When I try to save my work as JPG file, image becomes over exposed. I found that this is an issue when merging layers with LIGHTEN blend mode. After merging those layers image gets over exposed and I can't make it to be the same like it was before merging. Is there any way to have exactly the same final result as I have in my project? Maybe I should try different step order?
You need to view the file at 100% to get an accurate preview. At any other zoom ratio the preview is not accurate and will be misleading.
You have a lot of very fine detail in your original. The preview, however, is calculated on the basis of on-screen zoom ratio - IOW a downsampled and softened version of the image with most of the detail blurred. This introduces intermediate values not present in the original.
When you merge, the calculation is performed on the full image data, not the downsampled blurry version. Hence the difference.
Always view at 100% to reliably judge previews, especially when you have noise or fine detail like here.
Thank you! Yes, at 100% images looks absolutely the same