bug#39736: 27.0.60; wrong display of scaled checkerd pattern image

[ynyaaa@gmail.com]

A scaled checkered pattern image is converted into a solid gray image.
I expect a large chechered pattern.
Evaluating the form below, a solid gray square is displayed.

(let ((data "\
P1
8 8
01010101
10101010
01010101
10101010
01010101
10101010
01010101
10101010
"))
  (insert-image (create-image data 'pbm t :scale 8)))

The form below temporally displays another image.
The upper side is gray, the lower-left corner is black,
and the lower-right corner is white.
Once the text cursor gets on the image, the whole image is displayed as
a gray square.

(let ((data "P1\n2 2\n01\n10")
      (buf (generate-new-buffer "tmp")))
  (switch-to-buffer buf)
  (insert "\na")
  (goto-char (point-min))
  (redisplay)
  (insert-image (create-image data 'pbm t :scale 16)))


In GNU Emacs 27.0.60 (build 1, x86_64-w64-mingw32)
 of 2019-12-29 built on CIRROCUMULUS
Repository revision: 21c3020fcec0a32122d2680a391864a75393031b
Repository branch: emacs-27
Windowing system distributor 'Microsoft Corp.', version 10.0.18363
System Description: Microsoft Windows 10 Pro (v10.0.1909.18363.657)

Recent messages:

Configured using:
 'configure --without-dbus --host=x86_64-w64-mingw32
 --without-compress-install -C 'CFLAGS=-O2 -static -g3''

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND NOTIFY W32NOTIFY ACL GNUTLS LIBXML2
HARFBUZZ ZLIB TOOLKIT_SCROLL_BARS MODULES THREADS PDUMPER LCMS2 GMP

Important settings:
  value of $LANG: JPN
  locale-coding-system: cp932

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(thingatpt xref project ring gnutls network-stream nsm mailalias
smtpmail auth-source cl-seq eieio eieio-core cl-macs eieio-loaddefs json
map cl-extra misearch multi-isearch pp shadow sort mail-extr emacsbug
message rmc puny dired dired-loaddefs format-spec rfc822 mml mml-sec
password-cache epa derived epg epg-config gnus-util rmail rmail-loaddefs
text-property-search time-date subr-x seq byte-opt gv bytecomp
byte-compile cconv mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums
mm-util mail-prsvr mail-utils term/bobcat help-fns radix-tree cl-print
debug backtrace help-mode easymenu find-func cl-loaddefs cl-lib
japan-util tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel dos-w32 ls-lisp disp-table term/w32-win w32-win
w32-vars term/common-win tool-bar dnd fontset image regexp-opt fringe
tabulated-list replace newcomment text-mode elisp-mode lisp-mode
prog-mode register page tab-bar menu-bar rfn-eshadow isearch timer
select scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame minibuffer cl-generic cham georgian utf-8-lang
misc-lang vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms
cp51932 hebrew greek romanian slovak czech european ethiopic indian
cyrillic chinese composite charscript charprop case-table epa-hook
jka-cmpr-hook help simple abbrev obarray cl-preloaded nadvice loaddefs
button faces cus-face macroexp files text-properties overlay sha1 md5
base64 format env code-pages mule custom widget hashtable-print-readable
backquote threads w32notify w32 lcms2 multi-tty make-network-process
emacs)

Memory information:
((conses 16 69135 12815)
 (symbols 48 7851 5)
 (strings 32 22941 1828)
 (string-bytes 1 729921)
 (vectors 16 15072)
 (vector-slots 8 259276 24684)
 (floats 8 37 321)
 (intervals 56 709 0)
 (buffers 1000 18))