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I'm making many card images using the same base, with each alteration in a separate group of layers. My PSD file just have the layers "Base", "Image 1 text", "Image 1 image", "Image 2 text", "Image 2 image", and so on. When I export an image as PNG, I make the base layer and the relevant image layers visible, then choose File > Save As..., then select type PNG. So when I need image 1 I will make only "Base", "Image 1 text" and "Image 1 image" layer visible, then save as PNG; with image 2, only "Base", "Image 2 text" and "Image 2 image", and so on.

As I add more layers to the PSD file, I notice that the result files getting bigger and bigger in file size, starting from ~1.5MB and now they are ~1.7MB each, even though the number of visible layers used for each result PNG file remain the same. What could be the cause of this?

Update: Here's the actual PSD file I'm working on and the 2 test PNG files: https://drive.google.com/drive/u/1/folders/1Sgg0JRG7Ye7xuk8ENfMffXd7_HZhY7Ia

It's a bit more than in my description, but the gist is that if I make only the "Background" layer and all layers which have name starting with A9 visible then save as PNG, the file size will be 1.7MB. If I keep the same visible layers but delete all other non-visible layers like ones starting with A2, A3, etc. then save as PNG again, the file size will be 1.5MB without any visible change compares to the first result PNG. You can compare the A9.PNG and A9_2.PNG to see the different sizes.

The A2, A3, A4 etc. are all limited-length text, that's why my result PNGs all have similar size at first. It was only after rechecking the output folder with about 20 images that I realized the file sizes have been steadily climbing.

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  • I do not quite understand. Are you adding more layers to the file, but yet the number of layers is the same? What is in those layers? Commented Sep 13, 2024 at 16:26
  • @Rafael I add more layers to the PSD but they are not toggled to visible when saving to PNG, so my understanding is that if the layers aren't visible they won't affect the final file, but they are. A file with 3 visible layers is 1.5MB, but the same file with an addition of 200+ non-visible layers is now 1.7MB. Commented Sep 13, 2024 at 16:58
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    All the answers given so far are (more or less) speculative, because that's all they can be with the information you've provided. To determine the real cause of the phenomenon you've observed, you may need to show us some of these PNG files. Preferably two that look the same but have different sizes. Someone could then analyze the contents of the files and see what's making one of them bigger than the other. Commented Sep 14, 2024 at 8:27
  • @IlmariKaronen Any two PNGs with the same dimensions, but containing different images will most likely have different file sizes. This is a fact, not speculation. If they were the same, it would be mere coincidence. The OPs expectation seems to be that two PNGs with the same dimensions should have the same file size, which is simply not true. The difference in file size is caused by the lossless compression used in the PNG format itself. Nothing really to do with Photoshop or layers. This is really just a red herring. Correlation is not causation. The same thing happens in GIMP. Commented Sep 14, 2024 at 11:21
  • I didn't know this isn't a commonly known issue, sorry everyone. I have included my working file in the question, if you could please check to see if there's anything wrong with it that will be great. Commented Sep 14, 2024 at 16:29

3 Answers 3

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PNGs don't support layers, so the number of layers you have in your original PSD file has no effect on the file size of the finished PNG file.

Here's what is really going on: PNG file sizes depend on what is in the PNG image. If the images are different in any way, it's highly unlikely they will ever be the same file size.

For example, here I have two PNG files. Both are the exact same size in pixels and resolution. The first is a photographic image which contains lots of detail. The second only contains a single plain colour fill.

enter image description here

As you can see, there is a huge difference in file size. Nothing is wrong here. It's completely normal.

This happens because raster image formats such as PNG use compression to reduce the file size. However, this compression is not as effective when there is more detail, and so the file size will be larger. Basically more detail = more data = larger file sizes.

Consequently, this means that PNG images which contain simple graphics with flat areas of colour will compress much more than something like a photographic image. This makes PNGs efficient for simple graphics, but not so efficient for detailed photographic images.

JPEG can compress photographic images much more than a PNG. So if you want a smaller file size for the web, use JPEG for photos.

This drastic difference in file size between JPEG and PNG is because they both use different kinds of compression. PNGs use lossless compression (no detail is lost during compression), but JPEGs use lossy compression where some data/detail is lost when saving. Most of the time, this loss in fidelity is not noticeable to the human eye, unless you increase the compression level too much.

