When doing a 2D to 3D conversion, we need a depth map, which shows us what areas are closer to us, and what are more distant. The white area is located at the foreground, the black one is at the background. The general task is to create an acceptable depth. Sometimes you can make a depth map easy and quickly. Sometimes the images require a serious work on the depth map creating. Look at the flat image attentively to choose the right way for the depth map creation. Let's look, how one can draw a depth map using Adobe Photoshop.
Let's split the fire picture into Red, Green, and Blue channels (open Window -> Channels, and choose the command Split Channels). Look at the Green channel, it's very good depth map for this case. Select it, convert Grayscale into RGB colour mode (Image -> Mode -> RGB colour), and save Green channel as a depth map. Then make Image -> Adjustment -> Auto Contrast.
Don't open the Bas-relief software yet. Set the correct size of image. If you make it too small (e. g. 3x4 cm), Bas-relief chooses a very big parallax automatically. The image with a big parallax will be garbled. If you make the image size too large (e. g. 50x70 cm), the software chooses a very small parallax, and the stereo effect will be hardly noticeable. Set the image size to a value about 20x30 cm. Open the source image in Photoshop, choose Image -> Image size, turn off Resample image (it's very important, because you can't change the image size in pixels), set the necessary image size in centimeters, and save it.
The pixel size of a source image must be equal to the pixel size of a depth map. If you want to change the image size, change the depth map size and the image size simultaneously.
Then run Bas-relief. Open Image, and Depth map.
If you can see the message "I can't calculate the parallax automatically", this means that the image resolution is unknown. In this case, set the Parallax between viewpoints, px manually.
If you have the anaglyphic glasses, you can make anaglyph image for preview. If the image contains bright red or/and bright blue, choose the Grey Red-Cyan option to make a desaturated anaglyphic picture.
Click Anaglyph image, and look at the image. If you want to enlarge the parallax, turn off the Auto option, and set a new value of Parallax between viewpoints, px.
Now we can change the Stereo window position. Move the slider Stereo window position, px to move the stereo window. The highest value of Stereo window position means that the stereo window is located in the foreground, and the lowest one means that the stereo window is located in the background.
Now we want to get several views for a lenticular picture. Set the number of views in the Number of viewpoints, set the viewing angle of the lenticular sheet in the Viewing angle. Click Lenticular viewpoints to create views for lenticular printing.