JPEG | Blog | Iminify

Bar chart of the resized files WordPress 7.1.2 made on the server and in Chrome: 691 and 640 KB for a 1800 px photo, 1,942 and 2,193 KB for its 6000 px version, 553 and 651 KB for a PNG screenshot.

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Does WordPress compress images? What WordPress 7.1 does to your upload

We uploaded the same photo to a fresh WordPress 7.1.2 site twice, both times from Chrome. The file we sent, 832 KB, was stored byte for byte both times. From it WordPress made five resized copies at JPEG quality 82. Through Media > Add Media File those copies came to 691 KB. Through the Upload button on an Image block they came to 640 KB, because in 7.1 that button has the browser make the copies instead of the server. So does WordPress compress images automatically? Not the file you upload, which is stored byte for byte. It re-encodes the resized copies it makes, the JPEG ones at quality 82. In our test a phone and a standard laptop screen downloaded copies of this photo, but a 2x laptop screen got the untouched original, so compressing it is still your job. Since 7.1, which program makes the copies depends on the button you press and the browser you press it in.

Oct 5, 2026 8 min read

Line chart of the fjord photo's SSIMULACRA 2 score over 100 saves: ImageMagick levels off at 91.99 and Pillow at 69.77, while Pillow with 1 pixel cropped before each save and jpegli after mozjpeg's decoder both fall below -60.

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Does a JPEG lose quality every time you save it? We saved five photos 100 times

Two of the tests that come up for this question disagree. Fstoppers opened a photo in Photoshop 2020 and saved it 99 times at maximum quality, and saw "significant quality loss after you save it six times". Improve Photography saved one 30 times at maximum quality, painting a pixel white each time, and found "no noticeable reduction in image quality. None." Both judged by eye. We opened a JPEG 100 times, copied it and zipped it, then saved five photos 100 times in a row in five programs and scored every save against the file we started from. The short answer: Opening, copying and zipping never changed a byte. In every same-setting run, no later save cost as much as the first. Saving again at the same setting, with no edits, then mostly stopped costing: at their defaults, by save 73, ImageMagick, Chrome and Pillow were writing identical files on all five photos, and mozjpeg on four. Cropping one pixel or turning the photo before each save kept eating it. One pairing of two JPEG libraries lost quality with every save: the jpegli encoder fed by mozjpeg's decoder. Iminify runs that pairing, so we tested our own tool too.

Oct 1, 2026 7 min read

Bar chart of one photograph in bytes: 852,461 as served, against Lighthouse's target of 45,084 at its phone slot and encodes of 47,876 (JPEG), 46,320 (WebP) and 41,735 (AVIF).

Improve image delivery in Lighthouse: what it replaced and how it counts savings

PageSpeed Insights ran Lighthouse 13.5.0 on our home page on 22 September 2026 and flagged "Improve image delivery" in the mobile report: "Est savings of 1,300 KiB". All of it came from one photograph. The fjord shot in our before-and-after comparison is on the page twice, as the 832.5 KiB original and as our own compressed copy at 555.3 KiB. Both files are 1800x1200, and the report says they're displayed at 637x425. Three later runs that day said 1,359 KiB and 364x243. If your old notes say "Serve images in next-gen formats" or "Properly size images", this is where they went: Lighthouse 13 folded four image audits into this one insight. And its savings aren't measured: each figure is arithmetic on bytes and pixels. We reproduced every number in that insight, made the file it asks for, and traced one reason the same page gets two answers.

Sep 30, 2026 8 min read

Bar chart for one 4080x3072 phone photo, measured with each vendor's token counter: 1,102 tokens on Gemini 3.8 Flash, 4,743 on Claude Opus 5.5 and 14,746 on GPT-5.6 at default detail.

