Image compression automation increasing the file size instead of reducing it.

Question

I’ve built an automation to compress images picked from a Raw Images folder and save them to a Compressed Images folder. The Zap works as expected for images around 200–300 KB but increases file size for images above ~300 KB, even at very low quality settings.

Goal:
Compress images larger than 200 KB to below 200 KB at ~80% quality.

Expected Behavior:
Compressed image size should always be smaller than original.

Actual Behavior:

Images above ~300 KB increase in size after compression
Same issue at 80% and 30% quality
Happens across multiple compression apps

Apps Used:

Trigger: Google Drive
Compression tools tested: Mallabe Images, Picsart
Destination: Compressed Images folder

Compression Settings:

Quality: 80% (default), tested down to 30%
Condition: Only process images >200 KB
Output target: <200 KB

What I’ve Tried:

Multiple compression tools
Lower quality levels
File size filtering
Verified source file sizes

Question:
Why does image compression increase file size for larger images in Zapier, and is there a recommended way to reliably compress images below a fixed size threshold?

I’ve attached screenshots showing original vs compressed file sizes and also a screenshot of the ZAP.

ZAP
Filter step at Step 3
Compression at 30 I have tried 80 before
Original PIC Copy of Lamb Stew Process Photos (9) - 343 Kb
Compressed to 30% - 308 Kb
Compressed at 80% - 442 kb and 544 kb

Troy Tessalone · Answer

Hi ​@AbhiSoodYou are using the wrong Looping variable in Zap step 5.Do NOT usevariables with “Preview”.Help links for using Looping in Zaps:https://zapier.com/apps/looping/integrations#helpWhen you test a loop action, the test output includes a preview_loop_values field that shows all your loop values combined together. This field is for preview purposes only—it helps you verify your loop is set up correctly by displaying all the values that will run in each loop iteration.Do not map preview_loop_values to fields in subsequent steps. This field is not available when your Zap runs live, which means your Zap will fail or produce unexpected results.Common symptoms if you accidentally use preview_loop_values:All data appears in a single row instead of creating multiple rowsYour Zap creates duplicate or concatenated dataFields appear empty when the Zap runs liveWhat to use instead: Map the individual field names you defined in your loop configuration. For example, if you named your loop value "emails", use the emails field from your loop step—not preview_loop_values.