I am an InDesigner beginner too and I have been through this before.
Unfortunately, there is no way to make the colours look exactly the same. This happens because the screen produce colours by light emission; red, blue and green combine constructively (which basicaly meand that if we mix all of them, we get the pure white) to form bright and vivid colours. RGB pictures are brighter and more saturated, but the contrast is worse than CMYK because the colour black brighter than it should be.
In CMYK, the colours are produced by light absorption. Cian, magenta, yellow and black combine destructively (if we mix them all, we get black instead) to form a narrow range of colours. One of the pros of CMYK is that the contrast is much better than it is on screen because the black is almost perfect.
There are some steps you may want to try so you can make the colours look the best as they can on paper.
- On Photoshop, open your original RGB PNG file and then press Shift+Ctrl+Y (or go to Visualize > Gamut Warning). This way, you will know the the area affected by colour conversion. Evaluate the areas. You can see if it is mainly highlights, shadows or midtones that are affected and what are the main colours that will change.
Once you know the area that will have the colour shifted, you will know what to do to get the optimised solution.
Convert to CMYK: Image > Mode > CMYK. Reapeat the steps you have already made in order to correct the colour balance in Photoshop. You may want to increase the overall saturation a bit. You can mix the hue and saturation individually for midtones, shadows and highlights using colour balance and channel mixer to correct the affected areas.
Save as the file as TIFF. Use LWZ compression. Use ZIP compression if you are working on a 16 bit/channel space. When you export to PDF in PDFx1a2001, the images are compressed to JPEGs. If you use TIFF, you will have a better final result since the image won't be compressed twice.
Now, let's go to InDesign.
Note: you will need Adobe Acrobat Pro to be installed.
Open your document and insert the CMYK TIFF you edited before.
Go to File > Print... Or press Ctrl+P
Select Adobe PDF as your printer
Click on Settings. A window will open. Find "Adobe PDF" and then click on "Preferences". This particular step may be a bit different for Mac OS users.
You will se the following window:
Figure 1. Adobe PDF vitual printer preferences.
Click on "Edit". I highlighted the button position in yellow.
- Click on Colour. See the picture below. In the first big red circle, there are two menus. In the first one, choose "Convert all colours to CMYK". In the second, there are a bunch of options: perceptive, saturation, absolute and relative. You should choose the which best suits your case. But, this depends on the kind of your image - illustration, photograph, etc. This article is one of the best I found about this subject. There a lot of information about the colour gamut and the differences between RGB and CMYK. Consider reading it so you can know what is your case. For instance, if it is a photograph, you should choose relative colorimetric.
The second red circle is about the Workspace and it is also important. Choose the right CMYK space according to your region. Ask your printer which one is right. If you are not sure, use the Coated FOGRA39. For what I know it is the most used.
Just make sure that you have the same workspace in both colour preferences and standards, figure 3 and 4, respectively, or it won't print.
Figure 2. Adobe PDF printer standards.
Figure 3. Adobe PDF printer colour preferences.
Click on "Save As" so you can use this preset again in the future. Click OK. Now, you should be back to the first window (figure 1). On the first menu, make sure your preset is selected.
Now, you must set your page size. Find the last menu, about page size. Click Add. Enter your page size. Remember you must account the bleed and margins. E.g. A4 + 3mm bleed + 3mm margin should have width of 210 + 6mm (bleed) + 6mm (margin), and so on. Give your page preset a name and click OK. Be sure to select it.
Now, finally, click OK and print!
Remember it will not look exactly the same colour, but at least you will have the best output.
If someone see that I said something wrong or if there is an easier way to do this, please comment. I will be glad to know more about it.
I hope this helps