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    PNGs don't support layers - True, but not for Adobe products. They support 2 types of PNGs - the usual standard PNG and a proprietary PNG format which does support layers. In fact, Adobe Fireworks actually used a proprietary PNG as its native file format which also stored metadata for layers, animation, etc... in it. As Rafael's answer points out, you need to use "Export..." to be sure that you are saving the image as a "standard" PNG (which, as you noted, doesn't support layers - "Export..." will flatten any layers in the image before exporting it as PNG). Commented Sep 13, 2024 at 20:03
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    @sfxedit You can't "save as" PNG in Photoshop if it has multiple layers. The PNG file type simply isn't available in the "Save As" dialog. You would have to flatten the layers first if you want to use that dialog to save a PNG. Only then does the file type appear. Yes, you need to use Export if you don't want to flatten, and yes, Export only creates standard PNGs with no layers. If you notice in my answer I made no reference to exporting vs saving as, because it's simply not the source of the OPs issue, and so I disagree with that part of Rafael's answer. Commented Sep 13, 2024 at 21:13
  • I checked quickly, and the Save As > PNG option doesn't appear for PSD files, like you said. But if you open a JPEG file and create multiple layers, the Save As option does show PNG. But saving the file as PNG seems to flatten the image too. Not sure if the old versions of Photoshop do the same though as, Adobe (or was it Macromedia?) did build a proprietary PNG version too. That's why I thought Rafael's answer had merit too. Commented Sep 13, 2024 at 22:03
  • @sfxedit I don't have any old versions of PS to check, and Fireworks is long gone. Fireworks was a Macromedia product originally, which Adobe later bought over, and eventually killed off. The native file format of Macromedia Fireworks was certainly a proprietary version of PNG which did include layers and vectors if I remember correctly. Macromedia developed the format, not Adobe. I don't think the products ever supported each other's formats well. I'm not aware of Photoshop ever supporting Fireworks PNGs, although I could be wrong, I just don't remember it. Commented Sep 13, 2024 at 22:43
  • @sfxedit I was a Macromedia user: Flash, Fireworks, Freehand, and Dreamweaver, back in the late 1990s, early 2000s. Also I used QuarkXpress long before InDesign existed. Adobe had Page Maker which they bought from Aldus. Macromedia's graphics suite was very popular in Europe (I'm in the UK). The only Macromedia products that technically still exist are Dreamweaver and Animate (previously called Flash). I never forgave Adobe for killing off Freehand (also previously an Aldus product acquired from Altsys originally) which was IMHO far superior to Illustrator back then Commented Sep 13, 2024 at 23:28
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Now that you've shared some example files we can take a closer look at what's in them.

Specifically, let's take a look at the two PNG files in your Google Drive folder:

  • A9.png: 720 × 1098 px, 8-bit/color RGBA, non-interlaced, 1 590 593 bytes
  • A9_2.png: 720 × 1098 px, 8-bit/color RGBA, non-interlaced, 1 731 638 bytes

The first observation is that the difference in file size isn't that large: the bigger file is less than 10% larger than the smaller one.

Also, while both files have the same pixel dimensions, color format and interlacing settings, visual inspection shows that they don't contain exactly the same image: the second one has slightly more text in the lowest text box. That alone could explain the size difference, since images with more complex details (such as letters) tend to compress worse.

However, before we jump into conclusions, let's take a look at the images in an online PNG file inspector. This is a single-page JavaScript web app that decodes the PNG file data and displays information about what types of data the file actually contains and how it's encoded.

Comparing the analysis of the two images, we do see a clear difference:

  • A9.png contains nothing but the 8 byte PNG file signature, a standard 13 byte header (IHDR) chunk, a bunch of image data and a final end-of-file (IEND) chunk. In particular, this file contains no metadata chunks at all (unless you count the mandatory IHDR chunk).

    For some reason the image data in this file is divided into 194 consecutive image data (IDAT) chunks of 8192 bytes each (except for the last on, which is only 7164 bytes long), but that only wastes 12 × 193 bytes in extra chunk headers.

  • Meanwhile, A9_2.png also starts with the same 8 byte signature and 13 byte header (IHDR) chunk, but also contains a bunch of additional metadata chunks.

    In particular, the header is first followed by a 9 byte physical pixel dimensions (pHYs) chunk indicating that the physical resolution of the image is supposed to be 11811 pixels per meter, or approximately 300 DPI. Then follows a 712 byte compressed Photoshop ICC color profile (iCCP) chunk, and after that a 131 164 byte uncompressed(!) "international textual data" (iTXt) chunk containing XMP metadata.

