Mitsubishi P91W Instruction Manual download pdf (Page 98)

ChemiDoc MP with Image Lab Software | Analyzing Images

Local—local background subtraction calculates a separate background

intensity for each unknown and standard volume you create. For each volume,

the intensities of the pixels in a 1-pixel border around the volume are added

together and divided by the total number of border pixels. This gives an

average intensity for the background around each, which is then subtracted

from the intensity of each pixel inside the volume. If the background value is

greater than the pixel value inside the volume, the background-adjusted

quantity of the volume may be <0. In this case, redraw the border for this

volume.

Global—global background subtraction calculates a single background

intensity for the entire gel. This average background intensity is then

subtracted from all the volumes in the gel. The average intensity of the pixels

in the background volume is calculated and subtracted from each pixel in all

standard and unknown volumes. Therefore, it is not necessary for the

background volume area to be the same size as your unknown.

To calculate global background subtraction:

1. Use one of the volume tools to create a volume in a representative

background region of your image (that is, a nondata region similar to the

background surrounding your data).

2. Double-click the volume. This opens the Volume Properties dialog box.

3. Select the Background option button.

Notes:

• If you select Global in the Volume toolbox but do not define a

background volume as described, no background subtraction is

performed

• If you create more than one background volume, all the pixels in

those background volumes are used to calculate the average

background. Your background volume(s) will have default names

B1, B2, and so on based on the sequence in which they were

created

• If the region you defined as background has a higher average

intensity value than your data object, you obtain a negative value

for your adjusted volume in the analysis table. If this happens,

select a new background region with less intensity than your data

object

RELATIVE VOLUME QUANTITY

You can choose any one volume as a Reference Volume by selecting the

Reference Volume checkbox in the Volume Properties dialog box. The

Reference Volume is indicated by an asterisk on the volume label, for

example, U1*.

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Mitsubishi P91W Instruction Manual Page 98