Merging 2 photo's 1 side at the center remains unclear

[snowmansion]

   

When trying to scan a centerfold I usually divide them in 2 separate scans which I then try to merge in GIMP.

I open the 2 scans via File - Open as layers in GIMP and then set the canvassize in such a way they both fit. After aligning them I click on Image and then merging all layers together. 

However this issue I then face is that exactly on the middlepoint one part of the image is vague while the other one seems to have a better clear quality.
See the picture attached.  You see that the right part is more yellow and more clear while the left part is a bit vague. 
How can I change this so that all side have more clarity? I now use the Clone/Heal and sometimes the smudge option, however this is time consuming. Is there any way this can be done automatically?

Thanks in advance.

[zeuspaul]

I would try to match the images before merging. After aligning the images apply curves, contrast, sharpness or ??? to one of the images in an attempt to make it look like the other. Then merge.

[rickk]

(09-26-2022, 06:52 PM)snowmansion Wrote: When trying to scan a centerfold I usually divide them in 2 separate scans which I then try to merge in GIMP.

However this issue I then face is that exactly on the middlepoint one part of the image is vague while the other one seems to have a better clear quality.

I have found that some scanners do not reproduce the entire field with full fidelity. Sometimes towards the edges things become slightly distorted.  So I usually overscan the images so that considerable overlap exists between adjacent panels...and then erase  a portion of the top layer, so that the area of the actual physical splice is not part of the edge of either scan.   For example, for an image 10" wide.... you might scan two 6" wide panels ....each started from opposing sides of the image.   And then erase a potion of the overlap as shown in the below sketch.   Sometimes I find that if the first splice doesn't work well, an undo and subsequent attempt  slightly to one side of the first  often works better

[Ofnuts]

You can use a layer mask to blend the two layers progressively over the width of the overlap.

A possibly easier solution is to not use Gimp but a panorama app such as Hugin. These usually have an option (Parallel scan or whatever) to stitch pictures where the camera/scanner has been translated (instead of rotated like in usual panorama). This will do both the alignment and the luminosity/color adjustments. Rickk'ss remarks still apply though, the scanner will often distort the edge to the right so you can 1) test you scanner and 2) cut out the bad parts before submitting to Hugin.

[rich2005]

I do not think there is an easy solution. When a scanned image covers opposing pages, then there is no overlap and if the page(s) are not absolutely flat on the plattern, then you get that "center-fold-blur" and distortion.

Is there a color difference ?  If you look away from the center they do match.

Not a solution, just an example. Applying a median blur, without center strip, sort of gets you there.

   

   

The only real solution is a better scan or maybe a photograph of the two pages together, not easy.

[snowmansion]

Thank you all for the input.

It seems the issue described by @rickk is also something that I encounter. When trying to align the scans (stitch) they never match. If one part (let's say the top half) is aligned somewhere at the bottom something isn't aligned (especially vivid when you have e.g. a solid line going from the left scan to the right scan). Sometimes I am lucky as the centerpart is just a generic colour (like the sea in this example).

I will try to do as @rickk mentioned trying the capture more area from both sides and try to delete it. Also what I will try to is instead of rotating the magazine 180 degrees for the 2nd scan just keeping it the same orientation but just casually pull it to the left or right to get the other part of the image/scan.

@rich2005 thanks for the input on GIMP I will see how that one works out. @Ofnuts I will look into the Huggin app

[rich2005]

If you have two or more images that overlap then definitely use Huggin