Converting JPG to PDF: What Changes to Your Photos
ClearConvert makes a PDF from photos in your browser. We tested quality, file size, EXIF, transparency, CMYK and big files. Here is what changes.
Short answer: ClearConvert redraws every JPG and WebP in your browser and saves it into the PDF as a JPEG at quality 95, so the picture in the PDF is never a byte-for-byte copy of your file. PNG pixels go in unchanged. Transparent areas turn white, rotated photos come out upright, and the camera make, model and GPS location do not reach the PDF. Photos above about 16.8 megapixels are scaled down first.
We measured all of this on test images. They are synthetic pictures, not real photos: smooth colour gradients, fine texture and noise, sharp lines, a block of text and six saturated colour patches. Sizes on your own photos will differ, so read the ratios below as a guide to the pattern, not as a promise.
What Happens to Each Image
Every image goes through the same steps. The browser decodes it and turns it upright using its EXIF orientation tag, ClearConvert draws it on a white background, and the result is written into the PDF. The last step depends on the type. A PNG is saved as a PNG. A JPG or a WebP is saved as a new JPEG at quality 95 with 4:2:0 colour, which keeps the colour at half the width and half the height of the brightness detail. Each image gets its own page, in the order of your list.
To compare the results we used PSNR (peak signal-to-noise ratio), a standard score in decibels for how close one image is to another. Higher means closer, and two identical images have no finite score. Every PDF image was compared with the decoded source file. Differences of a point or two are not meaningful, because the decoders used for the comparison can differ by one or two levels.
| Source file | Stored in the PDF as | PDF size compared with the file | Closeness to the source |
|---|---|---|---|
| JPG, quality 60 | JPEG, quality 95 | 1.50 times | 48.4 dB |
| JPG, quality 80 | JPEG, quality 95 | 1.37 times | 47.9 dB |
| JPG, quality 90 | JPEG, quality 95 | 1.17 times | 46.6 dB |
| JPG, quality 100 | JPEG, quality 95 | 0.46 times | 38.9 dB |
| JPG, quality 90, full-resolution colour (4:4:4) | JPEG, quality 95, 4:2:0 | 0.69 times | 30.6 dB |
| PNG, no transparency | PNG, same pixels | 1.30 times | Identical, 0 differing pixels |
| PNG with transparency | Flattened onto white | 0.94 times | Exact blend onto white |
| WebP, lossy quality 80 | JPEG, quality 95 | 2.35 times | 40.4 dB |
| WebP, lossless | JPEG, quality 95 | 0.25 times | 30.1 dB |
| JPG, grayscale | JPEG, grey RGB | 1.18 times | 45.5 dB |
The JPG and PNG tests used 4000 × 3000 pixels (the PNG ratio was 1.31 at 3000 × 2000), the WebP tests 2000 × 1500, the grayscale JPG 1600 × 1200 and the transparency test 1200 × 800.
Why a JPG Is Not Copied As It Is
The table shows what redrawing costs. A low-quality JPG gets bigger, 1.50 times at quality 60, because the new file is saved at a higher quality setting than the source used. A very high-quality JPG gets smaller, 0.46 times at quality 100, because quality 95 stores less than quality 100 does, and its closeness score drops to 38.9 dB. A source with full-resolution colour (4:4:4) comes out as 4:2:0 and scores 30.6 dB, the biggest drop among the JPGs we tried.
For sources at quality 60 to 90 the scores stay between 46.6 and 48.4 dB, the smallest changes in the test. If you need the exact original JPEG bytes inside a PDF, ClearConvert is not the right tool, because it always saves the image again. If you only need your photos in one PDF to send or print, our numbers say that files at these qualities change little.
PNG and Transparency
A PNG goes in without loss. We compared the pixels in the PDF with the PNG at 3000 × 2000 and at 4000 × 3000 and found no differing pixel in either. The price is size: the PDF came out about 1.3 times larger than the PNG.