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How many tokens is an image? Claude, GPT and Gemini, measured on seven real files

A 12.5-megapixel phone photo counts 4,743 input tokens on Claude Opus 5.5, 1,102 on Gemini 3.8 Flash and 14,746 on GPT-5.6 at its default detail setting, over 13 times Gemini's count. We measured all three with the vendors' own token counters on 23 September 2026. And none of the three depends on how many bytes the file has. Claude counts pixels up to a cap, GPT-5.6 counts every pixel unless you ask for less, and Gemini 3 barely looks at the size.

Sep 29, 2026 7 min read

The fjord photograph from our test set above two bars: 3.07 MB as a PNG and 555 KB as a JPEG at quality 90.

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Why is my PNG file so large? Four causes, measured

We took the fjord photograph from our test images, a 1,800 by 1,200 JPEG of 832 KB, and saved the same pixels as a PNG. It came to 3.34 MB at the default setting of Pillow, the Python imaging library. Through zopflipng, a slower lossless compressor, 3.07 MB. As a JPEG at quality 90 it's 555 KB, and it scores 84.22 on a perceptual scale where 80 means an average observer can't see the difference side by side. A photograph was the most expensive of the four causes in the comparisons below. The four: It's a photograph. It has more pixels than it will be shown at. It stores more per pixel than the picture needs: 16 bits per colour channel, or millions of colours where 256 would do. The program that saved it didn't compress it very hard. Each has its own fix, and the fix for one can be wrong for another. A JPEG rescues a photograph. Our desktop screenshot came out bigger as a JPEG than as a PNG through zopflipng.

Sep 28, 2026 7 min read

Bar chart: a 12.5 MP phone photo at JPEG quality 90 is 4,309,090 bytes as a file and 5,745,456 bytes as base64, past a dashed line at the 5,242,880-byte limit on Bedrock and Google Cloud.

Image exceeds 5 MB maximum? Claude counts the base64, not your file

Our 12.5-megapixel test photo, re-saved with jpegli at quality 90, is 4,309,090 bytes. That's under 5 MB, and it's still too big for Claude on Amazon Bedrock or Google Cloud. Anthropic's limit there is "5 MB (base64-encoded)", and base64 turns those 4,309,090 bytes into 5,745,456. The error compares the encoded size with 5,242,880 bytes, as in this one from a Claude Code issue: image exceeds 5 MB maximum: 5281812 bytes > 5242880 bytes. So the ceiling is 3,932,160 bytes of actual file on Bedrock and Google Cloud, and roughly 7.5 MB on the direct Claude API, whose limit is 10 MB. Separately, no side may pass 8000 pixels, or 2000 once a request carries more than 20 images. For photos, one step clears all of it: resize to 2000 pixels on the long edge and save it as JPEG.

Sep 27, 2026 8 min read

The harbour picture Nano Banana 2 generated at 4K, 5504x3072: 10.51 MB as sent, a quality-100 JPEG, and 1.58 MB re-encoded as a quality-82 JPEG holding 40 dB.

How big is a Nano Banana image? 52 files measured, from 512 px to 4K

We asked Nano Banana 2 for a 4K, 16:9 picture of a fishing harbour through the Gemini API on 23 September 2026. It came back as a 5504x3072 JPEG of 10.51 MB. The same request again gave 11.10 MB. Both files were saved at JPEG quality 100, the top of the scale. So, how big is a Nano Banana image? From Nano Banana 2 or Pro, a detailed picture is roughly 1 MB at 1K, 4 MB at 2K and 10.45 to 12.13 MB at 4K, and a flat illustration less. The original Nano Banana sends a PNG instead, about 2.1 MB for the same prompt at 1024x1024. Here are the 52 images of our test set, from all four Nano Banana models, and what five of them shrink to.

Sep 26, 2026 9 min read

Twelve sites and the image format Chrome got from each on 23 September 2026: WebP from Reddit, a Shopify store, Squarespace, BBC News, eBay; AVIF from Wix, YouTube, The Guardian, Unsplash; JPEG from Pinterest, Medium, Wikipedia.

