Arcane Question on Color Tables

J
Posted By
Jim
Sep 30, 2004
Views
301
Replies
2
Status
Closed
Hi All,

Any ideas on the following using Windows and PS7.

1) Open an image

2) Image > Mode > Indexed Color

3) Image > Mode > Color Table: Save the table as test.act

4) Alt-PrintScreen to capture the Color Table menu.

5) File > New and paste in the clipboard so that now the Color Table menu is an image file.

6) With a binary file editor, open the file test.act and read off the first few values.

7) Using the Info Palette, put your mouse cursor over the table cells that correspond to the cells read from the previous step and note that values.

Here is what I got.

Color Table RGB Value RGB value in Info palette
5,254,255 8, 255, 255 and 0,247,255 22,251,255 24,247,255 and 16,247,255 19.248,255 16,247,255
8,248,255 8,247,255

Now my question is why the discrepancy between the RGB values in the color table and the values as picked up in the screen capture of the color table graphic?

Any ideas?

Thanks.

Best Regards, Jim Plaxco
National Space Society http://www.nss.org
Astrodigital http://www.astrodigital.org

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MR
Mike Russell
Sep 30, 2004
Jim wrote:
Hi All,

Any ideas on the following using Windows and PS7.

1) Open an image

2) Image > Mode > Indexed Color

3) Image > Mode > Color Table: Save the table as test.act
4) Alt-PrintScreen to capture the Color Table menu.

5) File > New and paste in the clipboard so that now the Color Table menu is an image file.

6) With a binary file editor, open the file test.act and read off the first few values.

7) Using the Info Palette, put your mouse cursor over the table cells that correspond to the cells read from the previous step and note that values.

Here is what I got.

Color Table RGB Value RGB value in Info palette
5,254,255 8, 255, 255 and 0,247,255 22,251,255 24,247,255 and 16,247,255 19.248,255 16,247,255
8,248,255 8,247,255

Now my question is why the discrepancy between the RGB values in the color table and the values as picked up in the screen capture of the color table graphic?

Any ideas?

Photoshop uses your monitor’s display profile to convert RGB values from your working space to your monitor space. If you set your working space to your monitor profile, the numbers will match.

If you like this kind of puzzle, here’a another one. Create two images, and assign one of the image’s profile to Wide Gamut RGB. Now use the paint brush to paint any of the pure RGB colors (red, yellow, green, etc) in the Swatches palette. Use the info palette to verify that these colors are painted as advertised.

Now pick a color from the second or third rows of the Swatches, for example the Pastel Red which is leftmost in the third row. When you paint that color, notice that the RGB values are now different in the two images.

Can you explain why the colors are different for Pastel Red, but not the colors from the top row?


Mike Russell
www.curvemeister.com
www.geigy.2y.net
J
Jim
Oct 1, 2004
Hi Mike,

On Thu, 30 Sep 2004 06:33:57 GMT, "Mike Russell" wrote:

Jim wrote:
Hi All,

Any ideas on the following using Windows and PS7.

1) Open an image

2) Image > Mode > Indexed Color

3) Image > Mode > Color Table: Save the table as test.act
4) Alt-PrintScreen to capture the Color Table menu.

5) File > New and paste in the clipboard so that now the Color Table menu is an image file.

6) With a binary file editor, open the file test.act and read off the first few values.

7) Using the Info Palette, put your mouse cursor over the table cells that correspond to the cells read from the previous step and note that values.

Here is what I got.

Color Table RGB Value RGB value in Info palette
5,254,255 8, 255, 255 and 0,247,255 22,251,255 24,247,255 and 16,247,255 19.248,255 16,247,255
8,248,255 8,247,255

Now my question is why the discrepancy between the RGB values in the color table and the values as picked up in the screen capture of the color table graphic?

Any ideas?

Photoshop uses your monitor’s display profile to convert RGB values from your working space to your monitor space. If you set your working space to your monitor profile, the numbers will match.

That never occurred to me. Thank you for this insight. Alas, with Photoshop it seems that there is always something new to learn.

If you like this kind of puzzle,

Actually, no! I don’t even know what possessed me to go through the above procedure. This all came about because I was investigating creating my own color tables programmatically.

here’a another one. Create two images, and
assign one of the image’s profile to Wide Gamut RGB. Now use the paint brush to paint any of the pure RGB colors (red, yellow, green, etc) in the Swatches palette. Use the info palette to verify that these colors are painted as advertised.

Now pick a color from the second or third rows of the Swatches, for example the Pastel Red which is leftmost in the third row. When you paint that color, notice that the RGB values are now different in the two images.
Can you explain why the colors are different for Pastel Red, but not the colors from the top row?

Not a chance. Perhaps it has something to do with the wishy-washy nature of pastels,

Thanks again Mike.

Best Regards, Jim Plaxco
National Space Society http://www.nss.org
Astrodigital http://www.astrodigital.org

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