A PDF made this way has no transparency. Fully transparent areas become pure white (255, 255, 255), and half-transparent pixels are blended onto white. In our 1200 × 800 test image all 960,000 pixels matched that blend exactly.
WebP
A WebP is also saved as a JPEG. A lossy WebP at quality 80 grew to 2.35 times its size. A lossless WebP shrank to 0.25 times, but it stopped being lossless: it scored 30.1 dB against the decoded WebP on our noisy test image. If a lossless result matters, convert from a PNG instead.
Rotation, Mirroring and Metadata
Photos with EXIF orientation 6, 8 and the mirrored orientation 2 all came out upright on an A4 landscape page, with the red corner of our test image at the top left and the blue corner at the bottom right.
The camera information did not travel with them. We gave the test files a make, a model and a GPS position, then searched the raw PDF and every compressed stream in it. We found no make, no model, no GPS and no EXIF block. The PDF has no colour profile object, but each JPEG inside it carries a small generic sRGB profile (456 bytes) written by the browser, not your camera’s profile. The PDF’s own fields say ClearConvert as producer and creator and hold the date of the conversion. Title, author, subject and keywords are empty.
Colour Profiles and CMYK
A CMYK JPG with an embedded profile is converted to RGB using that profile. In our test the result differed from a profile-based conversion by 3.8 levels on average (on a scale of 0 to 255), and a pure red patch came out as a duller (227, 53, 46). A CMYK file without a profile is converted with a simple formula, and the same red stayed (254, 0, 0). A grayscale JPG becomes a grey RGB image with equal red, green and blue values.
We could not test Display P3 or Adobe RGB photos, because no such profiles were available on our test machine, so we make no claim about them. We also ran every test in one Chromium build, and other browsers may handle colour differently.
Large Photos
ClearConvert limits an image to 16,777,216 pixels (about 16.8 megapixels). A larger photo is scaled down to that size first, with its shape kept.
| Source photo | Image in the PDF | Time on our test machine |
|---|---|---|
| 12 MP, 4000 × 3000 | 4000 × 3000, unchanged | 0.53 to 0.56 seconds |
| 20 MP, 5000 × 4000 | 4579 × 3663 | 1.1 to 1.2 seconds |
| 48 MP, 8000 × 6000 | 4729 × 3547 | 1.9 to 2.2 seconds |
The page size changes only the printed size, never the pixels. A 4000 × 3000 photo on A4 with the default 10 mm margin prints at 401 pixels per inch, on Letter at 392, and with Fit to image at 150 pixels per inch on a page of about 27 × 21 inches. All three PDFs held the same 4000 × 3000 image.
Many Images at Once
Twenty JPGs of 4000 × 3000 pixels (65.1 MB in total) became a 76.2 MB PDF in about 6.8 seconds, and the page stayed responsive. A PDF of 100 JPGs of 1600 × 1200 pixels came to 35.4 MB and took about 7 seconds. Twenty PNGs of 2000 × 1500 pixels (109.5 MB) became a 142.3 MB PDF in 19 to 20 seconds, and the page stopped responding once for 10 to 11 seconds during each run. If you have a lot of PNGs, expect a wait.
What It Does Not Do
- No text recognition. The PDF holds pictures, so the text in a scanned page cannot be selected or searched.
- Only JPG, PNG and WebP. GIF, BMP, TIFF and SVG files are refused with a message, and HEIC with a hint to export the photo as JPG first.
- No transparency in the result. Transparent areas always become white.
What We Did Not Test
- Real photographs. Our images were generated.
- Display P3 and Adobe RGB colour profiles, 16-bit PNGs, and PNGs that carry their own colour profile.
- Browsers other than one Chromium build, and phones.
Try It
To make a PDF from your own photos, open JPG to PDF in ClearConvert. The files stay in your browser and are never uploaded. To go the other way and save PDF pages as images, use PDF to JPG. For the rest of the tool, see what ClearConvert is, and for text files see what survives a TXT to PDF conversion.
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For questions or inquiries contact us at info@cleartexteditor.com