    The contents of this XMP metadata chunk looks like this (with line breaks and indentation added for readability, and some repetitive data skipped):

    <?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?> <x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="Adobe XMP Core 5.6-c138 79.159824, 2016/09/14-01:09:01 "> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"> <rdf:Description rdf:about="" xmlns:xmp="http://ns.adobe.com/xap/1.0/" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:photoshop="http://ns.adobe.com/photoshop/1.0/" xmlns:xmpMM="http://ns.adobe.com/xap/1.0/mm/" xmlns:stEvt="http://ns.adobe.com/xap/1.0/sType/ResourceEvent#" xmlns:stRef="http://ns.adobe.com/xap/1.0/sType/ResourceRef#" xmlns:tiff="http://ns.adobe.com/tiff/1.0/" xmlns:exif="http://ns.adobe.com/exif/1.0/"> <xmp:CreatorTool>Adobe Photoshop CC 2017 (Windows)</xmp:CreatorTool> <xmp:CreateDate>2016-12-04T22:02:51-05:00</xmp:CreateDate> <xmp:ModifyDate>2024-09-15T00:21:19+07:00</xmp:ModifyDate> <xmp:MetadataDate>2024-09-15T00:21:19+07:00</xmp:MetadataDate> <dc:format>image/png</dc:format> <photoshop:ColorMode>3</photoshop:ColorMode> <photoshop:ICCProfile>Scanner RGB Profile</photoshop:ICCProfile> <photoshop:TextLayers> <rdf:Bag> <rdf:li rdf:parseType="Resource"> <photoshop:LayerName>Yuggoth Name</photoshop:LayerName> <photoshop:LayerText>Yuggoth</photoshop:LayerText> </rdf:li> <rdf:li rdf:parseType="Resource"> <photoshop:LayerName>Unknown Kadath Name</photoshop:LayerName> <photoshop:LayerText>Unknown Kadath</photoshop:LayerText> </rdf:li> <rdf:li rdf:parseType="Resource"> <photoshop:LayerName>The Past Name</photoshop:LayerName> <photoshop:LayerText>The Past</photoshop:LayerText> </rdf:li> --- 1735 LINES SKIPPED --- <rdf:li rdf:parseType="Resource"> <photoshop:LayerName>A1 Pass effect copy</photoshop:LayerName> <photoshop:LayerText>You try to remember if this celestial phenomenon has any deeper significance (). If you pass, you can use the stars to your advantage; close this Gate. If you fail, a cosmic disturbance occurs; move this Gate to a random space. </photoshop:LayerText> </rdf:li> <rdf:li rdf:parseType="Resource"> <photoshop:LayerName>A1 Initial effect 4 copy</photoshop:LayerName> <photoshop:LayerText>constellations, a black shooting star sails across sky, a dark speck in front of the unusual colors (–1). </photoshop:LayerText> </rdf:li> <rdf:li rdf:parseType="Resource"> <photoshop:LayerName>A1 Initial effect 3 copy</photoshop:LayerName> <photoshop:LayerText>stars. As you look into the alien</photoshop:LayerText> </rdf:li> <rdf:li rdf:parseType="Resource"> <photoshop:LayerName>A1 Initial effect 2 copy</photoshop:LayerName> <photoshop:LayerText>odd colors of dimly lit clouds of</photoshop:LayerText> </rdf:li> <rdf:li rdf:parseType="Resource"> <photoshop:LayerName>A1 Initial effect 1 copy</photoshop:LayerName> <photoshop:LayerText>The strange night sky is full