grayscale bmp files

E
Posted By
eventide
May 11, 2004
Views
562
Replies
8
Status
Closed
I can’t seem to save my bmp files in grayscale.
When I reopen them they come in as index color
What am I doing wrong?

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GH
Gernot_Hoffmann
May 11, 2004

E.T.,

Grayscale, directly saved as BMP, is indexed color. Nothing wrong – it´s a file with one byte per pixel. The byte points to a row in a table where all entries RGB are equal.

If you convert first to Grayscale and then to RGB, then you will get BMP-24 with three equal bytes per pixel.
The image is still gray.

This shows once again that "Grayscale" is an ill-defined format.

Best regards –Gernot Hoffmann
MO
Mike_Ornellas
May 11, 2004
If you keep opening, then converting the file to Greyscale, and saving it as a BMP format, you induce rounding errors and basically screw up the file, so don’t convert a BMP to Greyscale, and then save it.

btw, you are actually screwing it up twice when doing this.
E
eventide
May 11, 2004
Actually the image was originally a jpeg that was
resampled and saved as a grayscale bmp. Would it
be better to save it as a tiff?
RW
Rene_Walling
May 11, 2004
I would say yes.
GH
Gernot_Hoffmann
May 11, 2004

E.T.,

if you load a (color) JPEG and convert to Grayscale
and save as BMP (that´s BMP-8 indexed) then it´s the same as saving as TIFF. No information lost. No information
about the original color image in either case.

What´s the purpose of your question ?

The big problems will arise for CMYK grayscale images.

Best regards –Gernot Hoffmann
E
eventide
May 11, 2004
Original photos were rgb jpeg images from a digital camera. These images are to be used in a 1 color newsletter. What would you suggest is the best way to supply these images to the printer?
GH
Gernot_Hoffmann
May 12, 2004

E.T.,

1. Convert RGB JPG to RGB TIFF
2. Convert RGB to Grayscale, save as TIFF
3. Apply image processing (e.g. sharpening, contrast)
4. Send TIFF to printer (if you mean the service provider)

In Color Settings choose Grayscale Gamma=2.2.
If you want to provide CMYK K-only images then it is more difficult.

I´m recommending TIFF. BMP is not wrong, but the prepress folks expect TIFF because they often think that BMP is
unreliable.

Best regards –Gernot Hoffmann
E
eventide
May 12, 2004
That’s what I thought. We have never had a problem before until we noticed that the grayscale images for some reason remained index color. Thanks for your help, at least I know there never really was a problem!

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