Printing RGB photos on CMYK printer

[JLD984]

Hi all, I'm wondering the best way to go about printing photos on a Roland (SP540V) printer, seeing photos are usually RGB. I've been opening them in Illustrator and changing it to CMYK before doing anything else. Does this sound right or should I be leaving them as RGB? Any help appreciated. Any tips for printing onto canvas would be great too.

 

[Salmoneye]

We leave ours as RGB and save as EPS

 

[FrankW]

There is no need to convert.

Color Space of print documents will be converted to the Profile Connection Space by the appropriate CMYK- or RGB input profiles (set in the RIP or embedded to the file), no matter if the Photo is RGB or CMYK.

Converting images from RGB to CMYK could be negative because it could lead to a reduction of the color space.

 

[JLD984]

Thanks, I'll have to get out of that habit then. I'm used to mainly doing vector artwork for signs and know the CMYK values of a lot of colours off by heart, but these values change when pasting into a RGB file so I've preferred to convert it.

 

[MikeD]

The conversion to CMYK from RGB is usually handled by the RIP

 

[synergy_jim]

roland's rip prints wider color gamut when printing from RGB colorspace, so you are fine.

 

[bob]

Your RIP will do a far better job interpreting RGB than any other software you or anyone else has.

Here's why, sort of...

When you convert a bitmap from RGB to CMYK, regardless of what software you might be using, each pixel is mapped from its RGB value to some arbitrary CMYK value. One by one.

When a RIP maps an RGB bitmap ultimately into CMYK for printing AND you're properly printing at a higher printer resolution than the bitmap resolution, at least 4 to 1 being optimum, then [assuming for this exposition a 4:1 printer to bitmap resolution ratio] each bitmap pixel is mapped into 16 printer pixels. A process, referred to as 'dithering', then allocates each of the 16 printer pixels to some CMYK value in an attempt to use those 16 pixels together to better reproduce the original RGB value of the bitmap pixel. A good dithering algorithm with sufficient room can hit colors not normally seen in the CMYK spectrum but common to RGB.

In other words, when you let the RIP deal with it, it has a lot more to work with.

 

[WI]

Regardless of your workflow, you probably want to tell your customers to send you images that have been designed and saved in CMYK. This will likely save you hours and hours of explaining to people why R:0 G:0 B:100 is this mad, intense blue on a monitor but prints navy.

 

[P Wagner]

Oy vey...

 

[bbeens]

Disregard Bob's post. Aside from the first line the rest is complete nonsense. Your rip certainly does not convert RGB into arbitrary CMYK values. FrankW is correct. The negative effect he talks about when converting to CMYK is generally caused by selecting a CMYK colorspace that has a smaller gamut then your Roland's profile. Most default CMYK colorspaces in the US are based on offset devices like SWOP. If you convert the file to CMYK using the output profile of your printer the results should be very close to having the rip do the conversion.

Bryan

 

[bob]

Disregard Bob's post. Aside from the first line the rest is complete nonsense. Your rip certainly does not convert RGB into arbitrary CMYK values. FrankW is correct. The negative effect he talks about when converting to CMYK is generally caused by selecting a CMYK colorspace that has a smaller gamut then your Roland's profile. Most default CMYK colorspaces in the US are based on offset devices like SWOP. If you convert the file to CMYK using the output profile of your printer the results should be very close to having the rip do the conversion.

Bryan

Disregard it at your peril, sport. I was creating dither algorithms when you were making in your pants. I know from whence I speak, unlike the coven of 'convert to CMYK' specimens.

The proof is in the printing. I routinely send RGB bitmaps to my RIP and what comes out of the printer is pretty much what I input. Colors difficult if not impossible to reproduce in a simplistic pixel by pixel RGB to CMYK mapping are produced. Had I converted those bitmaps to CMYK beforehand I would have gotten the typical blue to purple shift and a general muddying of everything.

And the pixel to pixel RGB to CMYK mapping is arbitrary, if it were not arbitrary then all conversions via any mechanism would yield identical results. They do not.

 

[Baz]

I get MUCH better results and far brighter colors when designing in RGB for both vector and bitmap files. CMYK is ugly as hell ...