Caroline,
This is a fairly detailed, and thus lengthy, description of a Photoshop process for you to transfer a color palette from one color image to another. I developed this procedure using Photoshop 5.0.2 on Windows 98SE, but hopefully it will work with your Photoshop CS and Windows XP. We will refer to the image that has the color scheme you want to transfer (in this case, your image of a Gauguin painting) as the "donor" image.
(1) First, you will use your "donor" image to create a custom Color Table that captures the desired artistic color scheme. Then you can apply this "artistic" custom Color Table to any image that you wish, and the resulting image will have only those color tones that could be dithered from that particular "artistic" color palette.
(2) To create your custom color table containing those artistic colors, load a copy of your "donor" image into Photoshop and convert it to indexed color via Image > Mode > Indexed Color and on the Indexed Color dialog window, select Palette as Adaptive, leave the Color Depth at 8 bits/pixel (256 colors) and check the Preview box, and for Dither select Diffusion (other selections for Dither might work as well at this stage) and for Color Matching choose "Best". For your case I don’t know whether Preserve Exact Colors should be checked or not, but for this time around, don’t check it. (You can experiment with that later.) Your image window will soon show a preview of the conversion of your donor image to this Indexed Color setup. OK to apply the change.
(3) Now we want to save the Color Table from this donor image. Menu-select Image > Mode > Color Table to open the Color Table dialog box with your Custom color table displayed. Hopefully 256 colors will be displayed, all of which come from your "donor" image.
If a bunch of the colors are black, that is OK, but they indicate room for additions to the table. If the color samples in the color table don’t place the emphasis where you want them, you might want to interrupt the process here and go back and edit your "donor" sample. Say, for example, you want more rose tones to appear in the color table. Just Rubberstamp some rose tones that already exist in your donor image over some of the other colors in the donor image. It doesn’t matter that you are messing up what the donor picture looks like. You are just trying to give some colors more "votes" in the color sampling process. When you think you have skewed the overall color balance in the right direction, save this "Donor Tones" image under a slightly different name and pick up back at Step (2).
(4) Now, let’s say the Color Table looks like a reasonable sample of the donor tone colors you want to use. Click the "Save…" button to open the Save dialog box. Enter a unique name, something like "ArtisticTones1", and click Save (the .ACT file extension will be added automatically.) OK the Color Table dialog to close it.
(5) Now, Open a color image that you wish to make more artistic. It should be in 8-bit RGB Image Mode at this point, and if it isn’t, convert it. Now let’s convert this image to Indexed Color, and apply your ArtisticTones1 color scheme in the process.
(6) Menu-select Image > Mode > Indexed Color… to open the Indexed Color dialog box and on it, for Palette: select Custom… to open the current Custom palette for your image. Click the "Load…" button to open the "Load" dialog box. Select the ArtisticTones1.ACT file (or ArtisticTones2.ACT file if you made an improved one) that you saved previously and click the Load button.
(7) Your selected Artistic Tones color scheme now appears as the current Custom color scheme. OK the Color Table dialog box to accept this color table and to close the dialog box. Now, on the Indexed Color dialog box, the checkmark in the Preview checkbox will have a little flashing underline under it to indicate that Photoshop is busy computing a preview of what your image will look like in this new color scheme.
Depending on how many pixels are in your image, this preview can take several minutes to prepare. It takes a while because Photoshop is doing a lot of work finding a way to best match all of your existing colors using just the colors in your more limited "ArtisticTones1" (or "ArtisticTones2") custom color scheme.
[8] You can wait for the preview to appear, at which time your image’s appearance will change very noticeably and the little flashing underline will disappear. Or, if you are impatient, you can just click OK to accept the change whatever it may be. I recommend you wait for the preview, because the change might be more drastic than you want, and you might want to Cancel and go back and generate an ArtisticTones2 custom color scheme.
(9) If the preview appears acceptable, click OK. Oddly, as soon as you click OK, the image will change noticeably from the preview version (at least it does in Photoshop 5.0.2.) If your zoom level is less than 100% the image may look pretty bad. Zoom in to 100% to see what it actually looks like. (Images in Indexed Color can change their appearance a lot with different zoom levels, but 100% zoom represents the "true" state of the image.) I think you will like the results of Diffusion Dither, but you might want to experiment with "None" for Dither for a posterized look.
(10) Although your image may look pretty good at this point, it is still in the 256-color Indexed Color image mode, with dithering giving the appearance of more color tones, so I recommend you change it back to 8-bit RGB and do something to blend the colors just a little. You could apply a touch of Gaussian Blur, or a little Filter>Noise>Median, or you could change to 16-bit RGB and do an Image Size Bicubic upsample or apply some Image>Adjust operations. There are a lot of ways you could apply a little "finish" to your "Artistic-ized" image.
If you have any questions about this procedure, feel free to ask. I am sure that improvements can be made to the procedure, but I have gotten some pretty good results with the process as described. Modifications to this procedure can produce a lot of interesting artistic image effects, ranging from enhanced duotones to super sepias to psychedelic effects. The real power of the process comes from the intensive color remapping that occurs when you convert to Indexed Color using a custom color table. The process is very versatile because there are so many ways in which you can make a custom color table. (If you investigate the mathematics of it you will see that the actual number of ways is super-astronomical.)
— Burton —
