global balance. What kind of modification is needed for global balance?

[jcupitt]

You don't need black to assemble a mosaic, do you? Build it without using black and globalbalance should work.

[shivamchaubey]

Whenever I am using merge function, I will have some black pixels because my image is shifting in vertical direction also. So, an extra region is padded with a black pixel. I was using a black image for the first merging operation to make coordinates easy otherwise I have to make dynamic coordinates for merging operation, which is related to the input frame of reference.