of</photoshop:LayerText> </rdf:li> </rdf:Bag> </photoshop:TextLayers> <photoshop:DocumentAncestors> <rdf:Bag> <rdf:li>0F2CDBBC7B2C277AE89ECD699B433C65</rdf:li> <rdf:li>19A43FB1F6CB8DEE34D915F48273F34F</rdf:li> <rdf:li>26F2B6FB725F2EE9978DC621B509C06B</rdf:li> <rdf:li>38B5CC828B505F091706EF60184A96C7</rdf:li> <rdf:li>39903A89AF72B9AD0B0D2A0E2FF7F695</rdf:li> <rdf:li>4B439263FBC751408CAD1A1B19F08B98</rdf:li> <rdf:li>5CB9A78F2536D6B5887E2AD44A26733F</rdf:li> <rdf:li>75BD3BDAFCB72464F3148AD8F59BA78D</rdf:li> <rdf:li>9DB29253E91E74E13B68CDBD1FCB39FB</rdf:li> <rdf:li>9EDC2A7A881B8409D9E76A7748964E18</rdf:li> <rdf:li>F41D35E30DE3E4F16E98566B48046120</rdf:li> <rdf:li>adobe:docid:photoshop:35c877ed-15da-11ec-a694-e5b895fb3fad</rdf:li> <rdf:li>adobe:docid:photoshop:41c7e45b-e9dc-11eb-87db-dfcf88ba46b0</rdf:li> <rdf:li>adobe:docid:photoshop:533668f5-ecfe-11eb-b98f-ab5c08391609</rdf:li> <rdf:li>adobe:docid:photoshop:5349a62c-89a8-9c49-81c4-edd0580947e6</rdf:li> <rdf:li>adobe:docid:photoshop:651c1e22-fd1f-11ee-9d15-c80952b7f06c</rdf:li> <rdf:li>adobe:docid:photoshop:716dd102-ea95-11eb-87dc-98eba39871b3</rdf:li> <rdf:li>adobe:docid:photoshop:71ab6b77-6772-1179-8d6d-f3d7ffa83e2c</rdf:li> <rdf:li>adobe:docid:photoshop:76b5415a-e9b4-11eb-a15e-c72f401d2fa6</rdf:li> <rdf:li>adobe:docid:photoshop:89c7f89b-87b1-11ec-a7b3-93cb402cf21e</rdf:li> <rdf:li>adobe:docid:photoshop:a3ff76b3-f7fe-11eb-a1cd-f3dada33105f</rdf:li> <rdf:li>adobe:docid:photoshop:d47e1b74-e51b-11eb-876e-d77239026d83</rdf:li> <rdf:li>adobe:docid:photoshop:d5856ad6-e9db-11eb-87db-dfcf88ba46b0</rdf:li> <rdf:li>adobe:docid:photoshop:ee4e9e31-ea97-11eb-87dc-98eba39871b3</rdf:li> <rdf:li>uuid:1D3842ADEFBFE911855786553090093A</rdf:li> <rdf:li>uuid:47B2078DEDBFE911855786553090093A</rdf:li> <rdf:li>uuid:55A9CBF703BFE911B789FFF8570156C6</rdf:li> <rdf:li>uuid:91B7FE36CD1BE31184C086B06A19545E</rdf:li> <rdf:li>uuid:c187a7bb-c7ca-4bc9-aec4-f61f5734e1ab</rdf:li> <rdf:li>xmp.did:04ED0FA1D625E7119899A1B2643677E0</rdf:li> <rdf:li>xmp.did:05F03CD3537711E7B1B1EB2A3A5DFB11</rdf:li> <rdf:li>xmp.did:31168F76D4DBE011931FD2E5B450B6D3</rdf:li> <rdf:li>xmp.did:426abcd3-f41e-da48-837e-b71decc8d1df</rdf:li> <rdf:li>xmp.did:49473B09F54011E6BD699EA6CCC700CC</rdf:li> <rdf:li>xmp.did:4C3291A581CEE511BF7E90DD08DD61B1</rdf:li> <rdf:li>xmp.did:5097DEA8E11EE711A8E0C345738BAA96</rdf:li> <rdf:li>xmp.did:63BB60CF2E1AE711AB168C6940F11F91</rdf:li> <rdf:li>xmp.did:6FE0CFC08BDAE211951AC2326FCA1BCC</rdf:li> <rdf:li>xmp.did:705af333-d9b0-45e6-8a1d-f8d1a36ded1e</rdf:li> <rdf:li>xmp.did:99723e22-5685-2b46-8d5b-133db03efdac</rdf:li> <rdf:li>xmp.did:BC8DBC7A4F3311E5B0B0D70322962D00</rdf:li> <rdf:li>xmp.did:D49FB9BFEFFCE611B29EDBFB42D8CFEE</rdf:li> <rdf:li>xmp.did:E694EAC92EA911E39590E7F61E99FC18</rdf:li> <rdf:li>xmp.did:E695DA887ECF11E7ABFECC046AFF3941</rdf:li> <rdf:li>xmp.did:c67d6b3d-35c4-bf47-845c-a3f6f04b3f45</rdf:li> </rdf:Bag> </photoshop:DocumentAncestors> <xmpMM:InstanceID>xmp.iid:bc7ce7d1-886b-8f41-ad3b-f07df1d1fcb8</xmpMM:InstanceID> <xmpMM:DocumentID>adobe:docid:photoshop:b4a71175-72bd-11ef-83b5-d2db3f90f45d</xmpMM:DocumentID> <xmpMM:OriginalDocumentID>xmp.did:03801174072068118F62C39C098C8D90</xmpMM:OriginalDocumentID> <xmpMM:History> <rdf:Seq> <rdf:li