Converting to 16/256 colors?

I have some scans of nautical charts (like maps) that I want to input to another program to calibrate them. The help file for this program says: "Most maps and charts are about 12 colors or less, so they should be reduced to 16 colors ... Charts and maps should be 16 color, because they get their clarity from block colors like a cartoon".

If I just change the Image|Mode to 16 (or 256) colors, it looks terrible. Areas around text become jagged, and some colors that should be uniform become dithered. Ideally, I'd like a way to map certain ranges of color to a solid color - I guess an interactive posterize?

What is the best way to do this in CS3?

On Thu, 01 Nov 2007 17:49:22 +0000, Nigel Molesworth
wrote:

I have some scans of nautical charts

Here's an example of a section of one.

< http://i77.photobucket.com/albums/j54/nigelmercier/Misc/5767 -1.jpg>

"Nigel Molesworth" wrote in message

I have some scans of nautical charts (like maps) that I want to input to another program to calibrate them. The help file for this program says: "Most maps and charts are about 12 colors or less, so they should be reduced
to 16 colors ... Charts and maps should be 16 color, because they get their
clarity from block colors like a cartoon".

If I just change the Image|Mode to 16 (or 256) colors, it looks terrible. Areas around text become jagged, and some colors that should be uniform become dithered. Ideally, I'd like a way to map certain ranges of color to a
solid color - I guess an interactive posterize?

What is the best way to do this in CS3?

They usually start with much larger pictures, change colors to 16 colors (that's index mode), and make a custom color table (also under mode) with what they wish. Are you certain they are asking for 16 bit depth? I rather think they mean 16 colors, not bits.

"Nigel Molesworth" wrote in message

On Thu, 01 Nov 2007 17:49:22 +0000, Nigel Molesworth
wrote:

I have some scans of nautical charts

Here's an example of a section of one.

< http://i77.photobucket.com/albums/j54/nigelmercier/Misc/5767 -1.jpg>

Open the RGB image.
Under MODE, switch mode to 8-bit/channel.
Under MODE switch to INDEX color. At the top of the dialog is a drop-down menu for Palette: Choose CUSTOM.
The palette will open and show you the existing colors.
Stick to those (or replace any one by clicking on it.)
Be happy.

Hope this helps.

Nigel Molesworth wrote:

On Thu, 01 Nov 2007 17:49:22 +0000, Nigel Molesworth
wrote:

I have some scans of nautical charts

Here's an example of a section of one.

< http://i77.photobucket.com/albums/j54/nigelmercier/Misc/5767 -1.jpg>

Convert to Index Mode and save as GIF, and you can reduce to around 8 colors which often more than enough for MAP, and the size will even smaller than 16-colors.

... and I wonder if you will read and response to the replies?

"pico" <pico.pico.pico> wrote in message

"Nigel Molesworth" wrote in message

I have some scans of nautical charts (like maps) that I want to input to another program to calibrate them. The help file for this program says: "Most maps and charts are about 12 colors or less, so they should be reduced
to 16 colors ... Charts and maps should be 16 color, because they get their
clarity from block colors like a cartoon".

If I just change the Image|Mode to 16 (or 256) colors, it looks terrible. Areas around text become jagged, and some colors that should be uniform become dithered. Ideally, I'd like a way to map certain ranges of color to a
solid color - I guess an interactive posterize?

What is the best way to do this in CS3?

They usually start with much larger pictures, change colors to 16 colors (that's index mode), and make a custom color table (also under mode) with what they wish. Are you certain they are asking for 16 bit depth? I rather think they mean 16 colors, not bits.

It only has 6 colors anyway??
light blue- dark blue- yellow- black and white?

On Sat, 03 Nov 2007 10:54:47 -0500, Joe wrote:

Convert to Index Mode and save as GIF

Thanks for the ideas. The problem I was having was that there was a lot of colour noise, but I think I've cracked it by using Smart Blur.

Nigel Molesworth wrote:

On Sat, 03 Nov 2007 10:54:47 -0500, Joe wrote:

Convert to Index Mode and save as GIF

Thanks for the ideas. The problem I was having was that there was a lot of colour noise, but I think I've cracked it by using Smart Blur.

It depends on the original image, some GIF looks good with 16 colors, some has to be 60-100+ colors to look ok. The sad thing that 256 color GIF often lot larger than 16+mil color of JPG with good compression.

Nigel Molesworth wrote:

On Sat, 03 Nov 2007 10:54:47 -0500, Joe wrote:

Convert to Index Mode and save as GIF

Thanks for the ideas. The problem I was having was that there was a lot of colour noise, but I think I've cracked it by using Smart Blur.

Oops! I don't remember what the original message was about, but if you are talking about Animated GIF then there is a trick to reduce the size to minimal. By follwing these steps.

1. Have the FULL original and use as background (base)

2. For the animating frames DO NOT use the full size *but* only the area you want to animated.

Example you have a portrait of a person and you want to animate the EYES and MOUTH. Then you replacve the eyes and mouth areas with the tiny images of the eyes and mouth.

And you will need some tool like Ulead GIF Animate or similar, as Ulead GIF Animator was the one I used when making animated GIF for web page.

Nigel Molesworth wrote:

Thanks for the ideas. The problem I was having was that there was a lot of colour noise, but I think I've cracked it by using Smart Blur.

Good work. Sometimes it helps to do Surface Blur then Cut-Out with slightly lower edge fidelity (detail) and finnesse with curves. It truly depends upon the original.