it is gone finished flattened
Undo (Ctrl+Z)- even if you have saved the image after flattening. But undo undoes the operations stack so if you did other things to the image after flattening then you will have to undo all those before you can undo the flattening. This will not work if you close the image after saving!
Flattening layers just merges all layers down into one. It reduces file size, but once the image is saved and Photoshop is closed, you will no longer be able to undo the change and edit those layers separately.
Adjustment layers calculate or show you only preview how image will look if you decide to export it with applied adjustment. When using Adjustment layers you are not working with pixels and everything can be changed at any time till image is in PSD format (or layered TIFF). You can change Adjustment later or even delete it without affecting pixels in image in other words same as nothing was happen.
All Layers will be flattened in other words all layers becomes one composite layer. You wont lose any image detail but you will lose ability to work with layers independently.
A flattened image has only one layer. After the image is flattened, it has the same appearance it had before. The difference is that all of the image contents are in a single layer without transparency. If there are any areas which are transparent through all of the layers of the original image, the background color is visible. By flattening an image we introduce significant changes to the structure of the image. It is normally only necessary when you would like to save an image in a format which does not support levels or transparency (an alpha channel).
To Flatten your Layers in Photoshop simply go Layer>Flatten. I recommend saving your image as a psd before you flatten so that you can refer back to your layers. Then flatten and save as a jpg.
Once the image is saved out with the effects, they cannot be undone, but if you haven't closed the program yet, you can either select "Undo" (can only be done with one step) or "Step Backward" (multiple steps) from the Edit menu until you have undone the effect you want to remove, or you can click in the History pallete on the step before the undesirable effect.Note that if you were to use Adjustment Layers in the Layers pallete, all you need to do is toggle that layer's visibility to off to undo the effect. Before using an Adjustment layer though, be aware that Adjustment Layers effect all layers below it, not just one.
Coarse adjustment
When you move the coarse adjustment knob on a microscope, it raises or lowers the stage quickly, allowing you to bring the specimen into rough focus. This knob is used to make large adjustments to the focus of the image.
In Photoshop, you can view both grayscale and RGB images simultaneously by using layers and adjustment layers. You can create a grayscale layer or adjustment layer on top of an RGB image, allowing you to see the color image beneath while applying grayscale effects. Additionally, you can use the "Channels" panel to toggle between color channels and view them in grayscale. This feature is useful for comparing tonal values and color information side by side.
The adjustment knob is a component of a microscope that focuses the image of the object being studied. It is used in conjunction with the coarse adjustment knob.
Open the Layers window.