White Balance Merge affects sharpness

[pixelman]

Running latest Affinity Photo on Windows 11.

So I'm editing an image and it looks good except for white balance. I open White Balance (WB) and adjust the Tint. If I click on Merge, the sharpness appears to degrade. If while I'm in the WB window I instead do Document/Flatten the sharpness is not affected.

In the attached example, the top image is the starting point. The next image is a screenshot while the WB window is open. The WB changes but the sharpness is unchanged. The next image is the result of using Merge. The final image is the result of undoing the WB where Merge was used and repeating WB but using Document/Flatten while the WB window is still open.

How to explain?

[NotMyFault]

This is a known issue when the lower layer is not pixel aligned (in essence, you used the move/transform tool on it).

workaround: rasterize the lower pixel layer before any merge down.

 

 

[pixelman]

I'm not sure I understand all this. Is the issue that I resized the image before doing the WB adjustment? As a test, I opened an image, cropped it as before and resized. Before doing WB, I right clicked on the background layer and selected Rasterize. (It was a bit confusing as the menu item is Rasterize... as if another window would open with options but none did). Anyhow, I then did the WB adjustment with Merge and it again blurred the image.

 

[NotMyFault]

Interesting. 
 

Blurring can occur from rasterizing / merging, but not from adjustments. Any chance you can upload an actual document, and provide an exact list of steps (or screen recording showing every single step)?

[pixelman]

I've been trying to provide an example but so far having trouble getting consistent results.

Meanwhile, can you explain why using Merge in the WB window gives different results from using Document/Flatten while the WB window is open? How is Merge different from Flatten?

 

[NotMyFault]

Merge down merges the visible result into the lower pixel layer. This has to be taken literally: in case the layer is rotated by 45 degree, the result keeps this rotation. If pixel position is fractional, all get blurred. If dpi of layer is lower, it will be used. In extreme case, you can create a pixel layer with 1 dpi, and all gets averaged into one single pixel.

all other merge / flatten operation create a new layer, unrotated, and using the canvas size and document dpi.

as a best practice survival tip:

• never use merge down, unless you are absolutely sure it is perfectly pixel aligned, not rotated, and has same dpi as document. 
• or you really know what you are doing.