If you play a track with gallery, "Gallery, Gallery (2), Gallery (3)" will be unlocked when 1/3/5 numbers of charts are cleared repectively. Most of "Gallery (4) or more" are unlocked by achievements. EXTRA galleries (1) to (7) are not bound with a song and all will be unlocked by achievements.

From May 28, 2020 with Clazziquai and Black Square DLCs, galleries are now unlocked by just successfully finishing the eligible tracks 1/3/5 times, simply play count 1/3/5. I don't know this applied to the main game, V Extension, and Trilogy DLC's galleries retroactively.

갤러리, 갤러리 (2), 갤러리 (3)은 각각 해당 곡의 보면(패턴) 종류를 1/3/5가지 깨면 얻을 수 있습니다. 갤러리 (4)부터는 거의 다 업적으로 해금되는 갤러리이며 EXTRA 갤러리 (1)부터 (7)은 모두 업적으로 해금됩니다.

2020. 5. 28일자 클래지콰이/블랙 스퀘어 디엘시부터 갤러리 해금 조건이 해당 곡의 1/3/5가지 패턴 클리어가 아니라 그냥 클리어 횟수 1/3/5번으로 바뀌었습니다. 본판/브이 확장팩/트릴로지 디엘시의 갤러리에도 소급 적용됐는지는 모르겠습니다.

https://docs.google.com/spreadsheets/d/e/2PACX-1vThrrTCLVOASqQvGUHqDgTiLB5xEqPItqe16nCEUu9IItXWolFwdIiAPM_copGEA2v-jL-e9iS9F15L/pubhtml?gid=0&single=true

• The first column in English: Source / Song name / # of needed play counts to unlock all gallery items / Gallery / Gallery (2) / Gallery (3) / Gallery (4) / Gallery (5) / Gallery (6) / Gallery (7) / Sum / Update date
  
• The order is same as the in-game galleries order.
  
• Cells in yellow mean unlocked by achievements.
  
• Cells in sky-blue are unusual:
  • "Lift You Up Gallery (4)" is unlocked by completing "Respect Mission 1-3 Day Dream".
    
  • "DJMAX RESPECT U Gallery" is unlocked by completing "Trilogy Mission 1-6 DJMAX RESPECT U".
    
  • "DJMAX RESPECT U Gallery (2)" is unlocked by competing "Trilogy Mission 2-5 Boss Match".
    
  • "Lover" and "Y"'s galleries are unlocked ONLY by playing "CE Style", not "BS Style".
    
  • "EXTRA (8)" gallery is unlocked by completing "Clazziquai Mission 1-6 CLAZZIQUAI".
    
  • "Clear (Flea Ver.)" gallery is unlocked by playing "Flea" 1 time.
    
  • "Fail (Flea Ver.)" gallery is unlocked by playing "Flea" 3 times.
    
  • "Heart of Witch", "Rage Of Demon", "Xeus", "Dream it", and "Lost Serenity" need to be played 7 times to unlock their galleries fully upto Gallery (5), not like usual 5 play counts.
    
  • "EXTRA (9)" gallery is unlocked by completing "Technika 1 Mission 1-6 Eclipse".
    
  • "EXTRA (10)" gallery is unlocked by completing "Technika 1 Mission 2-5 Customizer".
    
  • "EXTRA (11)" gallery is unlocked by completing "Black Square Mission 2-5 BS 24".