1024 grayscale

[MulchDiggums]

Hi everyone,

I just started doing my phd. I will train people in a visual task. Therefore, I need to draw stimuli with low contrast to stimulate the participants. As my standard 24-Bit RGB stimuli aren't satisfying, my second supervisor told me to use 1024 grayscale. As I'm a absolutel newbie to that stuff, I tried different editing software (PaintShop Photo, Photo-Paint, CorelDRAW and also gimp). I can only change between 8- and 16 Bit grayscale respectively 24/48 Bit RGB or CMYK. However, as soon as I try to change the contrast (i.e. by the use of the histrogram), I only have 256 grayscale values.
Is there anyone out there who can tell me how that works? I'm already going mad

I hope I post this in the right forum. If not, please tell me where I should post it.
Thanks a lot.

[teknisyan]

I'm sure if you need to do this via software, it looks like 1024 grayscale is more of a monitor or display settings.

[df]

There are tools that will work with 16 bit images and tools that work with 8 bit images. If you're trying to use a true grayscale image though you can't get that much information in a 16 bit image. If I start with a grayscale image I can increase the color depth to 16 bit, but then it's not a "grayscale" anymore. I can also take a 16 bit image and convert it to grayscale, but then it's not 16 bit anymore. I've also tried this in Photoshop Elements 9.0 and got the same results.

At any rate, you can take a grayscale image and increase the color depth. Image> Increase Color Depth> RGB 16 bits per channel.
Then you can use other tools that do not reset the color depth. In PSP X4 that's things like Brightness Contrast, Curves, Levels, just to name a few. It helps if you make sure the program doesn't just convert 16 to 8 bit automatically when an unsupported tool is selected. Click File> Preferences> General Program Preferences. Select the Auto Action tab on the left, click Prompt All> OK. Now the program will always ask if you want to convert to 8 bit or stay in 16 (unless you're manually changing the file type to 8 bit or grayscale). It will also prompt you with most anything else, but you will have the option to check whether to always prompt or just go ahead and you can figure it out from there.

At any rate, you should likely verify with your supervisor what they mean as this is not a true grayscale image but rather an RGB image that appears grayscale.

[hartpaul]

As suggested you should check with your supervisor what they mean by 1024 greyscale.
I did a search for 1024 greyscale and after your post was brought up the only hit was this :

http://forums.codeguru.com/showthread.php?t=311557

If my understanding of jpgs is correct then you could not have a jpg with 1024 shades of grey.
A jpg consists of a red blue and green channel with values from 0 to 255.
So in order RGB
Black is 0,0,0 while white is 255,255,255

Various greys are produced by equal amounts of the three colours. eg 128,128,128. 128,128,129 would be a grey with very slight blue cast to it having a bit more blue in it. This would be imperceptable to the human eye as we can only detect from 7 million to 10 million of the 16 million available shades of a jpg pixel. In practise I have found that for me there has to be a change in at least 3 units for me to be able to detect a difference. eg 128,128, 129 : 128,128,130: 128, 128, 131 would appear the same to my eyes.

[MulchDiggums]

Thanks a lot for your quick replies.
It obviously worked with PSP, now. As the histrogram function doesn't work with 16 Bit/channel, I have to use the Brightness/Contrast function and a gauss filter to further lower the contrast.
As my hardware cannot display more the 32 bite colour, I have to find a newer machine, now. It seems that I need a graphic adapter with hdmi.
I'll keep you informed if that works.