Tk Source Code

When you want to create a black and white photo using the -palette 2 option, you got a corrupted image.

But -palette 1 and -palette 3 work for windows and -palette 2 works for linux.

Backported to core-9-0-branch and core-8-6-branch by commits [9572dd82] and [697d9c36]. Closing the ticket.

Fixed in [710caca0d3] (main), with test imgPhInstance-7.3.

Added test imgPhInstance-7.3 to the branch win-mono-image. It checks the pixels of -palette 2 images with testpixel. It fails on Windows without the fix and passes with it.

Still reproducible on Windows with 8.6 and 9.0, for widths 1-16, 33-48, 65-80, etc. There are two bugs:

• TkAlignImageData() computed the line length of the word-aligned bitmap passed to CreateBitmap() from the line length of the photo data, which is padded to 4 bytes, instead of from the width, so the lines were shifted.
• Windows draws the 1 bits of a monochrome bitmap with the background color, while X draws them with the foreground color, so black and white were swapped for all widths.

Proposed fix in branch win-mono-image, with tests imgPhoto-26.*. With it the images are the same as on Linux, pixel for pixel. A test for the colors with testpixel on 9.1 needs the fix for [32f2e19de8] (branch win-photo-gamma-palette) first, since -palette is ignored there on Windows.

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Using the test script bellow with tclkit 8.4.2 this bug remain for 
*some* images I tried.
Alas, I can't stat why it works for one and it 
doesn't for another.

# Start of Tk test script
# Choose 
small images if you want the display
# part (120 square pixels) 
been representative.

destroy .c
canvas .c
pack 
.c

set imgname [tk_getOpenFile -filetypes [list "{Images} 
{*.gif *.ppm *.pgm}"]]

# Full color test :
image create 
photo TF -file $imgname

# Palette 2 test :
image create 
photo T2 -file $imgname -palette 2

# Palette 16 test :
image 
create photo T3 -file $imgname -palette 16
update 
idletasks
set h2 [image height TF]
if {$h2 > 120} {
    set h2 
120
}
set h3 [expr $h2 * 2]
set hc [expr $h2 * 3]

.c 
configure -height $hc -width 120
wm geometry . 
120x$hc
update

# Display result :
.c create image 0 0 -
anchor nw -image TF
.c create rectangle 30 5 90 20 -width 0 -fill 
yellow
.c create text 60 5 -anchor n -text "Full colors" -fill red
.c 
create image 0 $h2 -anchor nw -image T2
.c create rectangle 30 
[expr $h2+5] 90 [expr $h2+20] -width 0 -fill yellow
.c create text 60 
[expr $h2+5] -anchor n -text "2 colors" -fill red
.c create image 0 $h3 -
anchor nw -image T3
.c create rectangle 30 [expr $h3+5] 90 [expr 
$h3+20] -width 0 -fill yellow
.c create text 60 [expr $h3+5] -anchor n -
text "16 colors" -fill red

# End of test script

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I believe Chengye commited the fix to the head on 03-26 and 
just forgot to close this.

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This is a Tk Windows problem and has been there since 
tk80.  This is a change made in XCreateImage in 
tkWinImage.c.  The line in the function XCreateImage

imagePtr->bitmap_bit_order = MSBFirst; // line 224 ?

specifies the bit order of MSBFirst, which results in 
bigEndian format in bit packing of tkImgPhoto.  I don't 
know the reason for this change, but believe it is a 
problem for the option -palette 2.  The fix is 

imagePtr->bitmap_bit_order = LSBFirst;


Chengye Mao

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I know *nothing* about this. Jeff, perhaps you could pass it
on to someone who actually understands the fault...