http://imagej.273.s1.nabble.com/Float-floatToIntBits-decrements-in-byte-values-tp3686270p3686273.html
int or long will result in values between -128 and +127. That's
because Java has only signed byte data. There is no unsigned byte (or
Actually, for the last one you could omit the '&0xff'. Shifting by 24
> Thanks your responses,
>
> Apologies for not including useful code in my original posting, I
> was afraid of creating a monster. The code I use for reading the
> floats was just copied and pasted from ij.plugin.DICOM:
>
> /*------------------Snip--------------------------------------
> float getFloat() throws IOException {
> int b0 = getByte();
> int b1 = getByte();
> int b2 = getByte();
> int b3 = getByte();
> int res = 0;
> if (littleEndian) {
> res += b0;
> res += (((long) b1) << 8);
> res += (((long) b2) << 16);
> res += (((long) b3) << 24);
> } else {
> res += b3;
> res += (((long) b2) << 8);
> res += (((long) b1) << 16);
> res += (((long) b0) << 24);
> }
> return Float.intBitsToFloat(res);
> }
> ------------------Snip--------------------------------------*/
>
> For writiing floats into the header I've used a minor variation on
> that in ij.io.ImageWriter. Here "loc" is the location in the header
> block I'm pointing to and imHdr is the header proper.
>
> /*------------------Snip--------------------------------------
> private byte[] imHdr = new byte[2048];
>
> // -------snip--------
>
> void floatToHeader(float m_float, int loc) {
> intToHeader(Float.floatToIntBits(m_float), loc);
> }
>
> void intToHeader(int v, int loc) {
> if (littleEndian) {
> imHdr[loc] = (byte) (v & 255);
> imHdr[loc + 1] = (byte) ((v >>> 8) & 255);
> imHdr[loc + 2] = (byte) ((v >>> 16) & 255);
> imHdr[loc + 3] = (byte) ((v >>> 24) & 255);
> } else {
> imHdr[loc] = (byte) ((v >>> 24) & 255);
> imHdr[loc + 1] = (byte) ((v >>> 16) & 255);
> imHdr[loc + 2] = (byte) ((v >>> 8) & 255);
> imHdr[loc + 3] = (byte) (v & 255);
> }
> }
> ------------------Snip--------------------------------------*/
>
> I am indeed not including &255 when I import the bytes, but without
> a code sample I wouldn't know how to use the logic.
>
> I've tried the above writing operation with (eg) v >>24 instead of
> (v>>>24) & 255 and I get an identical result with the learge
> numbers. I can't remember why I used this variation in the first
> place.
>
> I'm reading in as longs, but I'm not explicitly operating with
> longs when writing - is that a problem?
>
> Does anything smell fishy?
>
> Thanks again, Neil
>
> Neil Thomson,
> Nuclear Medicine Physics Section,
> Medical Physics,
> Kent and Canterbury Hospital,
> UK. CT1 3NG
> +44 (0) 1227 766877
> ________________________________________
> From: ImageJ Interest Group [
[hidden email]] On Behalf Of
> Michael Schmid [
[hidden email]]
> Sent: 06 December 2010 10:28
> To:
[hidden email]
> Subject: Re: Float.floatToIntBits & decrements in byte values
>
> Hi Neil,
>
> maybe you have somewhere forgotten the '&255' on conversion from the
> bytes back to an int? You did not enclose the code for this direction.
>
> Michael
> ________________________________________________________________
>
> On 3 Dec 2010, at 18:24, Thomson Neil (East Kent Hospitals NHS Trust)
> wrote:
>
>> Dear fellow listers
>>
>> I'm writing a plugin to export a medical image format. Some of the
>> header values are floats. The values are in a hash table and I then
>> save the floats into my header-block by doing a
>> Float.floatToIntBits conversion and then save the 4 byte values,
>> which is (more or less) copied and pasted from the IJ tiff encoder.
>>
>> I currently have this code snippet in my format encoder:
>>
>> System.out.println("" + o_value); //o_value is float value of some
>> hashmap entry
>> int v = Float.floatToIntBits((Float) o_value);System.out.println(""
>> + v);
>> System.out.println("" + (byte) ((v >>> 24) & 255));
>> System.out.println("" + (byte) ((v >>> 16) & 255));
>> System.out.println("" + (byte) ((v >>> 8) & 255));
>> System.out.println("" + (byte) (v & 255));
>> When float values of o_value these are small (say 1E5) everything
>> seems fine, but when they get larger (say 1E7) the byte output does
>> not seem to be as I would expect. If I import and then export ann
>> image without manipulation, the float value decreases, which I've
>> traced to the byte values: if I start by importing an image where
>> this particular float header field has bytes reading (in big-
>> endian)...
>>
>> 76,-46,-20,-18
>>
>> ... I then export the image and re-import it I get:
>>
>> 75,-47,-21,-18
>>
>> ... and again...:
>>
>> 74,-48,-22,-18
>>
>> A decrement in three of the four bytes. I'm at a loss as to where
>> to go next and I would greatly appreciate some wise words.
>>
>> Many thanks, Neil
>>
>> Neil Thomson,
>> Nuclear Medicine Physics Section,
>> Medical Physics,
>> Kent and Canterbury Hospital,
>> UK. CT1 3NG
>> +44 (0) 1227 766877
>>
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> the intended recipient please inform the
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> Please do not disclose, copy or distribute information in this e-
> mail or take any action in reliance on its contents:
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> Thank you for your co-operation.
>
> NHSmail is the secure email and directory service available for all
> NHS staff in England and Scotland
> NHSmail is approved for exchanging patient data and other sensitive
> information with NHSmail and GSi recipients
> NHSmail provides an email address for your career in the NHS and
> can be accessed anywhere
> For more information and to find out how you can switch, visit
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