rdf:parseType="Resource"> <stEvt:action>created</stEvt:action> <stEvt:instanceID>xmp.iid:03801174072068118F62C39C098C8D90</stEvt:instanceID> <stEvt:when>2016-12-04T22:09:55-05:00</stEvt:when> <stEvt:softwareAgent>Adobe Photoshop Elements 8.0 Macintosh</stEvt:softwareAgent> </rdf:li> <rdf:li rdf:parseType="Resource"> <stEvt:action>converted</stEvt:action> <stEvt:parameters>from image/jpeg to application/vnd.adobe.photoshop</stEvt:parameters> </rdf:li> <rdf:li rdf:parseType="Resource"> <stEvt:action>saved</stEvt:action> <stEvt:instanceID>xmp.iid:04801174072068118F62C39C098C8D90</stEvt:instanceID> <stEvt:when>2016-12-04T22:09:55-05:00</stEvt:when> <stEvt:softwareAgent>Adobe Photoshop Elements 8.0 Macintosh</stEvt:softwareAgent> <stEvt:changed>/</stEvt:changed> </rdf:li> <rdf:li rdf:parseType="Resource"> <stEvt:action>saved</stEvt:action> <stEvt:instanceID>xmp.iid:0e97f579-96d9-f046-8301-9c4b90397068</stEvt:instanceID> <stEvt:when>2024-09-15T00:21:19+07:00</stEvt:when> <stEvt:softwareAgent>Adobe Photoshop CC 2017 (Windows)</stEvt:softwareAgent> <stEvt:changed>/</stEvt:changed> </rdf:li> <rdf:li rdf:parseType="Resource"> <stEvt:action>converted</stEvt:action> <stEvt:parameters>from application/vnd.adobe.photoshop to image/png</stEvt:parameters> </rdf:li> <rdf:li rdf:parseType="Resource"> <stEvt:action>derived</stEvt:action> <stEvt:parameters>converted from application/vnd.adobe.photoshop to image/png</stEvt:parameters> </rdf:li> <rdf:li rdf:parseType="Resource"> <stEvt:action>saved</stEvt:action> <stEvt:instanceID>xmp.iid:bc7ce7d1-886b-8f41-ad3b-f07df1d1fcb8</stEvt:instanceID> <stEvt:when>2024-09-15T00:21:19+07:00</stEvt:when> <stEvt:softwareAgent>Adobe Photoshop CC 2017 (Windows)</stEvt:softwareAgent> <stEvt:changed>/</stEvt:changed> </rdf:li> </rdf:Seq> </xmpMM:History> <xmpMM:DerivedFrom rdf:parseType="Resource"> <stRef:instanceID>xmp.iid:0e97f579-96d9-f046-8301-9c4b90397068</stRef:instanceID> <stRef:documentID>adobe:docid:photoshop:df7d0975-6232-11ef-9cbc-8af1b9285a6e</stRef:documentID> <stRef:originalDocumentID>xmp.did:03801174072068118F62C39C098C8D90</stRef:originalDocumentID> </xmpMM:DerivedFrom> <tiff:Orientation>1</tiff:Orientation> <tiff:XResolution>3000000/10000</tiff:XResolution> <tiff:YResolution>3000000/10000</tiff:YResolution> <tiff:ResolutionUnit>2</tiff:ResolutionUnit> <tiff:Make>KODAK</tiff:Make> <tiff:Model>VERITE 50 Series</tiff:Model> <exif:ColorSpace>65535</exif:ColorSpace> <exif:PixelXDimension>720</exif:PixelXDimension> <exif:PixelYDimension>1098</exif:PixelYDimension> </rdf:Description> </rdf:RDF> </x:xmpmeta> <?xpacket end="w"?>

