Blend Median problem

Software G'MIC
1

Inspired by Pat David’s article [https://patdavid.net/2013/05/noise-removal-in-photos-with-median_6/ ] about “removing people”
I made five pictures with four chess pieces. The pictures I opened as a layers in Gimp 2.10-Ubuntu 18.04.

Filters> Gmic> Layers>Blend median gave me a sixth image where I hoped that only two of the pieces would be visible.
However, an attentive viewer easily sees that the others remain as ghosts. Using ImageMagick with the terminal command:
“convert *.jpg -evaluate-sequence median OUT.jpg” gave the same result.

Of course I did something wrong, but what?

blended
blended800×533 279 KB
DSC_0795
DSC_0795800×533 316 KB
DSC_0796
DSC_0796800×533 303 KB
DSC_0797
DSC_0797800×533 315 KB
DSC_0798
DSC_0798800×533 304 KB
DSC_0799
DSC_0799800×533 314 KB

2

Hej Alf!

Just a swift idea: might it be that your different shots vary in white balance and exposure?

Have fun!
Claes in Lund, Sweden

2 Likes
3

Yes, clearly, this is due to luminosity variations between all your images.
If you try to ‘normalize’ them a little bit, before applying the median blending, then it works quite well:

$ gmic *.jpeg balance_gamma , blend_median o output.jpg

output
output800×533 89.2 KB

2 Likes
4

@David_Tschumperle and @Claes

Many thanks for your help. It was wonderful that it was possible to fix.

The images were taken with a Nikon D7500, ISO 400, f / 9.0 1/4 sec. White balance auto. I saw for myself now that one picture was significantly darker than the others.

Alf (Norrköping)

5

Hi, I’m trying same command but with tif files. At the end I get an almost white image, few red & yellow pixels in some cases.
[gmic]-15./ Apply gamma-corrected color balance of images [0,1,2,(…),12,13,14], with reference color (128).
[gmic]-15./ Blend images [0,1,2,(…),12,13,14] using ‘median’ mode.
[gmic]-1./ Output image [0] as tif file ‘test1.tif’, with pixel type ‘auto’, no compression and bigtiff support (1 image 4000x6000x1x3).
[gmic]-1./ End G’MIC interpreter.

If I do with the Gimp plug in it works well.

In fact I want to use averge all as it is working on Gimp Plugin when selecting input layers all.

Any idea what I could be doing wrong? Thanks in advance

6

@eadauto Welcome to the forum!

It has to do with how you are saving the image. Please share your command and two sample input files. Drag and drop the files.

7

Hi thanks!

This is the command, I will try to put 2 files in other format as when I put them on tif get really big (140MB)

c:\gmic\gmic.exe -input MDSC_0302_IT1.tif MDSC_0309_IT1.tif MDSC_0316_IT1.tif MDSC_0323_IT1.tif MDSC_0330_IT1.tif MDSC_0337_IT1.tif MDSC_0344_IT1.tif MDSC_0351_IT1.tif MDSC_0358_IT1.tif MDSC_0365_IT1.tif MDSC_0372_IT1.tif MDSC_0379_IT1.tif MDSC_0386_IT1.tif MDSC_0393_IT1.tif MDSC_0400_IT1.tif balance_gamma , blend_median -output test1.tif

8

MDSC_0302_IT1
MDSC_0302_IT11365×2048 1.56 MB
MDSC_0309_IT1
MDSC_0309_IT11365×2048 1.68 MB

9

Median requires at least 3 images. M(4,2,4)=4

10

Works for me. gmic med0.jpg med1.jpg balance_gamma , blend_median o med2.jpg

med2
med21365×2048 1.69 MB

When you save the image, be sure you don’t clip it. E.g., if you do gmic med0.jpg med1.jpg balance_gamma , blend_median * 257 cut 0,255 o med2a.jpg, you get

med2a
med2a1365×2048 155 KB

Since I don’t have your original files, I can’t tell you exactly what to do. The above happens when you save something with a lower range than your data, or your image viewer doesn’t support the bit depth, and so the upper range is clipped.

@Reptorian You may have any number of input images.

11

Then I don’t get why use 2 images for blend median? What’s the median of two number? The average of them?

12

It would be an average of the two middle elements of a sorted list with an even number of elements. If there are only two values, then, yes, you would have their mean. Median - Wikipedia

13

Oh, it seem like I was confusing mode for median for a while. I was fatigued during the last few days.

14

Np, we are here to help each other. Often, when my questions are answered, I realize how obvious it is.

15

Hi, I tried the same with jpg files I posted here and found that the issue is only if I try to save on tif format, if I try png, jpg it works fine. When I try tif it looks like the example you did to break it.
I removed the gamma and other options and it is the same, I guess I’m missing something on the output so tif can work fine.

gmic.exe -input MDSC_0302_IT1.jpg MDSC_0309_IT1.jpg -blend average -output test1.tif
[gmic]-0./ Start G’MIC interpreter.
[gmic]-0./ Input file ‘MDSC_0302_IT1.jpg’ at position 0 (1 image 1365x2048x1x3).
[gmic]-1./ Input file ‘MDSC_0309_IT1.jpg’ at position 1 (1 image 1365x2048x1x3).
[gmic]-2./ Blend all images [0,1] together, using ‘average’ mode and opacity 1.
[gmic]-1./ Output image [0] as tif file ‘test1.tif’, with pixel type ‘auto’, no compression and bigtiff support (1 image 1365x2048x1x3).
[gmic]-1./ End G’MIC interpreter.

Here is the version:
[gmic]-0./ Start G’MIC interpreter.

gmic: GREYC’s Magic for Image Computing.
(https://gmic.eu)

    Version 2.7.4
    Copyright (c) 2008-2019, David Tschumperle / GREYC Lab / CNRS.
    (https://www.greyc.fr)

[gmic]-0./ End G’MIC interpreter.

Will take a look to the link. Thanks a lot

I can’t reply just edit

16

Which G’MIC version (type gmic version) are you using? Also read about saving in the TIF format starting here: Astrophotography - Stacking images with GMIC command line - #2 by afre.