Quality Degrades When Merging Layers to Save

I'm still convinced this is caused by viewing a noisy/binary image, and not viewing it at 100%. The title, "quality degrades when merging layers", is a giveaway.

100% maps exactly one image pixel to exactly one screen pixel. Any other zoom ratio resamples the image, and any resampling softens and blurs sharp pixel transitions.

The adjustment/blending previews you see on screen as you work, are calculated from the screen image. That's done for performance reasons. If that screen image is a soft, resampled version, you get a lot of intermediate values that aren't really there in the original data. And the calculations are done on this false basis. So you get a misleading preview.

If you view the file at 100% when judging the effect of the adjustment, you don't get this misleading preview. You get a true representation of the pixel data and what the adjustment will really do to them.

In other words - there's no degrading. You just got a false preview, because you didn't view at 100%.

In a normal photograph the effect is negligible and this isn't an issue. But with very noisy data, or "binary" images where pixels are either "on" or "off" (line art, halftone screen etc) - you always need to judge at 100%.

Hi!

I have one more suggestion to add--which has worked well for me over the years. You can use layers to simulate the look of doding and burning and you have complete control over your image and how much dodging and burning are applied.

Create a new layer above the layer that you want to dodge or burn. Set the Blending Mode of that layer to Soft Light. Select your brush (Soft edged brush) and a very low brush opacity--like 6% or a little more. If you use white, you will dodge an area. If you use black, you will burn an area. I have minimized the look of bags under the eyes with this technique for years. You want to build it up slowly, and if you make a mistake you can use the eraser tool on that area and start again.

And, the best part? You have control over it. If it's too much, just lower the opacity of the layer. If it's too little, you can add more. If you don't like what you've done, just throw away the layer and start again. Your image is never degraded. 

I agree with Myra's workflow of making sure you always have your original source image to work on and export the jpg. This will give you the best quality image and keep it looking good.

Let us know if you have any questions,

Michelle

This is probably caused by not viewing at 100% with a noisy or "binary" image. See this thread for a fuller explanation:

https://community.adobe.com/t5/photoshop/jpeg-amp-tiff-saving-from-ps-at-low-quality/td-p/11396914?page=1 

Every time you save an image as a JPEG, the image is getting compressed. And if you're resaving it, it's getting compressed again. There are a couple of options to maintain quality. The first is to merge your layers but save it in a lossless format. When your editing is done you can export a JPEG from that source file. That file will be compressed, but it won't compound the compression, and you can go back to your original file. Another option would be to use a smart object instead of merging your layers. The smart object combines the layers in a wrapper where you can apply certain effects. Unfortunately, the Dodge, Burn, and Clone tools won't work on a smart object unless you rasterize it. What you can do instead is use the Camera Raw Filter (Filter > Camera Raw Filter...). To apply an effect similar to dodging or burning, select the Adjustment Brush on the right and increase or decrease the Exposure using the slider. To clone, select the Spot Removal Brush and make sure the Type is set to Clone. Click OK when you have made your adjustments. You'll see your adjustments applied as Smart Filters in the Layers panel. Another benefit of this method is that it's non-destructive. You can go back and change your adjustments at any time.