Wednesday, December 31, 2008

Color to Grayscale bug in Photoshop CS

I noticed a weird bug in ALL the CS versions of Photoshop, both on PC and Mac. I Googled it and didn't find any mention of it. It affects all files in RGB or CMYK converted to Grayscale.

Let's say you have a RGB or CMYK image that contains flat colors (that means no gradients or anti-alias) and decide to convert it to Grayscale to eventually convert it to Screen-tones Bitmap (you can't go directly from color to bitmap). On the left: a flat 50% black in a RGB file. On the right, the same, but converted to Grayscale. Notice anything on the Grayscale image? Depending on your screen's calibration, you might not. But if you use the magic wand to select the color, which since it's flat should select the entire image, you notice something.

The color isn't flat anymore! The 50% Black image is now sprinkled with 49% Black pixels (I've zoomed on the image). Now that might seem like nothing, especialy on the web. But if you print it in screen-tones, it suddenly becomes apparent.
Noticed all those checkered spots? I didn't exagerate them on the scan, they are clearly visible on the print. It's ugly as shit and looks unprofessional. This bug only exists on the CS version of Photoshop. Version 5.5 does not have this problem. Me and my graphic designer friends (people who work in print and know their way around this stuff) tried a lot of potential solutions and couldn't fix it (color management, etc).

The only way I found to fix it is to do the color to grayscale conversion in a free image editing / image viewer program (Irfanview), save it and open it in Photoshop. If the conversion is done outside of Photoshop, the problem is gone. But considering Adobe Photoshop CS is a high end professional application, it's a bit damning that you need a freeware to complete the job properly.

So on my side, I consider this bug fixed. But I would suggest Adobe get their act together, because this kind of crap is unacceptable.

13 Comments:

Anonymous Anonymous said...

whenever I need to convert files to greyscale or from one format to another, I use a free program called "IrfanView". Some of the "adjustments" settings are not under what you would expect them to be, but I'm happy with all of the file conversions and greyscales I have done.(but I should mention that I'm not an artist and am easily pleased.) It also does batch conversions of files, as well as slideshows, etc.

CV

6:35 PM  
Blogger Kai v3.0 said...

When all else fails, use fire.

6:51 PM  
Anonymous Anonymous said...

Heh, that 49% is probably something like dithering. I guess they decided to add dithering to the greyscale conversion to try to add more accuracy, but that has its downsides.

7:47 PM  
Blogger Sirkowski said...

Yeah, if it's indeed dithering, it's extremely retarded.

7:49 PM  
Anonymous MossMan said...

My only problem with Irfanview - ever since the beginning in fact - has been a problem that you may also encounter in this situation!

Namely; when you alter the colours, specifically when reducing the number of them, it screws around with the palette! For example, take a 24-bit colour image which only has four unique colours in it - now reduce the number of colours to four (or sixteen, or whatever) and you'll find black has turned to 3,3,3 while white has become 252,252,252 etc.

It's a PITA since I often want to copy graphs and line drawings from various sources and put them in reports - Irfanview is a perfect way to take a big ol' bitmap and make a tiny little PNG... but I often curse when I print the thing and find huge areas of fuzzy grey instead of white.

That means I always have to reduce the number of colours and then correct the palette by hand.

I even mailed Irfan a while back but he didn't see any urgency in fixing it.

11:34 PM  
Anonymous Darlo said...

Did you mail Adobe about this bug? If it's not on the web and they don't know about it (which sounds odd now that I've wrote that), they might ask you to help them with it.

10:35 AM  
Anonymous Anonymous said...

Like Microsoft and it's crashing Zunes, they are the 800lb gorilla on Viagra and can do what they want...

Sooner or later, user-made free ware like Gimp will catch up, then they'll probably sue to keep it down.

2:51 PM  
Blogger Sirkowski said...

Who knows, Gimp might already work better. I'll have to try it someday.

3:17 PM  
Anonymous Anonymous said...

I've been impressed with the latest GIMP, altho I lack the skills to really give a meaningful opinion of it. Still, since it's very similar to Photoshop in it's operation, the learning curve should be small if you were to give it a try.

6:16 PM  
Blogger Daniel said...

While GIMP is a great program (this is yet another unprofessional opinion), it seems to have a problem with crashing on Windows. Personally, I haven't had this problem on Ubuntu or running GIMP from a flash drive when I do use Windows, but I have a friend who has had the program crash on him during certain file conversions. Of course, it has been awhile since I talked to him about it, last I checked he still uses it, and for all I know this bug has probably been resolved, but I thought you might like a word of warning. It's still a pretty badass program, since it has so many interesting little effects. If you do decide to try it, you might want to look into getting the add-on, GIMPshop, which arranges the GIMP interface like Photoshop's - it might make the transition easier.

11:11 PM  
Blogger Sirkowski said...

I've also heard about GIMP crashing on Windows, but it was years ago as well.

12:05 AM  
Anonymous Anonymous said...

Confirmed that I can't replicate problem on 4, 5, or PS 7

Gimp is... odd to get used to at first. It's familiar, and at the same time... not. And admittedly I am NOT a photoshop power user, so your mileage may vary, but so far I've been able to everything on Gimp that I could in PS. I've stuck with PS simply out of habit though.

9:05 AM  
Anonymous Seamus said...

I didn't believe this until I tried it myself. Image > Mode > 16 Bits/Channel then Image > Mode > Greyscale seems to work.

4:55 PM  

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