png - What's the point of converting RGB images to CMYK TIF/TIFF before placing them in InDesign?

Currently we receive CMYK TIF/TIFF images of photographs from our design agency (who get them from the photographer). Our in-house designers then place them in InDesign for posters and magazines, or convert them to RGB to be used on the website or in newsletters or presentations.

I'm wondering what's the point of taking a photograph, then converting it to a CMYK TIF/TIFF (with HUGE filesize) before placing it in InDesign, and maybe converting it back to RGB for screen-use? I mean, the photograph is RGB anyway, and InDesign can use colour profiles too. So, if InDesign is assigned the correct profile (from the printing press) why convert the images to CMYK beforehand? Wouldn't it be a much wiser choice to save the retouched images as PNG (which is lossless)? The print designer would then place the image in InDesign and then, when the document is done, export to CMYK using the correct profile. Whereas the web designer would take the image, resize it into the correct format and save it as a JPG.

Advantages:

• Immensely reduced file sizes


• One conversion less


• On-screen viewing can be done by anyone without them getting off colours because their viewer doesn't support CMYK


• 8-bit transparency

Also, I'm not entirely sure if our design agency actually uses the press profile our printers use because the agency is in a completely different country.

Am I missing something crucial here?

Answer

No, you aren't missing something. There is no point at all in converting images to CMYK, and several good reasons NOT to. Converting images to flattened CMYK tiff is an old QuarkXpress workflow that is a complete waste of time today, especially with InDesign.

What is a good idea is to size images in Photoshop before final output, to reduce file size and for maximum control.

If you are placing CMYK images, be certain that InDesign preferences are set so embedded color profiles are retained, otherwise you can get undesirable color shifts on PDF export. Indesign handles conversion to the destination color space at export.