comp.lang.idl-pvwave archive: archive » Re: Conversion floating point to byte or integer

Home » Public Forums » archive » Re: Conversion floating point to byte or integer

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: Conversion floating point to byte or integer [message #56321 is a reply to message #56320]

Wed, 10 October 2007 23:08

Jean H.
Messages: 472
Registered: July 2006

Senior Member

>> So what do you want to do with values greater than 255?
>>
>> You could do
>> 1) compute your new image as a float,
>> 2) scale everything down so ALL of your values are between 0 and 255 and
>> save the image
>> or 2) brightPixels = where(image gt 255)
>> image[brightPixels] = 255 and save the image
>
> Jean,
>
> Thank you for your prompt reply and 2) is what I wanted.
> Could I ask why this happen? Am I asking too basic question about
> programming?

So you need to scale it, not to typecast it.
In IDL, if you typecast to byte, it does "wrap around" values, so that
255 is followed by 0...
IDL> print, byte(256)
0
IDL> print, byte(256+257)
1

if you scale it using BytScl(), it takes the smallest value and assign
it to 0, the max value to 255, and the result is a byte array
IDL> print, bytscl([250,251])
0 255

Jean

> I casted output format to bytarr(cols, rows) to scale everything down
> 0-255, but result was same.
> I've read variables part in Liam's book, and tried the least
> significant 8 bit extraction.
> That doesn't seem to be the answer.
>
> Well, thank you again.
> Kim
>

Report message to a moderator

[Message index]

		Re: Conversion floating point to byte or integer By: beardown911 on Thu, 11 October 2007 18:44
		Re: Conversion floating point to byte or integer By: M. Katz on Thu, 11 October 2007 14:04
		Re: Conversion floating point to byte or integer By: beardown911 on Thu, 11 October 2007 06:22
		Re: Conversion floating point to byte or integer By: beardown911 on Thu, 11 October 2007 06:20
		Re: Conversion floating point to byte or integer By: Maarten[1] on Thu, 11 October 2007 01:05
		Re: Conversion floating point to byte or integer By: Jean H. on Wed, 10 October 2007 23:08
		Re: Conversion floating point to byte or integer By: beardown911 on Wed, 10 October 2007 21:20
		Re: Conversion floating point to byte or integer By: Jean H. on Wed, 10 October 2007 16:44

Previous Topic:	Re: Minor IDL code changes cause large slowdowns elsewhere in code
Next Topic:	Re: Problem while deleting shape file

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Sun Oct 12 00:03:47 PDT 2025

Total time taken to generate the page: 0.24023 seconds