Why do images save as WebP? What 12 sites sent Chrome, and how to get the JPG

The hero photo on the Allbirds home page has a file name that ends in .jpg. On 23 September 2026 the site sent Chrome a WebP of 572 KB. Ask the same image address for a JPEG and it sends one, 663 KB. That's why your saved image is a WebP. Many sites pick the format each time they send a picture, from a list of formats your browser says it can show. Twelve sites made it into our test: nine sent Chrome a WebP or an AVIF, and every one of those nine would also hand over a JPEG (JPG is the same format) if asked the right way. The four ways that worked are below the table.

Sep 24, 2026 8 min read

Four tiles reading mozjpeg q80, jpegli q84, cwebp q90 and avifenc q74: the quality each encoder needs to match mozjpeg at 80 on every one of six photographs.

JPEG 80 is not WebP 80: what quality means in four encoders

We set four encoders to quality 80 and pointed them at one photograph, an 1800x1200 shot of a fjord. jpegli scored 74.2 on the SSIMULACRA 2 scale, mozjpeg 74.8, cwebp 72.8, avifenc 85.5. One picture, one number typed into four tools, and nearly thirteen points between the best result and the worst. Quality 80 names four unrelated parameters that happen to share a range. We measured what each produces across ten public images, worked backwards to the number every encoder needs to land in the same place, and read all four sources to see why they disagree.

Sep 21, 2026 9 min read

Bar chart: one 832 KB photo through jpegli costs 159 KB at a SSIMULACRA 2 score of 50, 311 KB at 70, 473 KB at 80 and 847 KB at 90.

SSIMULACRA 2 scores in practice: what 50, 70 and 90 cost in kilobytes

We ran cwebp at quality 75 over ten images, at the settings below. A night skyline came out at 63.0 on the SSIMULACRA 2 scale, an app icon at 83.1. Same encoder, same quality number, twenty points apart, and 63 sits below the line the scale calls "artifacts are perceptible, but not annoying". A quality number tells the encoder how hard to try. SSIMULACRA 2 describes what came out, on a scale topping out at 100, and means much the same for a JPEG, a WebP or an AVIF. So we measured what each point costs: ten public images, three encoders, a grid of quality settings across each encoder's range, bisected around each target.

Sep 20, 2026 8 min read

Line chart on Iminify's blue gradient: from 300 to 1536 pixels wide, on a log kilobyte scale, the fjord photograph rises from 11 KB to 237 KB and the coffee shot from 2 KB to 11 KB, both at SSIMULACRA 2 score 70 through cwebp.

How many KB should a website image be? Measured at four widths

The pages that rank for "image size for website in kb" don't agree. We opened four and read what each recommends for one full-width hero image. ShortPixel says 200 KB or less. ForegroundWeb says every image on the site should be "less than 500 KB". HubSpot says "The file size is recommended at 10 MB" and adds that smaller is better, and Shopify's blog labels a hero the same, with 20 MB for a background. Fifty times between tightest and loosest, for the same picture in the same slot. Three of them pair the figure with a pixel size, which is the right instinct, and one suggests a JPEG quality to save at. None says what visual quality its number actually buys. So we measured it: ten images, four widths, three encoders, every file held to the same visual quality score. The tool that will judge the page has had a budget all along, and none of those four pages mentions that budget.

Sep 19, 2026 8 min read

Two cards next to the command avifenc -s 6 -q 60 -y 444: libavif 1.2.1 writes 38.5 KB at SSIMULACRA 2 68.2, libavif 1.4.2 writes 76.6 KB at 76.2.

What AVIF quality setting should you use? The answer changed in March 2026

We ran one avifenc command on one photo, the raspberries from our corpus, in two containers. On Debian 13, whose libavif-bin is 1.2.1, it wrote 38.5 KB. On Alpine edge, which packages libavif 1.4.2, it wrote 76.6 KB: twice the file, the biggest increase of our ten, at a SSIMULACRA 2 score of 76.2 instead of 68.2. Neither container is broken. In March 2026 libavif changed what the number means.

Sep 18, 2026 7 min read

Try it on your own images