    This is then followed by a 32 byte chromaticity data (cHRM) chunk, a single 1 599 616 byte compressed image data (IDAT) chunk and finally the end-of-file (IEND) chunk.

In other words, your two PNG image files contain nearly the same amount of actual compressed image data (1 588 220 vs. 1 599 616 bytes). However, the larger file also contains a significant amount of metadata, most notably over 130 kilobytes of XMP metadata including the names and contents of all your text layers.

Normally one wouldn't expect a little bit of textual metadata to increase the size of an image file too much, but in your case you have a lot of text layers in your PSD file and it adds up. Worse yet, since this metadata is stored uncompressed in an XML-based format, the repeated XML tag names consume even more space. (XML data like this would compress really well, since it contains a lot of repeated text, but for some reason Photoshop has chosen not to apply compression to it.)

So why does this happen and how can you avoid it?

This part of my answer is necessarily a bit speculative, since I don't use Photoshop myself and don't have a license to it. That said, the obvious explanation is that you used a different method of exporting the two PNG files from Photoshop or selected different options when exporting the files.

In particular, when exporting a PNG image from Photoshop, there should be some option (possibly hidden under "advanced settings" or something similar) to choose whether or not you want to export XMP metadata. If you don't want your PNG files bloated with all this extra data (including the text of all your PSD text layers), unselect that option.

Alternatively you can run your images through a PNG optimizer after exporting them. There are plenty of such tools of varying speed and efficiency, but pretty much all of them can at least remove unnecessary metadata. The better ones, such as PNGOUT or Oxipng, can also recompress the image data itself using a more efficient (but slower) compression routine, which can often shave a further 10% or more off the image size even after metadata removal.

For example, running oxipng -o max --fast --strip=all A9*.png reduces the file size of A9.png by 6.4% down to 1 489 378 bytes and the size of A9_2.png by 12.6% down to 1 512 793 bytes, significantly smaller than either file straight out of Photoshop.

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  • Yes there are different ways to export PNGs in PS: Save as, Export as, Quick Export, and Save for Web (Legacy). Potentially using different methods could explain the metadata and ICC profiles - but it's really not a lot of data. The files will never be exactly the same size anyway, because the images are slightly different. One way to strip all of that layer name rubbish would be to flatten before export (an extra step though), and after export, the OP would have to undo before repeating with the next set of layers. This may be more trouble than it's worth, to save a few hundred kb. Commented Sep 15, 2024 at 10:20
  • I came back to this answer by accident. If anyone wonders how I end up reducing the size, instead of File > Save As... use File > Export As... and the image will be smaller. PNGOUT as suggested by Ilmari is also a good batch option. Commented Dec 17, 2024 at 9:56
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You are not "saving as PNG", you are "exporting to PNG".

The difference is that "saving" retains the info of the file. Layers, blending modes, masks, etc.

Exporting makes a flattened output file. It could change the bit depth, color space, color mode, etc. But some "save" dialog boxes mislead you into thinking it is the same.

In some rare cases, it can export more or less working layers, but that depends on the compatibility of the target format. For example, Gimp can save as its native file format and export decently to PSD files. But that is not the case with a normal PNG.

And I mean "normal" PNG because at some time an application of Adobe used that extension as a native file for its software, and it contained layers among other elements.

A normal PNG does not care about the layers, it cares about the uniformity of the zones of pixels.

If you have one big flat zone it will compress nicely.

If you segment that zone or add texture or text, the uniformity is broken, then it will compress less.

It could be the case that by activating more layers, you are adding a bit of complexity to the final file, therefore it compresses a bit less.

The change could be imperceptible to the naked eye, probably a difference in 1 value over some pixels.

Or it could be just Photoshop doing something else processing the file when exporting.

There is not 1 internal algorithm to compress PNG files. To my understanding, there are 256. So probably Photoshop is just confused.

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  • "The difference is that "saving" retains the info of the file. Layers, blending modes, masks, etc." ermmm. you sure about that? It's not the case here. Commented Sep 14, 2024 at 2:03
  • That is why I am saying that you do not save as PNG, you export as PNG. Adobe uses words very irresponsibly. Commented Sep 14, 2024 at 4:45
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    Sorry, maybe I read it weird. I know you know your stuff. Wasn't questioning your knowledge at all, perhaps more how it was phrased. Since it is possible to BOTH save AND export as PNG - neither of which retain layers. Commented Sep 14, 2024 at 5:18

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