Re: Adjusting contrast levels for a batch of TIFF files

Posted by Harry Parker on May 20, 2008; 2:46pm
URL: http://imagej.273.s1.nabble.com/Adjusting-contrast-levels-for-a-batch-of-TIFF-files-tp3696177p3696178.html

Hi Venu,

I am not sure of what you want to do. One thing I've noticed for 16 bit images is that Photoshop expects white to be 2^16 - 1 = 65535 , while ImageJ looks at the distribution of values and displays the darkest as black and the lightest as white automatically. I'm assuming you have a similar problem.

I had 10 bit linear images (max = 2^10-1=1023) saved in 16 bit format. They looked good in ImageJ but black in Photoshop until I manually changed the contrast. By multiplying all the values in my images by 64, they looked good when opened in Photoshop. This is a single command in ImageJ ( menu: Process->Math->Multiply...->[type] 64.)
Its very easy to apply the same processing to a whole folder of images. See the ImageJ documentation on "Virtual Stacks", or the example macros starting with "batch".

If your images are linear in intensity, you will also want to adjust their "gamma" by some number around 0.5 to brighten the middle gray values. (0.4545 is the standard value.) (Menu: Process->Math->Gamma...) This is required to compensate for the nonlinear intensity characteristics of computer displays. You may also want to first subtract some value from all your pixels if your darkest pixels look too light.
 
--
Harry Parker
Senior Systems Engineer
Digital Imaging Systems, Inc.


----- Original Message ----
From: kesireddy venu <[hidden email]>
To: [hidden email]
Sent: Tuesday, May 20, 2008 3:48:21 AM
Subject: Adjusting contrast levels for a batch of TIFF files

Dear list members ,

I am looking for a simple way which can adjust the contrast levels of TIFF files  for a large batch of images.( Save those contast adjusted images) Opening each image and adjusting the contrast levels is very laborious work. Unfortunately other propritery software that I am using takes only contrast adjusted images. While Image J can display images of correct intensity automatically.The software I am using has no such option to adjust contrast levels.
So are there any tricks to change contrast levels for a btach of TIFF files in photoshop or in ImageJ

SINCERELY
VENU